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Solution-processed high-performing ambipolar organic phototransistors (OPTs) can enable low-cost integrated circuits. Here, a heteroatom engineering approach to modify the electron affinity of a low band gap diketopyrrolopyrole (DPP) co-polymer, resulting in well-balanced charge transport, a more preferential edge-on orientation and higher crystallinity, is demonstrated. Changing the comonomer heteroatom from sulfur (benzothiadiazole (BT)) to oxygen (benzooxadiazole (BO)) leads to an increased electron affinity and introduces higher ambipolarity. Organic thin film transistors fabricated from the novel PDPP-BO exhibit charge carrier mobility of 0.6 and 0.3 cm2 Vs⁻1 for electrons and holes, respectively. Due to the high sensitivity of the PDPP-based material and the balanced transport in PDPP-BO, its application as an NIR detector in an OPT architecture is presented. By maintaining a high on/off ratio (9 × 104), ambipolar OPTs are shown with photoresponsivity of 69 and 99 A W⁻1 and specific detectivity of 8 × 107 for the p-type operation and 4 × 109 Jones for the n-type regime. The high symmetric NIR-ambipolar OPTs are also evaluated as ambipolar photo-inverters, and show a 46% gain enhancement under illumination. © 2024 The Authors. Advanced Materials published by Wiley-VCH GmbH.

The inefficient charge transport and large exciton binding energy of quasi-2D perovskites pose challenges to the emission efficiency and roll-off issues for perovskite light-emitting diodes (PeLEDs) despite excellent stability compared to 3D counterparts. Herein, alkyldiammonium cations with different molecular sizes, namely 1,4-butanediamine (BDA), 1,6-hexanediamine (HDA) and 1,8-octanediamine (ODA), are employed into quasi-2D perovskites, to simultaneously modulate the injection efficiency and recombination dynamics. The size increase of the bulky cation leads to increased excitonic recombination and also larger Auger recombination rate. Besides, the larger size assists the formation of randomly distributed 2D perovskite nanoplates, which results in less efficient injection and deteriorates the electroluminescent performance. Moderate exciton binding energy, suppressed 2D phases and balanced carrier injection of HDA-based PeLEDs contribute to a peak external quantum efficiency of 21.9%, among the highest in quasi-2D perovskite based near-infrared devices. Besides, the HDA-PeLED shows an ultralong operational half-lifetime T50 up to 479 h at 20 mA cm-2, and sustains the initial performance after a record-level 30 000 cycles of ON-OFF switching, attributed to the suppressed migration of iodide anions into adjacent layers and the electrochemical reaction in HDA-PeLEDs. This work provides a potential direction of cation design for efficient and stable quasi-2D-PeLEDs. The chain length tuning of alkyldiammonium cations in quasi-two dimensional perovskites is utilized to modulate the recombination dynamics and injection efficiency of perovskite light-emitting diodes. A moderate exciton binding energy, efficient energy transfer and balanced carrier injection in quasi-two dimensional perovskite based on cation with appropriate length contribute to an external quantum efficiency of 21.9% and reduced roll-off issue. image

Side chain engineering plays a vital role in exploring high-performance small molecule acceptors (SMAs) for organic solar cells (OSCs). In this work, we designed and synthesized a series of A-DA'D-A type SMAs by introducing different N-substituted alkyl and ester alkyl side chains on benzotriazole (BZ) central unit and aimed to investigate the effect of different ester substitution positions on photovoltaic performances. All the new SMAs with ester groups exhibit lower the lowest unoccupied molecular orbital (LUMO) energy levels and more blue-shifted absorption, but relatively higher absorption coefficients than alkyl chain counterpart. After blending with the donor PM6, the ester side chain-based devices demonstrate enhanced charge mobility, reduced amorphous intermixing domain size and long-lived charge transfer state compared to the alkyl chain counterpart, which are beneficial to achieve higher short-circuit current density (J(sc)) and fill factor (FF), simultaneously. Thereinto, the PM6 : BZ-E31 based device achieves a higher power conversion efficiency (PCE) of 18.33 %, which is the highest PCE among the OSCs based on the SMAs with BZ-core. Our work demonstrated the strategy of ester substituted side chain is a feasible and effective approach to develop more efficient SMAs for OSCs.

The emission peak shift caused by ion motion, especially under high bias voltage, is an obstacle to the development of blue perovskite light-emitting diodes (PeLEDs). In this work, 3-Aminopiperidine dihydrochloride (3AP) to construct heterocyclic dication Dion-Jacobson (DJ) PeLEDs is introduced, and found that 3AP incorporation can retard the halide segregation and chloride loss, leading to the improvement of the emission spectral stability. By increasing the amount of 3AP (DJ phase), emission centers can be tuned from green to blue but the excitonic peak abnormally disappears, indicative of exciton delocalization. Photoluminescence quantum yield (PLQY) and ultrafast spectroscopy indicated that the introduction of 3AP can passivate defects and control the exciton delocalization to facilitate interlayer charge transfer. The external quantum efficiencies (EQE) of the obtained green (513 nm), sky blue (488 nm), and blue (478 nm) PeLEDs reached 3.0%, 7.1%, and 4.8%, respectively, and the maximum luminance is 10956, 1093 and 782 cd m−2, respectively. Most importantly, under high operating voltages from 3 to 10 V, the PeLEDs delivered outstanding spectral stability free of peak shift.

Unfused-ring acceptors with different electron-deficient central units, dithieno[3,2-f:2′,3′-h]quinoxaline (KS40) and dithieno[3,2-e:2′,3′-g]-2,1,3-benzoxadiazole (KS41) are synthesized and characterized. When blended with PM6, KS40 with a weaker electron-accepting quinoxaline exhibits a much higher open-circuit voltage (VOC) of 0.945 V. As a result, the KS40-based device achieves a power conversion efficiency (PCE) of 12.2%. PM6:KS41-based devices, in contrast, afford improved charge mobilities as well as suppressed recombination behavior, which eventually leads to an improvement in the fill factor (72.4%). Consequently, the device is able to achieve a PCE of 11.6%. © 2024 Wiley-VCH GmbH.

Dielectric constant of non-fullerene acceptors plays a critical role in organic solar cells in terms of exciton dissociation and charge recombination. Current acceptors feature a dielectric constant of 3-4, correlating to relatively high recombination loss. We demonstrate that selenium substitution on acceptor central core can effectively modify molecule dielectric constant. The corresponding blend film presents faster hole-transfer of ~5 ps compared to the sulfur-based derivative (~10 ps). However, the blends with Se-acceptor also show faster charge recombination after 100 ps upon optical pumping, which is explained by the relatively disordered stacking of the Se-acceptor. Encouragingly, dispersing the Se-acceptor in an optimized organic solar cell system can interrupt the disordered aggregation while still retain high dielectric constant. With the improved dielectric constant and optimized fibril morphology, the ternary device exhibits an obvious reduction of non-radiative recombination to 0.221 eV and high efficiency of 19.0%. This work unveils heteroatom-substitution induced dielectric constant improvement, and the associated exciton dynamics and morphology manipulation, which finally contributes to better material/device design and improved device performance. © The Author(s) 2024.

Non-fullerene acceptors (NFAs) have enabled power conversion efficiencies exceeding 19% in organic solar cells (OSCs). However, the open-circuit voltage of OSCs remains low relative to their optical gap due to excessive non-radiative recombination, and this now limits performance. Here, an important aspect of OSC design is considered, namely management of the triplet exciton population formed after non-geminate charge recombination. By comparing the blends PM6:Y11 and PM6:Y6, it is shown that the greater crystallinity of the NFA domains in PM6:Y11 leads to a higher rate of triplet-triplet annihilation (TTA). This is attributed to the four times larger ground state dipole moment of Y11 versus Y6, which improves the long range NFA out-of-plane ordering. Since TTA converts a fraction of the non-emissive triplet states into bright singlet states, it has the potential to reduce non-radiative voltage losses. Through a kinetic analysis of the recombination processes under 1-Sun illumination, a framework is provided for determining the conditions under which TTA may improve OSC performance. If these could be satisfied, TTA has the potential to reduce non-radiative voltage losses by up to several tens of millivolts., Funding Agencies|Leverhulme Trust [ECF-2022-445]; UK Engineering and Physical Sciences Research Council (EPSRC) Application Targeted and Integrated Photovoltaics (ATIP) project [EP/T028513/1]; UK EPSRC [EP/L016702/1]; EPSRC [EP/W017091/1]; National Natural Science Foundation of China [521253, 22005347]; Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the Research Training School "Molecular biradicals: Structure, properties and reactivity" [GRK2112]; Bavarian Ministry of the Environment and Consumer Protection, the Bavarian Network "Solar Technologies Go Hybrid"; China Scholarship Council (CSC); Research Grant Council of Hong Kong [14303519]

Non-fullerene acceptors (NFAs) have enabled power conversion efficiencies exceeding 19% in organic solar cells (OSCs). However, the open-circuit voltage of OSCs remains low relative to their optical gap due to excessive non-radiative recombination, and this now limits performance. Here, an important aspect of OSC design is considered, namely management of the triplet exciton population formed after non-geminate charge recombination. By comparing the blends PM6:Y11 and PM6:Y6, it is shown that the greater crystallinity of the NFA domains in PM6:Y11 leads to a higher rate of triplet-triplet annihilation (TTA). This is attributed to the four times larger ground state dipole moment of Y11 versus Y6, which improves the long range NFA out-of-plane ordering. Since TTA converts a fraction of the non-emissive triplet states into bright singlet states, it has the potential to reduce non-radiative voltage losses. Through a kinetic analysis of the recombination processes under 1-Sun illumination, a framework is provided for determining the conditions under which TTA may improve OSC performance. If these could be satisfied, TTA has the potential to reduce non-radiative voltage losses by up to several tens of millivolts., Funding Agencies|Leverhulme Trust [ECF-2022-445]; UK Engineering and Physical Sciences Research Council (EPSRC) Application Targeted and Integrated Photovoltaics (ATIP) project [EP/T028513/1]; UK EPSRC [EP/L016702/1]; EPSRC [EP/W017091/1]; National Natural Science Foundation of China [521253, 22005347]; Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the Research Training School "Molecular biradicals: Structure, properties and reactivity" [GRK2112]; Bavarian Ministry of the Environment and Consumer Protection, the Bavarian Network "Solar Technologies Go Hybrid"; China Scholarship Council (CSC); Research Grant Council of Hong Kong [14303519]

Non-fullerene acceptors (NFAs) have enabled power conversion efficiencies exceeding 19% in organic solar cells (OSCs). However, the open-circuit voltage of OSCs remains low relative to their optical gap due to excessive non-radiative recombination, and this now limits performance. Here, an important aspect of OSC design is considered, namely management of the triplet exciton population formed after non-geminate charge recombination. By comparing the blends PM6:Y11 and PM6:Y6, it is shown that the greater crystallinity of the NFA domains in PM6:Y11 leads to a higher rate of triplet-triplet annihilation (TTA). This is attributed to the four times larger ground state dipole moment of Y11 versus Y6, which improves the long range NFA out-of-plane ordering. Since TTA converts a fraction of the non-emissive triplet states into bright singlet states, it has the potential to reduce non-radiative voltage losses. Through a kinetic analysis of the recombination processes under 1-Sun illumination, a framework is provided for determining the conditions under which TTA may improve OSC performance. If these could be satisfied, TTA has the potential to reduce non-radiative voltage losses by up to several tens of millivolts., Funding Agencies|Leverhulme Trust [ECF-2022-445]; UK Engineering and Physical Sciences Research Council (EPSRC) Application Targeted and Integrated Photovoltaics (ATIP) project [EP/T028513/1]; UK EPSRC [EP/L016702/1]; EPSRC [EP/W017091/1]; National Natural Science Foundation of China [521253, 22005347]; Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the Research Training School "Molecular biradicals: Structure, properties and reactivity" [GRK2112]; Bavarian Ministry of the Environment and Consumer Protection, the Bavarian Network "Solar Technologies Go Hybrid"; China Scholarship Council (CSC); Research Grant Council of Hong Kong [14303519]

Non-fullerene acceptors based organic solar cells represent the frontier of the field, owing to both the materials and morphology manipulation innovations. Non-radiative recombination loss suppression and performance boosting are in the center of organic solar cell research. Here, we developed a non-monotonic intermediate state manipulation strategy for state-of-the-art organic solar cells by employing 1,3,5-trichlorobenzene as crystallization regulator, which optimizes the film crystallization process, regulates the self-organization of bulk-heterojunction in a non-monotonic manner, i.e., first enhancing and then relaxing the molecular aggregation. As a result, the excessive aggregation of non-fullerene acceptors is avoided and we have achieved efficient organic solar cells with reduced non-radiative recombination loss. In PM6:BTP-eC9 organic solar cell, our strategy successfully offers a record binary organic solar cell efficiency of 19.31% (18.93% certified) with very low non-radiative recombination loss of 0.190 eV. And lower non-radiative recombination loss of 0.168 eV is further achieved in PM1:BTP-eC9 organic solar cell (19.10% efficiency), giving great promise to future organic solar cell research.

All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5–Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5–Y5. The drying process of PBDBT:PF5–Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution.

All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5–Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5–Y5. The drying process of PBDBT:PF5–Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution.

All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5-Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5-Y5. The drying process of PBDBT:PF5-Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution., Funding Agencies|Knut and Alice Wallenberg foundation [2017.0186, 2016.0059]; Swedish Government Research Area in Materials Science on Functional Materials at Linkoeping University [200900971]; China Scholarship Council (CSC) [201708370115]; Swedish Research Council; Swedish Energy Agency; National Natural Science Foundation of China [21903017]

All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5-Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5-Y5. The drying process of PBDBT:PF5-Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution., Funding Agencies|Knut and Alice Wallenberg foundation [2017.0186, 2016.0059]; Swedish Government Research Area in Materials Science on Functional Materials at Linkoeping University [200900971]; China Scholarship Council (CSC) [201708370115]; Swedish Research Council; Swedish Energy Agency; National Natural Science Foundation of China [21903017]

All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5-Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5-Y5. The drying process of PBDBT:PF5-Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution., Funding Agencies|Knut and Alice Wallenberg foundation [2017.0186, 2016.0059]; Swedish Government Research Area in Materials Science on Functional Materials at Linkoeping University [200900971]; China Scholarship Council (CSC) [201708370115]; Swedish Research Council; Swedish Energy Agency; National Natural Science Foundation of China [21903017]

Electronic devices based on tin halide perovskites often exhibit a poor operational stability. Here, we report an additive engineering strategy to realize high-performance and stable field-effect transistors (FETs) based on 3D formamidinium tin iodide (FASnI3) films. By comparatively studying the modification effects of two additives, i.e., phenethylammonium iodide and 4-fluorophenylethylammonium iodide via combined experimental and theoretical investigations, we unambiguously point out the general effects of phenethylammonium (PEA) and its fluorinated derivative (FPEA) in enhancing crystallization of FASnI3 films and the unique role of fluorination in reducing structural defects, suppressing oxidation of Sn2+ and blocking oxygen and water involved defect reactions. The optimized FPEA-modified FASnI3 FETs reach a record high field-effect mobility of 15.1 cm2/(V·s) while showing negligible hysteresis. The devices exhibit less than 10% and 3% current variation during over 2 h continuous bias stressing and 4200-cycle switching test, respectively, representing the best stability achieved so far for all Sn-based FETs.

The bulk heterojunction (BHJ) morphology of photovoltaic materials is crucial to the fundamental optoelectronic properties of organic solar cells (OSCs). However, in the photoactive layer, the intrinsic crystalline packing structure of Y6, currently the hallmark molecule among Y-series non-fullerene acceptors (NFAs), has not been unambiguously determined. Here, employing grazing-incidence wide-angle X-ray scattering (GIWAXS), we managed to uncover the intrinsic crystalline packing structure of Y6 in the BHJ active layer of OSCs, which is found to be different from its single-crystal structure reported previously. Moreover, we find that solvent additive 1-chloronaphthalene (CN) can induce highly ordered packing of Y6 in BHJ thin films. With the help of atomistic molecular dynamics simulations, it is revealed that pi-pi interactions generally exist between naphthalene derivatives and IC terminals of Y6 analogues, which would essentially improve their long-range ordering. Our work reveals the intrinsic crystalline packing structure of Y6 in the BHJ active layer as well as its crystallization mechanism in thin films, thus providing direct correlations between this crystalline packing and the device characteristics and photophysical properties., Funding Agencies|We thank the Research Grants Council (RGC) of Hong Kong (General Research Fund No. 14303519) and CUHK direct grant (no. 4442384). We also thank the beam time and technical support provided by the 19U2 beamline at SSRF, Shanghai. We appreciate Prof. Michael

Non-fullerene acceptors (NFAs) have enabled power conversion efficiencies exceeding 19% in organic solar cells (OSCs). However, the open-circuit voltage of OSCs remains low relative to their optical gap due to excessive non-radiative recombination, and this now limits performance. Here, an important aspect of OSC design is considered, namely management of the triplet exciton population formed after non-geminate charge recombination. By comparing the blends PM6:Y11 and PM6:Y6, it is shown that the greater crystallinity of the NFA domains in PM6:Y11 leads to a higher rate of triplet-triplet annihilation (TTA). This is attributed to the four times larger ground state dipole moment of Y11 versus Y6, which improves the long range NFA out-of-plane ordering. Since TTA converts a fraction of the non-emissive triplet states into bright singlet states, it has the potential to reduce non-radiative voltage losses. Through a kinetic analysis of the recombination processes under 1-Sun illumination, a framework is provided for determining the conditions under which TTA may improve OSC performance. If these could be satisfied, TTA has the potential to reduce non-radiative voltage losses by up to several tens of millivolts., Funding Agencies|Leverhulme Trust [ECF-2022-445]; UK Engineering and Physical Sciences Research Council (EPSRC) Application Targeted and Integrated Photovoltaics (ATIP) project [EP/T028513/1]; UK EPSRC [EP/L016702/1]; EPSRC [EP/W017091/1]; National Natural Science Foundation of China [521253, 22005347]; Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the Research Training School "Molecular biradicals: Structure, properties and reactivity" [GRK2112]; Bavarian Ministry of the Environment and Consumer Protection, the Bavarian Network "Solar Technologies Go Hybrid"; China Scholarship Council (CSC); Research Grant Council of Hong Kong [14303519]

Although massive progress in power conversion efficiencies (PCEs) has been made on organic solar cells (OSCs), the challenge remains to scale up high-performance OSCs that are compatible with industrial production conditions, such as post-treatment-insensitive, non-halogenated solvent, large-area printing, processing under atmospheric environment. In this study, two A-D-A-D-A type oligomers, named 5BDDBDT-F and 5BDDBDT-Cl, were designed and synthesized to be incorporated into binary OSCs. Ex situ and in situ characterizations were performed to reveal the underlying working mechanisms. The two-phase transitions: liquid-to-liquid and liquid-to-solid can be synergistically tailored to promote the molecular arrangement of the binary blend. Benefiting from the enhanced crystallinity, the oligomer can act as a bridging linker to rehabilitate the interfacial defects to reduce the trap-assisted recombination losses and thus the non-radiative recombination losses. As a result, using non-halogenated solvent (o-xylene), the best-performing OSCs with PCEs of 18.32% with a VOC of 0.850 V, an FF of 79.15% were achieved based on the PM6:5BDDBDT-F:BTP-eC9 ternary OSCs, and 18.43% with a VOC of 0.854 V, an FF of 79.29% were obtained based on PM6:5BDDBDT-Cl:BTP-eC9 ternary OSCs without any post-processing. More importantly, it is noteworthy that the large-area (1 cm2) blade coated devices based on PM6:5BDDBDT-F:BTP-eC9 and PM6:5BDDBDT-Cl:BTP-eC9, processed using non-halogenated solvent in an open-air environment without thermal-annealing treatment, obtained high PCE values of 17.11% and 17.06%, respectively, which are among the highest PCE values of blade-coated OSCs in open air. This study demonstrated an efficient strategy of controlling crystallization kinetics to improve the material crystallinity, as an effective guideline for achieving high photovoltaic performance in printing ternary OSCs, pushing the OSCs towards future manufacturing. Two novel oligomers boost the 1 cm2 devic

Electronic devices based on tin halide perovskites often exhibit a poor operational stability. Here, we report an additive engineering strategy to realize high-performance and stable field-effect transistors (FETs) based on 3D formamidinium tin iodide (FASnI(3)) films. By comparatively studying the modification effects of two additives, i.e., phenethyl-ammonium iodide and 4-fluoro-phenyl-ethyl-ammonium iodide via combined experimental and theoretical investigations, we unambiguously point out the general effects of phenethyl-ammonium (PEA) and its fluorinated derivative (FPEA) in enhancing crystallization of FASnI(3) films and the unique role of fluorination in reducing structural defects, suppressing oxidation of Sn2+ and blocking oxygen and water involved defect reactions. The optimized FPEA-modified FASnI(3) FETs reach a record high field-effect mobility of 15.1 cm(2)/(V center dot s) while showing negligible hysteresis. The devices exhibit less than 10% and 3% current variation during over 2 h continuous bias stressing and 4200-cycle switching test, respectively, representing the best stability achieved so far for all Sn-based FETs.

All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5-Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5-Y5. The drying process of PBDBT:PF5-Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution., Funding Agencies|Knut and Alice Wallenberg foundation [2017.0186, 2016.0059]; Swedish Government Research Area in Materials Science on Functional Materials at Linkoeping University [200900971]; China Scholarship Council (CSC) [201708370115]; Swedish Research Council; Swedish Energy Agency; National Natural Science Foundation of China [21903017]

Organic photovoltaics (OPVs) have achieved great progress in recent years due to delicately designed non-fullerene acceptors (NFAs). Compared with tailoring of the aromatic heterocycles on the NFA backbone, the incorporation of conjugated side-groups is a cost-effective way to improve the photoelectrical properties of NFAs. However, the modifications of side-groups also need to consider their effects on device stability since the molecular planarity changes induced by side-groups are related to the NFA aggregation and the evolution of the blend morphology under stresses. Herein, a new class of NFAs with localisomerized conjugated side-groups are developed and the impact of local isomerization on their geometries and device performance/stability are systematically investigated. The device based on one of the isomers with balanced side- and terminal-group torsion angles can deliver an impressive power conversion efficiency (PCE) of 18.5%, with a low energy loss (0.528 V) and an excellent photo- and thermal stability. A similar approach can also be applied to another polymer donor to achieve an even higher PCE of 18.8%, which is among the highest efficiencies obtained for binary OPVs. This work demonstrates the effectiveness of applying local isomerization to fine-tune the side-group steric effect and non-covalent interactions between side-group and backbone, therefore improving both photovoltaic performance and stability of fused ring NFA-based OPVs., Funding Agencies|APRC Grant of the City University of Hong Kong; Innovation and Technology Commission of Hong Kong; Environment and Ecology Bureau of Hong Kong; Research Grants Council of Hong Kong [9380086, 9610508]; US Office of Naval Research [GHP/018/20SZ, MRP/040/21X]; Shen zhen Science and Technology Program [202020164]; Guangdong Major Project of Basic and Applied Basic Research [11307621, 11316422, N00014-20-1-2191]; Guangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials [C6023-19GF]; Office of Science, Office of Basic Energy Sciences, of the US Department of Energy [SGDX20201103095412040]; [2019B030302007]; [2019B121205002]; [DE-AC02-05CH11231]

Quasi-two-dimensional(2D) Pb-Sn mixed perovskites showgreat potential in applications of single and tandem photovoltaicdevices, but they suffer from low efficiencies due to the existenceof horizontal 2D phases. Here, we obtain a record high efficiencyof 18.06% based on 2D & LeftAngleBracket;n & RightAngleBracket; = 5 Pb-Sn mixed perovskites (iso-BA(2)MA(4)(Pb x Sn1-x )(5)I-16, x =0.7), by optimizing the crystal orientation through a regulation ofthe Pb/Sn ratio. We find that Sn-rich precursors give rise to a mixtureof horizontal and vertical 2D phases. Interestingly, increasing thePb content can not only entirely suppress the unwanted horizontal2D phase in the film but also enhance the growth of vertical 2D phases,thus significantly improving the device performance and stability.It is suggested that an increase of the Pb content in the Pb-Snmixed systems facilitates the incorporation of iso-butylammonium (iso-BA(+)) ligands in verticallyoriented perovskites because of the reduced lattice strain and increasedinteraction between the organic ligands and inorganic framework. Ourwork sheds light on the optimal conditions for fabricating stableand efficient 2D Pb-Sn mixed perovskite solar cells.

Solution-processed top electrodes using metallic nanoparticles have great potential in the high-throughput large-scale industrialization of organic solar cells (OSCs). To overcome poor reflectance, severe conditions of post-treatments, and unclear bottom-up formation mechanisms from nanoscale materials to bulk electrode films, we propose a compact-packing-enabled fabrication approach for stacking and then sintering metallic nanoparticles to become very efficient top electrodes with high conductivity and high broadband reflectance. We establish the formation mechanism in which spray-coated silver nanoparticle (AgNP) electrodes ligated by gallic acid (GA) form well-dispersed compactly packed structures during the stacking. Featuring the self-packing ability of AgNPs and a much higher space proportion of silver, GA-assisted AgNPs with a uniform distribution of particle size and superior storage stability form high-quality AgNP films in low-temperature sintering. Finally, attributing to the superior electrical and optical properties, and facile post-treatment of electrodes, the fully solution-processed OSCs with the GA-assisted AgNP electrodes achieve a record high efficiency of 14.69% for large-area devices (≥1 cm2).

Embedding submicrocavities is an effective approach to improve the light out-coupling efficiency (LOCE) for planar perovskite light-emitting diodes (PeLEDs). In this work, we employ phenethylammonium iodide (PEAI) to trigger the Ostwald ripening for the downward recrystallization of perovskite, resulting in spontaneous formation of buried submicrocavities as light output coupler. The simulation suggests the buried submicrocavities can improve the LOCE from 26.8 to 36.2% for near-infrared light. Therefore, PeLED yields peak external quantum efficiency (EQE) increasing from 17.3% at current density of 114 mA cm−2 to 25.5% at current density of 109 mA cm−2 and a radiance increasing from 109 to 487 W sr−1 m−2 with low rolling-off. The turn-on voltage decreased from 1.25 to 1.15 V at 0.1 W sr−1 m−2. Besides, downward recrystallization process slightly reduces the trap density from 8.90 × 1015 to 7.27 × 1015 cm−3. This work provides a self-assembly method to integrate buried output coupler for boosting the performance of PeLEDs.[Figure not available: see fulltext.] © 2023, The Author(s).

All-polymer solar cells (All-PSCs) are considered the most promising candidate in achieving both efficient and stable organic photovoltaic devices, yet the field has rarely presented an in-depth understanding of corresponding device stability while efficiency is continuously boosted via the innovation of polymer acceptors. Herein, a ternary matrix is built for all-PSCs with optimized morphology, improved film ductility and importantly, boosted efficiency and better operational stability than its parental binary counterparts, as a platform to study the underlying mechanism. The target system PQM-Cl:PTQ10:PY-IT (0.8:0.2:1.2) exhibits an alleviated burn-in loss of morphology and efficiency under light soaking, which supports its promoted device lifetime. The comprehensive characterizations of fresh and light-soaked active layers lead to a clear illustration of opposite morphological and physical degradation direction of PQM-Cl and PTQ10, thus resulting in a delicate balance at the optimal ternary system. Specifically, the enlarging tendency of PQM-Cl and shrinking preference of PTQ10 in terms of phase separation leads to a stable morphology in their mixing phase; the hole transfer kinetics of PQM-Cl:PY-IT host is stabilized by incorporating PTQ10. This work succeeds in reaching a deep insight into all-PSC's stability promotion by a rational ternary design, which booms the prospect of gaining high-performance all-PSCs.

Organic A′-site ligand structure plays a crucial role in the crystal growth of 2D perovskites, but the underlying mechanism has not been adequately understood. This problem is tackled by studying the influence of two isomeric A′-site ligands, linear-shaped n-butylammonium (n-BA+) and branched iso-butylammonium (iso-BA+), on 2D perovskites from precursor to device, with a combination of in situ grazing-incidence wide-angle X-ray scattering and density functional theory. It is found that branched iso-BA+, due to the lower aggregation enthalpies, tends to form large-size clusters in the precursor solution, which can act as pre-nucleation sites to expedite the crystallization of vertically oriented 2D perovskites. Furthermore, iso-BA+ is less likely to be incorporated into the MAPbI3 lattice than n-BA+, suppressing the formation of unwanted multi-oriented perovskites. These findings well explain the better device performance of 2D perovskite solar cells based on iso-BA+ and elucidate the fundamental mechanism of ligand structural impact on 2D perovskite crystallization.

Currently, nearly all high-efficiency organic photovoltaic devices use donor polymers based on the benzo-dithiophene (BDT) unit. To diversify the choices of building blocks for high-performance donor polymers, the use of benzo-difuran (BDF) units is explored, which can achieve reduced steric hindrance, stronger molecular packing, and tunable energy levels. In previous research, the performance of BDF-based devices lagged behind those of BDT-based devices. In this study, a high efficiency (18.4%) is achieved using a BDF-based polymer donor, which is the highest efficiency reported for BDF donor materials to date. The high efficiency is enabled by a donor polymer (D18-Fu) and the aid of a solid additive (2-chloronaphthalene), which is the isomer of the commonly used additive 1-chloronaphthalene. These results revealed the significant effect of 2-chloronaphthalene in optimizing the morphology and enhancing the device parameters. This work not only provides a new building block that can achieve an efficiency comparable to dominant BDT units but also proposes a new solid additive that can replace the widely used 1-chloronaphthalene additive.

Tuning the properties of non-fullerene acceptors (NFAs) through halogenation, including fluorination and chlorination, represents one of the most promising strategies to boost the performance of organic solar cells (OSCs). However, it remains unclear how the F and Cl choice influences the molecular packing and performance between small-molecule and polymeric acceptors. Here, a series of small-molecule and polymeric acceptors with different amounts and types of halogenation is synthesized, and the effects of fluorination and chlorination between small-molecule and polymeric acceptors are investigated. It is found that chlorinated small-molecule acceptors lead to longer exciton diffusion length and better performance compared to the corresponding fluorinated ones, which attributes to their stronger intermolecular packing mode. For polymer acceptors, in contrast, the fluorinated polymers achieve a denser packing mode and better performance, because chlorinated polymers exhibit reduced intrachain conjugation between end group moieties and linker units. This study demonstrates different halogenation effects on the packing modes and performances for small-molecule and polymeric acceptors, which provides important guidance for the molecule design of high-performance acceptors for OSCs.

Fullerene acceptors typically possess excellent electron-transporting properties and can work as guest components in ternary organic solar cells to enhance the charge extraction and efficiencies. However, conventional fullerene small molecules typically suffer from undesirable segregation and dimerization, thus limiting their applications in organic solar cells. Herein we report the use of a poly(fullerene-alt-xylene) acceptor (PFBO-C12) as guest component enables a significant efficiency increase from 16.9% for binary cells to 18.0% for ternary all-polymer solar cells. Ultrafast optic and optoelectronic studies unveil that PFBO-C12 can facilitate hole transfer and suppress charge recombination. Morphological investigations show that the ternary blends maintain a favorable morphology with high crystallinity and smaller domain size. Meanwhile, the introduction of PFBO-C12 reduces voltage loss and enables all-polymer solar cells with excellent light stability and mechanical durability in flexible devices. This work demonstrates that introducing polyfullerenes as guest components is an effective approach to achieving highly efficient ternary all-polymer solar cells with good stability and mechanical robustness.

Although the electroluminescent performances of perovskite light-emitting diodes (PeLEDs) are continuously improved through defect management strategies, the complicated design of passivation ligands brings great challenges to the rational defect-annihilation process. Herein, considering the bonding strength with uncoordinated Pb2+, the methoxy group with strong electron donating ability is introduced to commonly used phenethylammonium ligand as an efficient additive, namely 4-methoxy-phenethylammonium iodide (4-MeO-PEAI), to facilitate passivation process in perovskite light-emitting materials. It is demonstrated that the 4-MeO-PEAI agent substantially increases the crystal orientation, enlarges the crystalline grain size, and mitigates the deep-level trap centers through strong bonding between the methoxy group with unpaired Pb2+ ions. The external quantum efficiencyvalue of the PeLEDs with optimized passivation reaches a maximum of 21.6%, with an emission peak of 790 nm. In addition, a nearly threefold increase of the operational half-lifetime T50 of the 4-MeO-PEAI-mediated devices is observed as compared to the reference sample. Further theoretical calculation results suggest that the adhesion of the ligands on perovskite surface via vacancies leads to an increased dissociation barrier of perovskite; thus, ameliorating the degradation of the PeLEDs under electric field. The findings provide an effective design strategy of the passivation agents to produce high-performance perovskite-based optoelectronics devices.

State-of-the-art n-i-p perovskite solar cells (PSCs) suffer from stability issues due to ionic interdiffusion. Herein, by enlarging the indacenodithiophene pi-bridge donor (D ') to combine with the methoxy triphenylamine donor (D) and benzothiadiazole acceptor (A), three linear molecules termed L1, L2 and L3 with a D-A-D '-A-D structure are developed as dopant-free hole transport materials (HTMs). The pi-bridge extension with active sites for coordination leverages the intramolecular dipole effect and intermolecular packing effect, resulting in a conformally bonded ultrathin interface with compact and uniform coverage (similar to 60 nm) to retard iodine migration and protect the buried perovskite. The unencapsulated L3-PSC (ITO/SnO2/perovskite/L3/MoO3/Au) achieved an impressive PCE of 22.61% (certified 21.79%, 0.0525 cm(2)). Ultrafast laser spectroscopy reveals that L-series molecules have a sequential reduction of photoexcited energy disorder to illustrate the structure-performance-stability relationship. L3-PSC maintains over 85% of the initial efficiency after 500 h at 85 degrees C maximum power point tracking (MPP) and enables the possibility of using small molecules to stabilize n-i-p PSCs.

All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5-Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5-Y5. The drying process of PBDBT:PF5-Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution., Funding Agencies|Knut and Alice Wallenberg foundation [2017.0186, 2016.0059]; Swedish Government Research Area in Materials Science on Functional Materials at Linkoeping University [200900971]; China Scholarship Council (CSC) [201708370115]; Swedish Research Council; Swedish Energy Agency; National Natural Science Foundation of China [21903017]

All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5–Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5–Y5. The drying process of PBDBT:PF5–Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution.

All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5–Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5–Y5. The drying process of PBDBT:PF5–Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution.

All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5–Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5–Y5. The drying process of PBDBT:PF5–Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution.

Non-fullerene acceptors (NFAs) have enabled power conversion efficiencies exceeding 19% in organic solar cells (OSCs). However, the open-circuit voltage of OSCs remains low relative to their optical gap due to excessive non-radiative recombination, and this now limits performance. Here, an important aspect of OSC design is considered, namely management of the triplet exciton population formed after non-geminate charge recombination. By comparing the blends PM6:Y11 and PM6:Y6, it is shown that the greater crystallinity of the NFA domains in PM6:Y11 leads to a higher rate of triplet-triplet annihilation (TTA). This is attributed to the four times larger ground state dipole moment of Y11 versus Y6, which improves the long range NFA out-of-plane ordering. Since TTA converts a fraction of the non-emissive triplet states into bright singlet states, it has the potential to reduce non-radiative voltage losses. Through a kinetic analysis of the recombination processes under 1-Sun illumination, a framework is provided for determining the conditions under which TTA may improve OSC performance. If these could be satisfied, TTA has the potential to reduce non-radiative voltage losses by up to several tens of millivolts., Funding Agencies|Leverhulme Trust [ECF-2022-445]; UK Engineering and Physical Sciences Research Council (EPSRC) Application Targeted and Integrated Photovoltaics (ATIP) project [EP/T028513/1]; UK EPSRC [EP/L016702/1]; EPSRC [EP/W017091/1]; National Natural Science Foundation of China [521253, 22005347]; Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the Research Training School "Molecular biradicals: Structure, properties and reactivity" [GRK2112]; Bavarian Ministry of the Environment and Consumer Protection, the Bavarian Network "Solar Technologies Go Hybrid"; China Scholarship Council (CSC); Research Grant Council of Hong Kong [14303519]

The simple ester side-chains strategy has been an effective approach in fine regulating electronic levels, intermolecular interaction, and aggregation morphology of organic photovoltaic materials, which makes for promoting the photovoltaic performance of organic solar cells (OSCs). Herein, two novel D-A conjugated polymers, namely PBQxBE and PBQxTE, are designed and synthesized, derived from an alkylthiothiophene benzodithiophene (BDTTS) as donor moiety, thiophene as the π-bridges, and an identical molecular skeleton but different side chains based on quinoxaline (Qx) as acceptor units. The PBQxBE with ester engineered benzene side chains on the Qx unit exhibits better molecular flatness, stronger intermolecular interaction, and higher hole mobility than the analogous PBQxTE with ester engineered thiophene side chains. After combined with polymer acceptor PIDTC-T, the blend film of PBQxBE:PIDTC-T presented higher and balanced hole/electron mobility, better favorable aggregation morphology, as well as less charge carrier recombination. Thus, the all-polymer solar cells (all-PSCs) based on PBQxBE:PIDTC-T delivered a power conversion efficiency (PCE) of 10.17% with simultaneously increased basic parameters, which is much higher than that of 7.40% for the PBQxTE-based ones. The PCE of 10.17% is by far the highest values reported for all-PSCs from the Qx-based polymers as donor. The results demonstrate that the ester side-chains engineering of Qx-based polymers is an effective strategy to improve their photovoltaic performance of all-PSCs. © 2021 Elsevier B.V.

All-polymer solar cells (APSCs) are one of the most promising types of application-oriented photovoltaic technologies because they are operationally and mechanically stable; however, their low power conversion efficiency (PCE) restricts the core competitiveness against other types of solar cells. Besides, poor insight of mechanical performance, such as ductility, has been revealed for cutting-edge APSCs. Herein, we chose two well miscible polymer donors, PM6 and J71, and achieved a PCE of 16.52% for APSCs in a ternary blend with PY-IT and 15.74% for air-processed devices. The improvement is enabled by effective energy transfer, tuned crystallinity, and improved phase separation, which resulted in faster charge transfer and more balanced charge transport, suppressed exciton recombination, and more efficient charge extraction. Furthermore, the good miscibility between two donors enabled the target to have well-maintained film morphology without damaging the initial nanoscale network, bringing comparable film ductility. Last, the inner structure-property relationship of photovoltaic and morphological parameters, and film ductility was illustrated by a correlation study.

Unidirectionally aligned nanorods (NRs) are of great importance for different applications, including displays, lighting, and photodetectors. Recently, many alignment techniques were studied to align quantum rods (QRs). However, the brightness of these films, due to the limited concentration of aligned quantum rods in the film, is not enough for their implementation as brightness enhancement films (BEFs) in displays. This can be ascribed to the poor miscibility of quantum rods in polymer and strong concentration dependence of the polarized emission. The ligands of NR are very important for the alignment and brightness. In this article, we proposed a ligand combination comprising T-shape promesogenic phosphonic acid, which on being photoaligned provides mutually parallel alignment of the quantum rods. The T-shape ligands enable the fabrication of hybrid films with a QRs concentration as high as 10 wt.%`-20 wt.% retaining high brightness and luminescence polarization property. Later, we used these films in the in-plane switching (IPS) display backlight that shows the color gamut up to 121% of national television system committee (NTSC) (CIE1931), liquid-crystal display (LCD) efficiency up to 7.9%, power efficacy 103 ± 2 nits/W, and the high brightness of ∼ 550 ± 10 nits. Thus, the proposed ligands can be used for the alignment of a variety of nanorods.[Figure not available: see fulltext.] © 2021, Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature.

Electron donors and acceptors in organic solar cells (OSCs) shall strike a favorable vertical phase separation that acceptors and donors have sufficient contact and gradient accumulation near the cathodes and anodes, respectively. Random mixing of donors/acceptors at surface will result in charge accumulation and severe recombination for low carrier-mobility organic materials. However, it is challenging to tune the vertical distribution in bulk-heterojunction films as they are usually made from a well-mixed donor/acceptor solution. Here, for the first time, it presents with solid evidence that the commonly used 1-chloronaphthalene (CN) additive can tune the donor/acceptor vertical distribution and establish the mechanism. Different from the previous understanding that ascribed the efficiency enhancement brought by CN to the improved molecular stacking/crystallization, it is revealed that the induced vertical distribution is the dominant factor leading to the significantly increased performance. Importantly, the vertical distribution tunability is effective in various hot nonfullerene OSC systems and creates more channels for the collection of dissociated carriers at corresponding organic/electrode interfaces, which contributes the high efficiency of 18.29%. This study of the material vertical distribution and its correlation with molecular stacking offers methods for additives selection and provides insights for the understanding and construction of high-performance OSCs. © 2022 Wiley-VCH GmbH

2D–3D mixed tin halide perovskites are outstanding candidate materials for lead-free perovskite solar cells (PSCs) due to their improved stability and decreased trap density in comparison with their pure 3D counterparts. However, the mixture of multiple phases may lead to poor charge transfer across the films and limit the device efficiency. Here, a stacked quasi-2D (down)–3D (top) double-layered structure in perovskite films prepared via vacuum treatment is demonstrated, which can result in a planar bilayer heterojunction. In addition, it is found that the introduction of guanidinium thiocyanate (GuaSCN) additive can improve the crystallinity and carrier mobility in the 2D perovskite layer and passivate defects in the whole film, leading to a long carrier lifetime (>140 ns) in photoluminescence measurements. As a result, the PSCs show a high open circuit voltage (VOC) up to 1.01 V with a voltage loss of only 0.39 V, which represents the record values ever reported for tin-based PSCs. The champion device exhibits a power conversion efficiency (PCE) of 13.79% with decent stability, retaining 90% of the initial PCE for 1200 h storage in N2-filled glovebox.

Unidirectionally aligned nanorods (NRs) are of great importance for different applications, including displays, lighting, and photodetectors. Recently, many alignment techniques were studied to align quantum rods (QRs). However, the brightness of these films, due to the limited concentration of aligned quantum rods in the film, is not enough for their implementation as brightness enhancement films (BEFs) in displays. This can be ascribed to the poor miscibility of quantum rods in polymer and strong concentration dependence of the polarized emission. The ligands of NR are very important for the alignment and brightness. In this article, we proposed a ligand combination comprising T-shape promesogenic phosphonic acid, which on being photoaligned provides mutually parallel alignment of the quantum rods. The T-shape ligands enable the fabrication of hybrid films with a QRs concentration as high as 10 wt.%`-20 wt.% retaining high brightness and luminescence polarization property. Later, we used these films in the in-plane switching (IPS) display backlight that shows the color gamut up to 121% of national television system committee (NTSC) (CIE1931), liquid-crystal display (LCD) efficiency up to 7.9%, power efficacy 103 ± 2 nits/W, and the high brightness of ∼ 550 ± 10 nits. Thus, the proposed ligands can be used for the alignment of a variety of nanorods.[Figure not available: see fulltext.] © 2021, Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature.

The tuning of vertical morphology is critical and challenging for organic solar cells (OSCs). In this work, a high open-circuit voltage (VOC) binary D18-Cl/L8-BO system is attained while maintaining the high short-circuit current (JSC) and fill factor (FF) by employing 1,4-diiodobenzene (DIB), a volatile solid additive. It is suggested that DIB can act as a linker between donor or/and acceptor molecules, which significantly modifies the active layer morphology. The overall crystalline packing of the donor and acceptor is enhanced, and the vertical domain sizes of phase separation are significantly decreased. All these morphological changes contribute to exciton dissociation, charge transport, and collection. Therefore, the best-performing device exhibits an efficiency of 18.7% with a VOC of 0.922 V, a JSC of 26.6 mA cm−2, and an FF of 75.6%. As far as it is known, the VOC achieved here is by far the highest among the reported OSCs with efficiencies over 17%. This work demonstrates the high competence of solid additives with two iodine atoms to tune the morphology, particularly in the vertical direction, which can become a promising direction for future optimization of OSCs.

All-polymer solar cells (APSCs) are one of the most promising types of application-oriented photovoltaic technologies because they are operationally and mechanically stable; however, their low power conversion efficiency (PCE) restricts the core competitiveness against other types of solar cells. Besides, poor insight of mechanical performance, such as ductility, has been revealed for cutting-edge APSCs. Herein, we chose two well miscible polymer donors, PM6 and J71, and achieved a PCE of 16.52% for APSCs in a ternary blend with PY-IT and 15.74% for air-processed devices. The improvement is enabled by effective energy transfer, tuned crystallinity, and improved phase separation, which resulted in faster charge transfer and more balanced charge transport, suppressed exciton recombination, and more efficient charge extraction. Furthermore, the good miscibility between two donors enabled the target to have well-maintained film morphology without damaging the initial nanoscale network, bringing comparable film ductility. Last, the inner structure-property relationship of photovoltaic and morphological parameters, and film ductility was illustrated by a correlation study.

Cesium lead based all-inorganic perovskite solar cells (PSCs) are promising candidates for tandem solar cells owing to their favorable thermal stability and suitable bandgap. However, to exploit the advantage to the full, there is still huge room to reduce energy loss and enhance the V-OC. In this work, we developed low-temperature processed ZnO as an ETL alternative. Incorporation of PbX2 (X = I-, Cl-, and CH3COO-) was found to increase oxygen vacancies in ZnO, which not only promoted the growth of all-inorganic perovskite layer with improved morphology and orientational order, but also formed a favorable energy level alignment with the perovskite layer, thus facilitating charge extraction and suppressing charge recombination. Consequently, the CsPb(I1-xBrx)(3) PSCs based on PbX2:ZnO exhibited enhanced stability and performance. The efficiency was boosted from 17.64% to 20.04% with an improved fill factor of 84.14% and a V-OC of 1.28 V, being the highest V-OC among highly efficient (>20%) all-inorganic PSCs to date.

Rationally utilizing and developing synthetic units is of particular significance for the design of high-performance non-fullerene small-molecule acceptors (SMAs). Here, a thieno[3,2-b]pyrrole synthetic unit was employed to develop a set of SMAs (ThPy1, ThPy2, ThPy3 and ThPy4), by changing the number or the position of the pyrrole ring in the central core based on a standard SMA of IT-4Cl, compared to which the four thieno[3,2-b]pyrrole-based acceptors exhibit bathochromic absorption and upshifted frontier orbital energy level due to the strong electron-donating ability of pyrrole. As a result, the polymer solar cells (PSCs) of the four thieno[3,2-b]pyrrole-based acceptors yield higher open-circuit voltage and lower energy loss relative to those of the IT-4Cl-based device. What's more, ThPy3-based device achieves a power conversion efficiency (PCE) (15.3%) and an outstanding fill factor (FF) (0.771) that are superior to the IT-4Cl-based device (PCE = 12.6%, FF = 0.758). The ThPy4-based device realizes the lowest energy loss and the smallest optical band gap, and the ternary PSC device based on PM6:BTP-eC9:ThPy4 exhibits a PCE of 18.43% and a FF of 0.802. Overall, this work sheds light on the great potential of thieno[3,2-b]pyrrole-based SMAs in realizing low energy loss and high PCE.

Electron donors and acceptors in organic solar cells (OSCs) shall strike a favorable vertical phase separation that acceptors and donors have sufficient contact and gradient accumulation near the cathodes and anodes, respectively. Random mixing of donors/acceptors at surface will result in charge accumulation and severe recombination for low carrier-mobility organic materials. However, it is challenging to tune the vertical distribution in bulk-heterojunction films as they are usually made from a well-mixed donor/acceptor solution. Here, for the first time, it presents with solid evidence that the commonly used 1-chloronaphthalene (CN) additive can tune the donor/acceptor vertical distribution and establish the mechanism. Different from the previous understanding that ascribed the efficiency enhancement brought by CN to the improved molecular stacking/crystallization, it is revealed that the induced vertical distribution is the dominant factor leading to the significantly increased performance. Importantly, the vertical distribution tunability is effective in various hot nonfullerene OSC systems and creates more channels for the collection of dissociated carriers at corresponding organic/electrode interfaces, which contributes the high efficiency of 18.29%. This study of the material vertical distribution and its correlation with molecular stacking offers methods for additives selection and provides insights for the understanding and construction of high-performance OSCs. © 2022 Wiley-VCH GmbH

The morphology of organic solar cells (OSCs) is a core topic for reaching ultimate photovoltaic performance. Herein, we focused on the combination of two important morphology regulation strategies – ternary strategy and cosolvent engineering. Using an amorphous polymer acceptor BN-T as the third component, the PM6:BTP-eC11 and PM6:eC9 host binary systems, treated by the respective (o-xylene and 1-phenylnaphthalene solvent system and chlorobenzene and1,8-diiodooctane solvent system,both realized effective improvement in the power conversion efficiencies (PCEs). However, ex-situ morphological characterizations revealed these two systems experienced different ways of change in phase segregation and molecular packing, which cannot be understood by the current popular miscibility analysis. In this work, in-situ investigation was carried out upon the spin cast and thermal annealing processes. The time-resolved reflection spectroscopy technique showed that BN-T retained more PN in ternary films during the cast, thereby facilitating the eC11’s aggregation, and enlarging its domain size. In contrast, BN-T’s incorporation didn’t affect the DIO’s content in films, resulting in less separated morphology for eC9 based systems as predicted by the miscibility study. In addition to the state-of-the-art PCEs, this work provides an insightful understanding of the morphology evolution in ternary OSCs assisted by high-boiling solvent additive via in-situ investigation techniques.

Rationally utilizing and developing synthetic units is of particular significance for the design of high-performance non-fullerene small-molecule acceptors (SMAs). Here, a thieno[3,2-b]pyrrole synthetic unit was employed to develop a set of SMAs (ThPy1, ThPy2, ThPy3 and ThPy4) by changing the number or the position of the pyrrole ring in the central core based on a standard SMA of IT-4Cl, compared to which the four thieno[3,2-b]pyrrole-based acceptors exhibit bathochromic absorption and upshifted frontier orbital energy level due to the strong electron-donating ability of pyrrole. As a result, the polymer solar cells (PSCs) of the four thieno[3,2-b]pyrrole-based acceptors yield higher open-circuit voltage and lower energy loss relative to those of the IT-4Cl-based device. What is more, the ThPy3-based device achieves a power conversion efficiency (PCE) (15.3%) and an outstanding fill factor (FF) (0.771) that are superior to the IT-4Cl-based device (PCE = 12.6%, FF = 0.758). The ThPy4-based device realizes the lowest energy loss and the smallest optical band gap, and the ternary PSC device based on PM6:BTP-eC9:ThPy4 exhibits a PCE of 18.43% and a FF of 0.802. Overall, this work sheds light on the great potential of thieno[3,2-b]pyrrole-based SMAs in realizing low energy loss and high PCE. Four heteroheptacene-based acceptors using thieno[3,2-b]pyrrole building block were developed for the first time, and all the four acceptors-based devices realized high performance and low energy loss., Funding Agencies|National Key Research and Development Program of China - Ministry of Science and Technology [2019YFA0705900]; Basic and Applied Research Major Programme of Guangdong Province [2019B030302007]; National Natural Science Foundation of China [91433202]; Shenzhen Technology and Innovation Commission through Shenzhen Fundamental Research Program [JCYJ20200109140801751]; Hong Kong Innovation and Technology Commission [ITC-CNERC14SC01]; Foshan-HKUST [FSUST19-CAT0202]; Hong Kong Research Grants Council (RIF project) [R6021-18]; Hong Kong Research Grants Council (CRF project) [C6023-19G]; Hong Kong Research Grants Council (GRF project) [16310019, 16310020]