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A new benzodithiophene (BDT)-based building block, 3-FBDT, was synthesized and incorporated into PBDB-T-2F to yield an eco-friendly (non-aromatic and non-halogenated) solvent-processible photovoltaic copolymer, PBDB-T-2F(3/4).

An asymmetric acceptor BTP-PhC6-C11 shows hydrogen bond assisted and tighter crystal packing and enhanced electronic coupling as compared with symmetric Y6 and BTP-PhC6, and organic solar cells based on PM1:BTP-PhC6-C11 realized a highest PCE of 18.33%.

A systematical study was presented via engineering the N-alkyl chains onto non-fullerene acceptors to manipulate their multiscale lamella self-assembly and intermixing with polymer donor towards an optimal bulk morphology.

Narrow bandgap (NBG) block copolymers are promising materials to realize single-material organic solar cells (SMOSCs) that combine high performance with minimized fabrication procedures.

The development of n-type organic semiconductors critically relies on the design and synthesis of highly electron-deficient building blocks with good solubility and small steric hindrance. We report here a strongly electron-deficient dithienylpyrazinediimide (TPDI) and its n-type semiconducting polymers. The pyrazine substitution leads to the resulting polymers with much lower-lying lowest unoccupied molecular orbital (LUMO) levels and improved backbone planarity compared to the reported dithienylbenzodiimide (TBDI)- and fluorinated dithienylbenzodiimide (TFBDI)-based polymer analogues, thus yielding n-type transport character with an electron mobility up to 0.44 cm

The development of n-type organic electrochemical transistors (OECTs) lags far behind their p-type counterparts. In order to address this dilemma, we report here two new fused bithiophene imide dimer (f-BTI2)-based n-type polymers with a branched methyl end-capped glycol side chain, which exhibit good solubility, low-lying LUMO energy levels, favorable polymer chain orientation, and efficient ion transport property, thus yielding a remarkable OECT electron mobility (μe ) of up to ≈10-2 cm2 V-1 s-1 and volumetric capacitance (C*) as high as 443 F cm-3 , simultaneously. As a result, the f-BTI2TEG-FT-based OECTs deliver a record-high maximum geometry-normalized transconductance of 4.60 S cm-1 and a maximum μC* product of 15.2 F cm-1 V-1 s-1 . The μC* figure of merit is more than one order of magnitude higher than that of the state-of-the-art n-type OECTs. The emergence of f-BTI2TEG-FT brings a new paradigm for developing high-performance n-type polymers for low-power OECT applications.

n-Type semiconducting polymers with high thermoelectric performance remain challenging due to the scarcity of molecular design strategy, limiting their applications in organic thermoelectric (OTE) devices. Herein, we provide a new approach to enhance the OTE performance of n-doped polymers by introducing acceptor-acceptor (A-A) type backbone bearing branched ethylene glycol (EG) side chains. When doped with 4-(2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzenamine (N-DMBI), the A-A homopolymer PDTzTI-TEG exhibits n-type electrical conductivity (σ) up to 34 S cm

All-polymer solar cells (all-PSCs) have achieved tremendous progress due to the recent advances of polymerized small molecule acceptors (PSMAs) and their power conversion efficiencies (PCEs) have reached over 14%. However, the practical applications of all-PSCs are still severely restricted by the lack of PSMAs with a broad absorption spectrum, high electron mobility, low energy loss, and good batch-to-batch reproducibility. Herein, a multi-selenophene-containing PSMA, namely PFY-3Se, based on a selenophene-fused SMA framework and a selenophene π-spacer was designed and developed. Compared to its thiophene analog PFY-0Se, PFY-3Se possesses a significantly red-shifted absorption (~30 nm), increased electron mobility, and improved intermolecular aggregation and packing. When matched with polymer donor PBDB-T, the PFY-3Se-based all-PSCs achieved an impressive PCE of 15.1% with both high short-circuit current density of 23.6 mA cm-2 and high fill factor of 0.737, and a low energy loss, which are among the best values in all-PSCs field reported so far and much better than those of thiophene analogs (PCE=13.0%). More importantly, PFY-3Se maintains similarly good batch-to-batch properties which is very helpful for realizing reproducible device performance. This is the first reported and also is very rare for the PSMAs so far which provides a potential candidate for efficient all-PSCs toward practical applications.

Tuning molecular aggregation via structure design to manipulate the film morphology still remains as a challenge for polymer solar cells based on unfused non-fullerene acceptors (UF-NFAs). Herein, a strategy was developed to modulate the aggregation patterns of UF-NFAs by systematically varying the π-bridge (D) unit and central core (A') unit in A-D-A'-D-A framework (A and D refer to electron-withdrawing and electron-donating moieties, respectively). Specifically, the quantified contents of H- or J-aggregation and crystallite disorder of three UF-NFAs (BDIC2F, BCIC2F, and TCIC2F) were analyzed via UV/Vis spectrometry and grazing incidence X-ray scattering. The results showed that the H-aggregate-dominated BCIC2F with less crystallite disorder exhibited a more favorable blend morphology with polymer donor PBDB-T (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c']dithiophene-4,8-dione)]) relative the other two UF-NFAs, resulting in improved exciton dissociation and charge tranport. Consequently, photovoltaic devices based on BCIC2F delivered a promising power conversion efficiency of 12.4 % with an exceptionally high short-circuit current density of 22.1 mA cm-2 .

Intramolecular Cl-S non-covalent interaction is introduced to modify molecular backbone of a benzodithiophene terthiophene rhodamine (BTR) benchmark structure, helping planarize and rigidify the molecular framework for improving charge transport. Theoretical simulations and temperature-variable NMR experiments clearly validate the existence of Cl-S non-covalent interaction in two designed chlorinated donors and explain its important role in enhancing planarity and rigidity of the molecules for enhancing their crystallinity. The asymmetric isomerization of side-chains further optimizes the molecular orientation and surface energy to strike a balance between its crystallinity and miscibility. This carefully manipulated molecular design helps result in increased carrier mobility and suppressed charge recombination to obtain simultaneously enhanced short-circuit current (J

Ruddlesden–Popper phase 2D perovskite solar cells (PSCs) exhibit improved lifetime while still facing challenges such as phase alignment and up-scaling to module-level devices. Herein, polyelectrolytes are explored to tackle this issue. The contact between perovskite and hole-transport layer (HTL) is important for decreasing interfacial non-radiative recombination and scalable fabrication of uniform 2D perovskite films. Through exploring compatible butylamine cations, we first demonstrate poly(3-(4-carboxybutyl)thiophene-2,5-diyl)-butylamine (P3CT-BA) as an efficient HTL for 2D PSCs due to its great hydrophilicity, relatively high hole mobility and uniform surface. More importantly, the tailored P3CT-BA has an anchoring effect and acts as the buried passivator for 2D perovskites. Consequently, a best efficiency approaching 18¿% was achieved and we further first report large-area (2×3 cm2, 5×5 cm2) 2D perovskite minimodules with an impressive efficiency of 14.81¿% and 11.13¿%, respectively.

n-Type polymers with deep-positioned lowest unoccupied molecular orbital (LUMO) energy levels are essential for enabling n-type organic thin-film transistors (OTFTs) with high stability and n-type organic thermoelectrics (OTEs) with high doping efficiency and promising thermoelectric performance. Bithiophene imide (BTI) and its derivatives have been demonstrated as promising acceptor units for constructing high-performance n-type polymers. However, the electron-rich thiophene moiety in BTI leads to elevated LUMOs for the resultant polymers and hence limits their n-type performance and intrinsic stability. Herein, we addressed this issue by introducing strong electron-withdrawing cyano functionality on BTI and its derivatives. We have successfully overcome the synthetic challenges and developed a series of novel acceptor building blocks, CNI, CNTI, and CNDTI, which show substantially higher electron deficiencies than does BTI. On the basis of these novel building blocks, acceptor-acceptor type homopolymers and copolymers were successfully synthesized and featured greatly suppressed LUMOs (-3.64 to -4.11 eV) versus that (-3.48 eV) of the control polymer PBTI. Their deep-positioned LUMOs resulted in improved stability in OTFTs and more efficient n-doping in OTEs for the corresponding polymers with a highest electrical conductivity of 23.3 S cm

Organic photovoltaic (OPV) cells have highly tunable light-response ranges, enabling them to achieve high power conversion efficiencies (PCEs) in various scenarios. Until now, most studies of these devices have focused on developing highly efficient OPV cells under the standard AM 1.5G solar radiation. However, light harvesting under indoor lighting conditions is also important, and OPV cells have successfully demonstrated their potential for indoor power generation. To meet the requirements of the rapid development of the Internet of Things (IoT), it is very important to develop highly efficient OPV cells for both indoor and outdoor applications. Here, we report the design and synthesis of a non-fullerene acceptor HDO-4Cl, which has a well-matched absorption spectrum for both solar and indoor-light radiation spectra. As a result, these OPV cells based on PBDB-TF:HDO-4Cl yield a good PCE of 15.5% under AM 1.5G solar illumination and an impressive PCE of 23.4% under light-emitting dioxide illumination at 1000 lux. Our results suggest that OPV cells have great potential for use in various application scenarios.

Nonfullerene acceptors (NFAs) have played an important role in the development of organic solar cells. However, the optical absorption of most NFAs is limited within 600–900 nm, prohibiting further...

Developing dopant-free hole-transporting materials (HTMs) for high-performance perovskite solar cells (PVSCs) has been a very active research topic in recent years since HTMs play a critical role in optimizing interfacial charge carrier kinetics and in turn determining device performance. Here, a novel dendritic engineering strategy is first utilized to design HTMs with a D-A type molecular framework, and diphenylamine and/or carbazole is selected as the building block for constructing dendrons. All HTMs show good thermal stability and excellent film morphology, and the key optoelectronic properties could be fine-tuned by varying the dendron structure. Among them, MPA-Cz-BTI and MCz-Cz-BTI exhibit an improved interfacial contact with the perovskite active layer, and non-radiative recombination loss and charge transport loss can be effectively suppressed. Consequently, high power conversion efficiencies (PCEs) of 20.8% and 21.35% are achieved for MPA-Cz-BTI and MCz-Cz-BTI based devices, respectively, accompanied by excellent long-term storage stability. More encouragingly, ultrahigh fill factors of 85.2% and 83.5% are recorded for both devices, which are among the highest values reported to date. This work demonstrates the great potential of dendritic materials as a new type of dopant-free HTMs for high-performance PVSCs with excellent FF.

Although halogenation has been widely regarded as an effective approach to adjust the properties of organic semiconductors, systematic investigation on the comparison of nonhalogenated and halogenated polymer acceptors only received minor attention in all-polymer solar cell (all-PSC) community. Herein, we report three IDIC-based narrow band gap polymer acceptors, PIDIC2T, PIDIC2T2F, and PIDIC2T2Cl, which are composed of IDIC-C16 building blocks as acceptor units, linking pristine bithiophene, fluorinated bithiophene, or chlorinated bithiophene as donor units. Although these three polymer acceptors exhibit nearly identical lowest unoccupied molecular orbital (LUMO) levels of ca. -3.87 eV with a similar optical band gap of ca. 1.54 eV, we found that different halogen species significantly affect the electron mobility and thin-film morphology of the polymer acceptors. All-PSCs were fabricated by pairing three polymer acceptors with a PBDB-T polymer donor, while PIDIC2T2Cl delivered a highest power conversion efficiency (PCE) of 5.34% due to its favorable bulk morphology with smaller root-mean-square (rms) roughness values, which induce the relatively more balanced charge carrier mobilities. By blending the fluorinated analogue of PBDB-T, PM6, further improved

Nonradiative recombination energy loss (ΔE3) plays a key role in enhancing device efficiencies for polymer solar cells (PSCs). Until now, there is no clear resolution for reducing ΔE3 via molecular...

A hybrid welding technique formed by combining keyhole plasma arc welding (KPAW) and pulsed gas metal arc welding (GMAW-P) is characterized by the complex interactions of the arc, droplet, keyhole, and weld pool. With the help of a high-speed video camera, zirconia particles, and a thermal camera, the complex interactive phenomena of the hybrid KPAW–GMAW-P process was analyzed. Owing to the formation of a direct-current path between the KPAW cathode (tungsten electrode) and the GMAW anode (welding wire), the ionized plasma arc was extended to the GMA side, causing an expansion of the GMA. The current at the GMAW droplet was diverged; thus, the Lorentz force promoted a more stable one pulse one droplet metal transfer mode compared with that of GMAW-P. The strong backward flow from the keyhole was suppressed because of the pull-push flow pattern on the top surface of the weld pool be-tween the two arcs. As the heat and molten metal in the weld pool were transported from the region near the GMA (high temperature) to the region near the plasma arc (low temperature), the weld pool temperature decreased.

The dominated hole transport material (HTM) used in state-of-the-art perovskite solar cells (PSCs) is Spiro-OMeTAD, which needs to be doped to improve its conductivity and mobility. The inevitable instability induced by deliquescent dopants and the necessary oxidation process in air hinders the commercialization of this technology. Here, an alloy strategy using two conjugated polymers with highly similar structures but different crystallinities for dopant-free HTM and high-performance PSCs has been demonstrated. We found that the polymeric packing and crystallinity of a polymer alloy could be regulated finely by blending the polymer PM6 and our developed polymer PMSe, which exhibits a shorter π-π stacking distance due to the improved planarity of the polymer backbone with strong C═O···Se noncovalent interactions. The structure-property relationship of the polymer alloy is investigated by theoretical and experimental analyses. The optimized PSCs using the polymer alloy HTM without any ionic dopants feature an excellent power conversion efficiency of 24.53% and a high open circuit voltage (

Organic electrochemical transistors (OECTs) have the potential to revolutionize the field of organic bioelectronics. To date, most of the reported OECTs include p-type (semi-)conducting polymers as the channel material, while n-type OECTs are yet at an early stage of development, with the best performing electron-transporting materials still suffering from low transconductance, low electron mobility, and slow response time. Here, the high electrical conductivity of multi-walled carbon nanotubes (MWCNTs) and the large volumetric capacitance of the ladder-type pi-conjugated redox polymer poly(benzimidazobenzophenanthroline) (BBL) are leveraged to develop n-type OECTs with record-high performance. It is demonstrated that the use of MWCNTs enhances the electron mobility by more than one order of magnitude, yielding fast transistor transient response (down to 15 ms) and high mu C* (electron mobility x volumetric capacitance) of about 1 F cm(-1) V-1 s(-1). This enables the development of complementary inverters with a voltage gain of >16 and a large worst-case noise margin at a supply voltage of Funding Agencies|Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2016-03979, 2020-03243]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [14-0074]; AForsk [18-313, 19-310]; Olle Engkvists Stiftelse [204-0256]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat- LiU 2009-00971]; European Commission through the FET-OPEN project MITICS [GA-964677]; VINNOVAVinnova [2020-05223]; National Research Foundation of KoreaNational Research Foundation of Korea [NRF-2019R1A2C2085290, 2019R1A6A1A11044070]

Introduction of filler materials into organic solar cells (OSCs) are a promising strategy to improve device performance and thermal/mechanical stability. However, the complex interactions between the state-of-the-art OSC materials and filler require careful selection of filler materials and OSC fabrication to achieve lower cost and improved performance. In this work, the introduction of a natural product betulin-based insulating polymer as filler in various OSCs is investigated. Donor-acceptor-insulator ternary OSCs are developed with improved open-circuit voltage due to decreased trap-assisted recombination. Furthermore, filler-induced vertical phase separation due to mismatched surface energy can strongly affect charge collection at the bottom interface and limit the filler ratio. A quasi-bilayer strategy is used in all-polymer systems to circumvent this problem. Herein, the variety of filler materials in OSCs to biomass is broadened, and the filler strategy is made a feasible and promising strategy toward highly efficient, eco, and low-cost OSCs. Funding Agencies|Knut and Alice Wallenberg Foundation (KAW) through the Wallenberg Wood Science Center; Swedish Energy Agency [45411-1]; Swedish Research Council [2016-05498, 2016-05990, 2020-04538, 2018-06048]; STINT grant [CH2017-7163]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]

Intramolecular noncovalent interactions (INIs) have served as a powerful strategy for accessing organic semiconductors with enhanced charge transport properties. Herein, we apply the INI strategy for developing dopant-free hole-transporting materials (HTMs) by constructing two small-molecular HTMs featuring an INI-integrated backbone for high-performance perovskite solar cells (PVSCs). Upon incorporating noncovalent S⋅⋅⋅O interaction into their simple-structured backbones, the resulting HTMs, BTORA and BTORCNA, showed self-planarized backbones, tuned energy levels, enhanced thermal properties, appropriate film morphology, and effective defect passivation. More importantly, the high film crystallinity enables the materials with substantial hole mobilities, thus rendering them as promising dopant-free HTMs. Consequently, the BTORCNA-based inverted PVSCs delivered a power conversion efficiency of 21.10 % with encouraging long-term device stability, outperforming the devices based on BTRA without S⋅⋅⋅O interaction (18.40 %). This work offers a practical approach to designing charge transporting layers with high intrinsic mobilities for high-performance PVSCs.

Eco-friendly polymer solar cells (eco-PSCs) based on aqueous-soluble conjugated materials have recently received great research attention. In this work, we report the development of an aqueous-processable C70-based fullerene derivative (PC71BO15) for eco-PSCs processed by water/ethanol co-solvents. The desirable aggregation behavior and enhanced light absorption ability of PC71BO15 have enabled the fabrication of PPDT2FBT-A:PC71BO15-based eco-PSCs with power conversion efficiencies (PCEs) of up to 2.51%, which is the highest value reported to date for aqueous-processed PSCs. These PPDT2FBT-A:PC71BO15 eco-PSCs exhibit significantly higher PCEs than those of the reference PPDT2FBT-A:PC61BO15 devices over all device-processable water/ethanol compositions. At the optimal water/ethanol composition (v/v = 15 : 85), the PCE of the PPDT2FBT-A:PC71BO15 eco-PSCs is 73% higher than that of the PC61BO15-based counterparts, as a result of enhanced light absorption. Importantly, the PC71BO15-based eco-PSCs show much higher tolerance in their PCEs to the water/ethanol composition. For example, the PCEs of the PPDT2FBT-A : PC71BO15 eco-PSCs at a 30 : 70 water/ethanol ratio maintain 89% of the optimal performance at a 15 : 85 ratio, whereas the PC61BO15-based devices only maintain 45%. This large difference in terms of water-tolerant behavior is mainly related to the different aggregation behaviors between PC71BO15 and PC61BO15 in blend films, which are carefully investigated using electrical, optical and morphological characterizations. This high water composition-tolerance affords an excellent reproducibility of the PC71BO15-based eco-PSCs with eco/human-friendly aqueous processing under ambient conditions.

Electron transport layers (ETLs) are critical for improving device performance and stability of perovskite solar cells (PVSCs). Herein, a distannylated electron-deficient bithiophene imide (BTI-Tin) is synthesized, which enables us to access structurally novel acceptor–acceptor (A–A) type polymers. Polymerizing BTI-Tin with dibrominated naphthalene diimide (NDI-Br) and perylene diimide (PDI-Br) affords two A–A copolymers P(BTI-NDI) and P(BTI-PDI). The all-acceptor backbone yields both low-lying highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels for the polymers, which combined with their high electron mobility render P(BTI-NDI) and P(BTI-PDI) as promising ETLs for perovskite solar cells (PVSCs). When applied as ETLs to replace the conventional [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) in planar p–i–n PVSCs, the PC61BM-free devices based on P(BTI-NDI) and P(BTI-PDI) achieve remarkable power conversion efficiencies (PCEs) of 19.5% and 20.8%, respectively, with negligible hysteresis. Such performance is attributed to efficient electron extraction and reduced charge recombination. Moreover, the devices based on P(BTI-NDI) and P(BTI-PDI) ETLs show improved stability compared to the PC61BM based ones due to the higher hydrophobicity of the new ETLs. This work provides important guidelines for designing n-type polymers to replace PC61BM as efficient ETLs for high-performance PVSCs with improved stability.