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Two kinds of polymer solar cells (PSCs) were fabricated with polymer donor PM6 and small molecule non‐fullerene acceptor L8‐BO as accepted based on bulk heterojunction (BHJ) or layer‐by‐layer (LbL) structure. The power conversion efficiency (PCE) of 18.43 % and 17.84 % can be achieved from the PSCs based on BHJ and LbL structure, respectively. Two kinds of PSCs exhibit the same open circuit voltage (VOC) of 0.88 V, which can be well explained from the same donor and acceptor materials and the same electrodes. The LbL based PSCs exhibit a relatively large short circuit current density (JSC) of 26.97 mA cm−2 and fill factor (FF) of 77.64 % in comparison with JSC of 26.64 mA cm−2 and FF of 76.07 % for BHJ based PSCs. The relatively high PCE of LbL based PSCs should be attributed to the sufficient exciton dissociation and charge collection efficiency, as well as the more balanced charge transport, which can be confirmed from the photogenerated current density dependence on the effective bias. This work demonstrates that layer‐by‐layer structure may have great potential in preparing highly efficient PSCs. [ABSTRACT FROM AUTHOR]

In this work, pseudo-bilayer planar heterojunction (PPHJ) all-polymer solar cells (APSCs) were constructed on the basis of the commonly used PY-IT and PM6 as the acceptor and donor, respectively. A nonfullerene small molecular acceptor (NF-SMA) BTP-eC9 was incorporated into the PY-IT layer as the solid additive in consideration of its similar building block to PY-IT. BTP-eC9 can serve as a photon capture reinforcer and morphology-regulating agent to realize more adequate photon capture, as well as a more orderly molecular arrangement for effective carrier transport. By incorporating 2 wt% BTP-eC9, the efficiency of PM6/PY-IT-based PPHJ-APSCs was boosted from 15.11% to 16.47%, accompanied by a synergistically enhanced short circuit current density (JSC, 23.36 vs. 24.08 mA cm−2) and fill factor (FF, 68.83% vs. 72.76%). In another all-polymer system, based on PBQx-TCl/PY-DT as the active layers, the efficiency could be boosted from 17.51% to 18.07%, enabled by the addition of 2 wt% L8-BO, which further verified the effectiveness of using an NF-SMA as a solid additive. This work demonstrates that incorporating an NF-SMA as a solid additive holds great potential for driving the development of PPHJ-APSCs. [ABSTRACT FROM AUTHOR]

The thin film deposition engineering of layer‐by‐layer (LbL) non‐fullerene organic solar cells (OSCs) favors vertical phase distributions of donor:acceptor (D:A), effectively boosting the power conversion efficiency (PCE). However, previous deposition strategies mainly aimed at optimizing the morphology of LbL films, and paid limited attention to the reproducibility of device performance. To achieve high device performance and maintain reproducibility, a strategy for hierarchical morphology manipulation in LbL OSCs is developed. A series of LbL devices are fabricated by introducing vacuum‐assisted molecular drift treatment (VMDT) to the donor or acceptor layer individually or simultaneously to elucidate the functionalities of this treatment. Essentially, the VMDT provides an extended drift driving force to manipulate the donor and acceptor molecules, resulting in a well‐defined vertical phase distribution and ordered molecular packing. These enhancements facilitate improvement in the D:A interface area and charge transport channel, ultimately contributing to impressive PCEs of 19.18% from 18.27% in the LbL devices. More importantly, using VMDT overcomes the notorious batch‐dependent and heat treatment degradation issues of OSCs, leading to excellent batch‐to‐batch reproducibility and enhanced stability of the devices. This reported method provides a promising strategy available for industrial and laboratory use to controllably manipulate the morphology of LbL OSCs. [ABSTRACT FROM AUTHOR]

Fullerene-derivatives based bulk heterojunctions hold an exceptionally important role on the roadmap of highly efficient organic solar cells (OSCs). In recent years, the utilization of the non-fused ring acceptors based OSCs has further improved photovoltaic power conversion efficiencies. Among these, one of the fundamental issues is to explore and to understand the spin-related polaron dissociation at charge transfer states because they act as the central unit for the photovoltaic action. It is also eagerly important to quantify some internal fields, such as hyperfine fields and the spin–orbit coupling. The aim of the work is to develop a method for unraveling the photoexcited spin states, particularly for the fullerene-derivative based OSC. Furthermore, it helps to elucidate a long-standing issue regarding the relatively high production of photocurrent for the P3HT:PC71BM system, which is indeed contrary to its counterpart the P3HT:PC61BM system. Their corresponding Jablonski diagrams have been determined in order to understand interior spin dynamics. The method of the study offers an alternative route for an understanding of device performance from the spin-related aspect. [ABSTRACT FROM AUTHOR]

Series of bulk heterojunction (BHJ) and layer‐by‐layer (LbL) all‐polymer solar cells (APSCs) were prepared with polymer PM6 as donor and polymer PY‐DT as acceptor based on conventional and inverted configuration. Benefiting from the sequential deposition strategy, the good vertical phase separation and more ordered molecular arrangement can be formed in the LbL APSCs. The conventional LbL APSCs exhibit an optimized power conversion efficiency (PCE) of 17.24% with a relatively large short circuit current density of 23.83 mA cm−2 and fill factor of 74.60%, photogenerated excitons near the indium tin oxide electrode can be efficiently utilized through energy transfer from PM6 to PY‐DT and the self‐absorption effect of PM6 for its long exciton diffuse distance. The 17.24% PCE of conventional LbL APSCs is higher than 16.72% of conventional BHJ APSCs, 14.59% of inverted BHJ APSCs and 12.41% of inverted LbL APSCs. The rather low PCE of 12.41% for the inverted LbL APSCs further indicates that the energy transfer from donor to acceptor and self‐absorption effect of donor should play a vital role in determining the performance of LbL APSCs. This work provides more insights on the exciton and carrier dynamic process in sequentially deposited active layer, providing more guidance for preparing efficient LbL APSCs. [ABSTRACT FROM AUTHOR]

Layer‐by‐layer all‐polymer solar cells (LbL all‐PSCs) are prepared with PM6 and PY‐IT by using sequential spin coating method. The exciton dissociation efficiency in acceptor layer near electrode is rather low due to the limited exciton diffuse distance and impossible energy transfer from narrow bandgap acceptor to wide bandgap donor. In this study, less PM6 is incorporated into PY‐IT layer to enhance exciton dissociation in PY‐IT layer near electrode. A power conversion efficiency (PCE) of 17.45% is achieved in the LbL all‐PSCs incorporating 10 wt% PM6 into PY‐IT layer, which is much larger than 16.04% PCE of PM6/PY‐IT‐based LbL all‐PSCs. Over 8% PCE enhancement can be realized by incorporating 10 wt% PM6 into PY‐IT layer, which is attributed to the enhanced exciton utilization efficiency in PY‐IT layers near electrode. The enhanced exciton utilization efficiency in PY‐IT layer can be confirmed from the quenched photoluminescence (PL) emission in PY‐IT:PM6 films. Meanwhile, charge transport in acceptor layers can be optimized by incorporating less PM6, as confirmed from the optimized molecular arrangement. This study indicates that the strategy of incorporating less donor into acceptor layer has great potential in fabricating efficient LbL all‐PSCs by improving exciton utilization efficiency in acceptor layer near electrode. [ABSTRACT FROM AUTHOR]

All polymer solar cells (APSCs) composed of polymeric donors and acceptors have attracted tremendous attention due to their unique merits of mechanical flexibility and good film formation property, which exhibit promising applications on wearable and flexible stretchable devices. Over 18% power conversion efficiency of APSCs has been achieved benefiting from the continuous development of functional layer materials innovation and device engineering evolution. In this review, the functional layer materials that enabled the recent progress of efficient APSCs are outlined, including typical polymer donors, emerging polymer acceptors based on polymerizing small molecule acceptors strategy, interfacial materials as well as the rational design rules for corresponding functional materials. From the perspective of device engineering evolution, the film deposition and treatment techniques are introduced, which play a vital role in manipulating film morphology through properly tuning the vertical component distribution and aggregation behavior of polymers. Meanwhile, the ternary strategy is also discussed as an effective method in promoting mechanical durability, stability, and thickness‐insensitive characteristics of APSCs facing for future applications. The challenges and outlooks on this filed are finally proposed for developing high‐performance APSCs. [ABSTRACT FROM AUTHOR]

The power conversion efficiencies (PCEs) of organic photovoltaics (OPVs) have reached more than 19%, along with the prosperous development of materials and device engineering. It is meaningful to make a comprehensive review of the research of OPVs for further performance improvement. In this review, some typical materials of high-performance OPVs are summarized, including representative polymer donor materials, non-fullerene acceptor materials, and interfacial modification materials, as well as their design rules for molecular engineering. From the point of view of device engineering, active layer treatment and deposition technology are introduced, which can play a critical role in adjusting the degree of molecular aggregation and vertical distribution. Meanwhile, a ternary strategy has been confirmed as an efficient method for improving the performance of OPVs, and the multiple roles of the appropriate third component in the photo-electronic conversion process are emphasized and analyzed. The challenges and perspectives concerning this region are also put forward for further developing high-performance OPVs. [ABSTRACT FROM AUTHOR]

The large energy loss (Eloss) is one of the main obstacles to further improve the photovoltaic performance of organic solar cells (OSCs), which is closely related to the charge transfer (CT) state. Herein, ternary donor alloy strategy is used to precisely tune the energy of CT state (ECT) and thus the Eloss for boosting the efficiency of OSCs. The elevated ECT in the ternary OSCs reduce the energy loss for charge generation (ΔECT), and promote the hybridization between localized excitation state and CT state to reduce the nonradiative energy loss (ΔEnonrad). Together with the optimal morphology, the ternary OSCs afford an impressive power conversion efficiency of 19.22% with a significantly improved open‐circuit voltage (Voc) of 0.910 V without sacrificing short‐cicuit density (Jsc) and fill factor (FF) in comparison to the binary ones. This contribution reveals that precisely tuning the ECT via donor alloy strategy is an efficient way to minimize Eloss and improve the photovoltaic performance of OSCs. [ABSTRACT FROM AUTHOR]

Interface modification is an important way to get better performance from organic solar cells (OSCs). A natural biomolecular material methionine was successfully applied as the electron transport layer (ETL) to the inverted OSCs in this work. A series of optical, morphological, and electrical characterizations of thin films and devices were used to analyze the surface modification effects of methionine on zinc oxide (ZnO). The analysis results show that the surface modification of ZnO with methionine can cause significantly reduced surface defects for ZnO, optimized surface morphology of ZnO, improved compatibility between ETL and the active layer, better-matched energy levels between ETL and the acceptor, reduced interface resistance, reduced charge recombination, and enhanced charge transport and collection. The power conversion efficiency (PCE) of OSCs based on PM6:BTP-ec9 was improved to 15.34% from 14.25% by modifying ZnO with methionine. This work shows the great application potential of natural biomolecule methionine in OSCs. [ABSTRACT FROM AUTHOR]

A series of binary and ternary polymer solar cells (PSCs) is successfully fabricated. The optimal ternary PSCs achieve a power conversion efficiency (PCE) of 18.14%, benefiting from the increased short circuit current density (JSC) of 26.53 mA cm−2 and fill factor (FF) of 78.51% in comparison with the JSCs (25.05 mA cm−2 and 25.65 mA cm−2) and the FFs (77.13% and 76.55%) of the corresponding binary PSCs. The photon harvesting ability of ternary active layers can be enhanced, which can be confirmed from the EQE spectral difference of the optimized ternary and binary PSCs, especially in the wavelength range from 680 nm to 800 nm. The refractive index and extinction coefficients of binary and ternary blend films are measured, which can well support the enhanced photon harvesting ability in different wavelength ranges. Photogenerated exciton distribution in active layers is simulated by the transmission matrix method based on the Beer–Lambert law. The photogenerated exciton density can be enhanced in the middle of the active layers by incorporating a third component in acceptors, which is conducive to charge collection by individual electrodes, resulting in the simultaneously enhanced JSC and FF of the optimal ternary PSCs. [ABSTRACT FROM AUTHOR]

Herein, asymmetric isomer effects are systematically explored by designing and synthesizing two benzo[c][1,2,5]thiadiazole (BT)‐fused nonacyclic electron acceptors. By changing from BP6T‐4F to asymmetric ABP6T‐4F, significantly enhanced dielectric constant and inhibited excessive molecular aggregation and unfavorable edge‐on orientation could be achieved. The reduced exciton binding energy also facilitates a more efficient dissociation process in PM6:ABP6T‐4F compared to PM6:BP6T‐4F with the same energy offset. Moreover, the weaker crystallization behavior enables a significantly enhanced miscibility between PM6 and ABP6T‐4F than that between PM6 and BP6T‐4F, which leads to an optimized micromorphology with smooth surface, suitable domain size, and ordered π–π stacking. Organic solar cells (OSCs) based on PM6:ABP6T‐4F achieve a 15.8% power conversion efficiency (PCE), which is remarkably higher than that of PM6:BP6T‐4F‐based OSCs (6.4%). Furthermore, ternary devices are also fabricated considering good compatibility between ABP6T‐4F and CH1007 to deliver a PCE over 17%. This study reveals the effectiveness and great potential of asymmetric isomerization strategy in regulating molecular properties, which will provide guidance for the future design of non‐fullerene acceptors. [ABSTRACT FROM AUTHOR]

In the field of non‐fullerene organic solar cells (OSCs), compared to the rapid development of non‐fullerene acceptors, the progress of high‐performance donor polymers is relatively slow. The property and performance of donor polymers in OSCs are often sensitive to the molecular weight of the polymers. In this study, a chlorinated donor polymer named D18‐Cl is reported, which can achieve high performance with a wide range of polymer molecular weight. The devices based on D18‐Cl show a higher open‐circuit voltage (VOC) due to the slightly deeper energy levels and an outstanding short‐circuit current density (JSC) owing to the appropriate long periods of blend films and less ([6,6]‐phenyl‐C71‐butyric acid methyl ester) (PC71BM) in mixed domains, leading to the higher efficiency of 17.97% than those of the D18‐based devices (17.21%). Meanwhile, D18‐Cl can achieve high efficiencies (17.30–17.97%) when its number‐averaged molecular weight (Mn) is ranged from 45 to 72 kDa. In contrast, the D18‐based devices only exhibit relatively high efficiencies in a narrow Mn range of ≈70 kDa. Such property and performance make D18‐Cl a promising donor polymer for scale‐up and low‐cost production. [ABSTRACT FROM AUTHOR]

To date, the power conversion efficiency (PCE) of lab‐scale organic solar cells (OSCs) has exceeded 17%, which heralds the bright future for commercial applications of OSCs. High‐performance OSCs with thick active layers are essential for large‐scale production. First, the relatively thick active layers should be more compatible with the roll‐to‐roll (R2R) large‐area processing, which is conducive to forming uniform and defect‐free active layers in the process of high‐speed, mass production. Second, the thick active layers can absorb more incident light in their spectral range, which helps thick‐film OSCs to obtain relatively high short‐circuit current density (JSC). So far, relatively little attention has been paid to thick‐film OSCs, and the PCE of thick‐film OSCs lags far behind its thin‐film analogues. Herein, the recent development of thick‐film OSCs is highlighted and the critical limit factors on the PCE of thick‐film OSCs are pointed out. Some strategies are highlighted to improve the efficiency of thick‐film OSCs. This review study will be helpful to the researchers engaging in the development of efficient thick‐film OSCs. [ABSTRACT FROM AUTHOR]

Ternary polymer solar cells (PSCs) have been widely demonstrated as an effective method to improve device performance. Meanwhile, the simple fabrication technology can be well kept with a single bulk heterojunction active layer, which is beneficial to the potential industrialization of PSCs. The photovoltaic parameters, such as short-circuit current density, open-circuit voltage, and fill factor, of ternary PSCs can be simultaneously improved by appropriately incorporating the third component, resulting in the increased power conversion efficiency (PCE) compared with the corresponding binary PSCs. To date, the PCE of ternary PSCs has exceeded 17% with the development of effective donors and non-fullerene acceptors. The fundamental designing rules of ternary PSCs are summarized to give some available guidelines for material selection. Next, the recent progress of efficient ternary PSCs based on various types is investigated. Then, some methods are introduced to investigate the working mechanisms of ternary PSCs. At length, the perspective toward the future development of ternary PSCs is discussed. [ABSTRACT FROM AUTHOR]

Thickness‐insensitive small molecule acceptors (SMAs) are still a great challenge for developing thick‐film organic solar cells (OSCs) towards practical use. Herein, two SMAs, MF1 and MF2, are designed and synthesized by employing a bifunctional end group with fluorine and methyl moieties. Combined with fused‐ring cores with alkyl side chains, both MF1 and MF2 exhibit ordered π–π stacking and high charge carrier mobilities in neat and blend films. The champion devices based on PM7:MF1 and PM7:MF2 deliver high power conversion efficiencies (PCEs) of 12.4% and 13.7%, and high fill factors (FFs) of 78.3% and 74.5%, respectively. With increasing active layer thickness, the FFs of the OSCs decrease relatively slowly, demonstrating the preferrable properties of MF1 and MF2 in terms of their thickness insensitivity, especially for MF1. As a result, the two thick‐film OSCs achieve over 11% PCEs at an active layer thickness over 400 nm (an FF close to 70% for PM7:MF1) and over 10% PCEs when the thickness is increased up to 500 nm. These are the highest PCEs among OSCs with such active layer thicknesses to date. This work reveals a molecular design strategy by reasonably combining fluorine and methyl together to simultaneously enhance charge carrier mobilities and fine‐tune the morphology, which is beneficial to achieve high‐performance thick‐film OSCs. [ABSTRACT FROM AUTHOR]

Abstract: Nonfullerene polymer solar cells (PSCs) are fabricated by using one wide bandgap donor PBDB‐T and one ultranarrow bandgap acceptor IEICO‐4F as the active layers. One medium bandgap donor PTB7‐Th is selected as the third component due to the similar highest occupied molecular orbital level compared to that of PBDB‐T and their complementary absorption spectra. The champion power conversion efficiency (PCE) of PSCs is increased from 10.25% to 11.62% via incorporating 20 wt% PTB7‐Th in donors, with enhanced short‐circuit current (JSC) of 24.14 mA cm−2 and fill factor (FF) of 65.03%. The 11.62% PCE should be the highest value for ternary nonfullerene PSCs. The main contribution of PTB7‐Th can be summarized as the improved photon harvesting and enhanced exciton utilization of PBDB‐T due to the efficient energy transfer from PBDB‐T to PTB7‐Th. Meanwhile, PTB7‐Th can also act as a regulator to adjust PBDB‐T molecular arrangement for optimizing charge transport, resulting in the enhanced FF of ternary PSCs. This experimental result may provide new insight for developing high‐performance ternary nonfullerene PSCs by selecting two well‐compatible donors with different bandgap and one ultranarrow bandgap acceptor. [ABSTRACT FROM AUTHOR]

Abstract: In this work, sidechain engineering on conjugated fused‐ring acceptors for conformation locking is demonstrated as an effective molecular design strategy for high‐performance nonfullerene organic solar cells (OSCs). A novel nonfullerene acceptor (ITC6‐IC) is designed and developed by introducing long alkyl chains into the terminal electron‐donating building blocks. ITC6‐IC has achieved definite conformation with a planar structure and better solubility in common organic solvents. The weak electron‐donating hexyl upshifts the lowest unoccupied molecular orbital level of ITC6‐IC, resulting in a higher VOC in comparison to the widely used ITIC. The OSCs based on PBDB‐T:ITC6‐IC reveal a promising power conversion efficiency of 11.61% and an expected high VOC of 0.97 V. The weaker π–π stacking induced by steric hindrance affords ITC6‐IC with enhanced compatibility with polymer donors. The blend film treated with suitable thermal annealing exhibits a fibril crystallization feature with a good bicontinuous network morphology. The results indicate that the molecular design approach of ITC6‐IC can be inspirational for future development of nonfullerene acceptors for high efficiency OSCs. [ABSTRACT FROM AUTHOR]

Side group of ITIC-like small molecular acceptor (SMA) plays a critical role in crystallization property. In this article, two new SMAs with n-hexylthienyl and n-hexylselenophenyl as side chain, namely ITCPTC-Th and ITCPTC-Se, are designed and synthesized by employing newly developed thiophene-fused ending group (CPTCN). And thiophene and selenophene side group substituted effects of SMA-based fullerene-free polymer solar cells (PSCs) are investigated. A stronger σ-inductive effect between selenophene side group and electron-donating backbone endows ITCPTC-Se with better optical absorption and higher LUMO level, ITCPTC-Th-based PSCs deliver a higher power conversion efficiency of 10.61%. Charge transport and collection, recombination loss mechanism, and morphology of blend films are intensively studied. These results confirm that side group substituted effects of SMAs are multiple and thiophene is a superior option to selenophene as aromatic side group of ITIC-like SMAs. [ABSTRACT FROM AUTHOR]

A series of polymer solar cells (PSCs) were fabricated with narrow band gap polymer poly{[4,9-dihydro-4,4,9,9-tetra(4-hexylbenzyl)-s-indaceno[1,2-b:5,6-b0]-dithiophene-2,7-diyl]-alt-[2,3-bis(3-(octyloxy)phenyl)-2,3-dihydro-quinoxaline-2,20-diyl] (PIDTDTQx), small molecule material 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl]squaraine (DIB-SQ), or their blend as electron donor, and [6,6]-phenyl-C71-butyric acid methyl ester (PC 71 BM) as electron acceptor. The champion power conversion efficiency (PCE) of ternary PSCs arrives to 6.49% with a short circuit current density ( J SC ) of 11.56 mA/cm 2 and a fill factor (FF) of 66% when the DIB-SQ doping ratio in donors is 9 wt%. The champion PCE values of binary PSCs with PIDTDTQx:PC 71 BM or DIB-SQ:PC 71 BM as the active layers are 5.47% or 1.78%, respectively. An apparent PCE improvement of 18.6% was obtained from the optimized ternary PSCs compared with binary PSCs with PIDTDTQx:PC 71 BM as the active layers. The underlying reason of PCE improvement was investigated from the absorption spectral complementary, photoluminescence emission quenching, intermolecular charge transfer, and the balance of charge carrier transport in ternary active layers. [ABSTRACT FROM AUTHOR]

A series of solution processed organic solar cells (OSCs) were fabricated with a two-dimensional conjugated small molecule SMPV1 as electron donor and fullerene derivatives PC 71 BM or ICBA as electron acceptor. The champion power conversion efficiency (PCE) of OSCs arrives to 7.05% for the cells with PC 71 BM as electron acceptor. A relatively large open circuit voltage ( V OC ) of 1.15 V is obtained from cells using ICBA as electron acceptor with an acceptable PCE of 2.54%. The fill factor (FF) of OSCs is 72% or 61% for the cells with PC 71 BM or ICBA as electron acceptor, which is relatively high value for small molecule OSCs. The relatively low performance of OSCs with ICBA as electron acceptor indicates that ICBA cannot play positive role in photoelectric conversion processes, which is very similar to the phenomenon observed from the OSCs with high efficient narrow band gap polymers other than P3HT as electron donor, the underlying reason is still in debate. The SMPV1 has strong self-assemble ability to form an ordered two dimensional lamellar structure, which provides an effective platform to investigate the effect of electron acceptor chemical structure on the performance of OSCs. Experimental results exhibit that ICBA molecules may prefer to vertical cross-intercalation among side chains of SMPV1, PC 71 BM molecules may have better miscibility with SMPV1 in the active layer. The different donor/acceptor (D/A) intermolecular arrangement strongly influences photon harvesting, exciton dissociation and charge carrier transport, which may provide a new sight on performance improvement of OSCs by adjusting D/A intermolecular arrangements. [ABSTRACT FROM AUTHOR]

Solvent additive 1,8-diiodooctane (DIO) is not almighty for improving the performance of polymer solar cells (PSCs). In this paper, the effect of solvent additive DIO and ethanol treatment on the performance of polymer solar cells (PSCs) with poly{[4,9-dihydro-4,4,9,9-tetra(4-hexylbenzyl)-s-indaceno[1,2-b:5,6-b′]-dithiophene-2,7-diyl]-alt-[2,3-bis(3-(octyloxy)phenyl)-2,3-dihydro-quinoxaline-2,2′-diyl] (PIDTDTQx) and [6,6]-phenyl-C71-butyric acid methyl ester (PC 71 BM) as the active layer was investigated. The power conversion efficiency (PCE) was decreased from 4.57% to 1.96% by adding 4 vol% DIO solvent additive for the active layer processed with 1,2-dichlorobenzene (DCB) as solvent. The negative effect of DIO on PCE from 1.94% to 1.18% of PSCs processed with chlorobenzene (CB) as solvent was further demonstrated. The PCE values of PSCs with DIO additive can be effectively increased from 1.96% to 3.71% for DCB as solvent and from 1.18% to 1.89% for CB as solvent by ethanol treatment on the active layer. The crystalline and morphology of active layers play the key role in determining the performance of PSCs. [ABSTRACT FROM AUTHOR]

A series of polymer solar cells (PSCs) based on poly (diketopyrrolopyrrole-terthiophene) (PDPP3T) and [6,6]-phenyl-C71-butyric acid methyl ester (PCBM) as active layer were fabricated to investigate the effect of 1,8-diiodooctane (DIO) on the performance of PSCs. The power conversion efficiency (PCE) of PSCs was increased from 3.77 % to 4.37 % for the cells with DIO additive. The underlying reason may be attributed to that DIO additive could make PCBM more dispersive in the active layer, forming a better bi-continuous interpenetrating network for excition dissociation and charge carrier transport. Therefore, the short circuit current density ( J) and fill factor (FF) was increased from 8.25 to 9.18 mA/cm and from 67.2 % to 70.0 % for the PSCs with DIO additive compared with PSCs without DIO additive. [ABSTRACT FROM AUTHOR]

Highlights: [•] The PCE of PSCs based on PBDTTT-C was increased to 5.35%, with 80% improvement by adding DIO. [•] The effect of DIO was investigated from the device physics researches. [•] The improvement of PCE is attributed to the improved hole transport and optical field strength in the active layer. [Copyright &y& Elsevier]

Abstract: A series of solution-processed small molecular solar cells (SMSCs) were fabricated with 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] (DIB-SQ) and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) as the active layer. The cells with MoO3 as anode interfacial layer and LiF as cathode interfacial layer have the maximum power conversion efficiency (PCE) 2.68%, with short circuit density (J sc ) of 8.2mA/cm2, open circuit voltage (V oc ) of 0.9V and fill factor (FF) of 36.3% under 100mW/cm2 illumination intensity. The key parameters, including J sc V oc , and FF of cells with MoO3 as anode interfacial layer and LiF as cathode interfacial layer, are improved about 54.7%, 26.9%, and 23.5% compared with these of cells using PEDOT:PSS as anode interfacial layer and LiF as cathode interfacial layer. The underlying reasons are mainly attributed to the effect of MoO3 layer on charge carrier collection and morphology of active layer. The effect of illumination intensity on the performance of cells was also discussed in detailed. [Copyright &y& Elsevier]

Abstract: The performance of polymer solar cells (PSCs), based on poly(3-hexylthiophene) (P3HT) and [6,6]phenyl-C71-butyric acid methyl ester (PC71BM), were improved by adding poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b:4,5-b′](dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl] (PBDTTT-C). The absorption region of the ternary blend films is extended into near infrared region (NIR). Power conversion efficiency (PCE) of the ternary blend PSCs is improved to 2.48% with 6% PBDTTT-C, which is 27% higher than the binary blend PSCs. The dominant mechanism for the PCE improvement could be attributed to the well balance between photon harvest and charge carrier transport by doping proper concentration PBDTTT-C. The energy transfer or charge carrier transfer directly between P3HT and PBDTTT-C was investigated, which are found to be positive for the performance improvement of ternary blend PSCs. [Copyright &y& Elsevier]

Abstract: Inverted polymer solar cells (IPSCs) were fabricated with cesium carbonate (Cs2CO3) modified indium tin oxide (ITO) substrates as the electrode and molybdenum trioxide (MoO3) modified Al as the anode. The Cs2CO3 dissolved in 2-ethoxyethanol was spin-coated on ITO substrates, showing snowflake-like morphology characterized by the scanning electron microscope (SEM). The absorption, X-ray diffraction as well as the morphology of the active layer were measured before and after annealing treatment. The IPSCs with annealing treatments on the active layers and MoO3 layers exhibited the maximum power conversion efficiency (PCE) approaching to 2%, with open circuit voltage (V oc ) of 0.57V, short circuit current density (J sc ) of 8.8mA/cm2 and fill factor (FF) of 38.7%. The performance of IPSCs was dramatically decreased by annealing treatment after the deposition of Al cathode, which may be due to the diffusion of Al atom crossing the MoO3 layer forming new channels for charge carrier collection. However, the new channels are not beneficial to the charge carrier collection, which is demonstrated from that the J sc of IPSCs was evidently decreased from 8.8 to 4.6mA/cm2 by annealing treatment after deposition Al layer. The annealing treatment after deposition of MoO3 could improve the interfacial contact to aid in electron extraction. [Copyright &y& Elsevier]

Abstract: Two series of P3HT-based polymer solar cell (PSCs) only with different electron acceptors PC70BM or PC60BM were investigated under the same conditions. The PSCs with PC70BM as the electron acceptor exhibit a relatively strong and broad absorption in the visible range and high external quantum efficiency, which results in a relatively high open circuit voltage (V oc ) of 0.62V, short circuit current density (J sc ) of 11.85mA/cm2 and power conversion efficiency (PCE) of 3.52%. The PSCs with PC60BM as the electron acceptor have a relatively low V oc of 0.58V, J sc of 10.68mA/cm2 and PCE of 3.02% due to the weak absorption of PC60BM in the visible light range. The function of PC70BM instead of PC60BM as electron acceptor could be summarized as follows: i) the strong absorption PC70BM in the visible range results in much more photon harvesting; ii) the relatively low electron mobility and relatively big size of PC70BM molecule influences the charge transporting and phase separation. The ultimate performances of PSCs are codetermined by the photon harvesting, exciton dissociation, charge carrier transport and collection. [Copyright &y& Elsevier]

Abstract: In poly(3-hexylthiophene) mixed with phenyl C61-butyric acid methyl ester heterojunction polymer solar cells, organic small molecular pentacene was introduced as the interfacial layer between PEDOT:PSS coated ITO substrates and polymer layer. It is found that the short circuit current density and power conversion efficiency were distinctly improved due to the introduction of the nanostructural pentacene interlayer. The nearly 100% power conversion efficiency improvement was obtained on the cells with a 4nm pentacene interlayer, which benefits from the increased short circuit current from 2.34mA/cm2 to 5.76mA/cm2. The morphology of different thicknesses of pentacene thin films was observed by atomic force microscopy. The effect of pentacene interlayer''s thickness on the distribution of light in the active layer was simulated by using a transfer matrix mode. [Copyright &y& Elsevier]

Abstract: A series of poly(3-hexylthiophene) (P3HT)/(6,6)-phenyl C60 butyric acid methyl ester (PCBM) bulk hetero-junction polymer solar cells were fabricated with different iodine (I2) doping concentrations. The short circuit current density (Jsc ) was increased to 8.7mA/cm2 from 4mA/cm2, meanwhile the open circuit voltage (Voc ) was decreased to 0.52V from 0.63V when the iodine doping concentration is 5%. The optimized power conversion efficiency of polymer solar cells (PSCs) with iodine doping is about 1.51%, which should be attributed to the better charge carrier transport and collection, and the more photon harvesting due to the red shift of absorption peaks and the widened absorption range to the longer wavelength. The morphology and phase separation of polymer thin films were measured by atomic force microscopy (AFM). The phase separation of P3HT and PCBM has been distinctly increased, which is beneficial to the exciton dissociation. The photocurrent density of PSCs with iodine doping was increased compared with the PSCs without iodine doping under the same effective voltage. [Copyright &y& Elsevier]

Abstract: Recent years, the power conversion efficiency (PCE) of normal configuration organic solar cells (OSCs) has obtained rapid progress to reach more than 6% under standard illumination, which is reasonable value for the commercial criterion. More and more research attention has been paid on the stability and lifetime of OSCs. A novel structural OSCs with high work function metal or metal oxide as the top electrode and low work function metal as the bottom anode is proposed and named as inverted configuration OSCs. The inverted configuration OSCs with high work function metal as top cathode could improve OSCs''s lifetime, i.e., protecting cells from the damage by oxygen and moisture in air. Furthermore, the inverted configuration OSCs is the appealing alternative to the conventional regular structure due to the inherent vertical phase separation in the polymer active layers and high stability or long device lifetime. The inverted configuration OSCs have not only achieved an impressive PCE of 4.4%, but also exhibited an exceptional device lifetime without encapsulation. In this review article, the recent developments and vital researches on the inverted configuration OSCs are summarized. [Copyright &y& Elsevier]

Ternary polymer solar cells (PSCs) are designed by incorporating varied PC71BM into a PBDB‐T:INPIC‐Si‐based binary system. The PC71BM incorporation can replenish weak absorption of PBDB‐T and INPIC‐Si in the short wavelength from 300 to 500 nm. Effective charge transport channels can be formed in ternary active layers due to good compatibility of the used materials. The optimized ternary PSCs exhibit a power conversion efficiency (PCE) of 13.26% with short‐circuit current density (JSC) of 20.98 mA cm−2, open‐circuit voltage of 0.892 V, and fill factor (FF) of 70.84%. The 13.26% PCE is among the top values for ternary PSCs with fullerene derivative and nonfullerene materials as acceptors. An approximately 12.5% PCE improvement is obtained compared with INPIC‐Si‐based binary PSCs, originating from simultaneously increased JSC and FF of the optimized ternary PSCs. The balanced photon harvesting is obtained in the whole wavelength range by regulating PC71BM content in acceptors, leading to increased JSC of ternary PSCs. The molecular arrangement and phase separation are well optimized in ternary blend films, resulting in the enhanced FF of ternary PSCs. The photogenerated exciton distribution is optimized according to optical field distribution of ternary active layers, which further support the JSC and FF improvement. [ABSTRACT FROM AUTHOR]

Small molecule acceptors (SMAs) for polymer solar cells (PSCs) have become a hot topic due to the resulting breakthrough of power conversion efficiency (PCE). To investigate the effect of extending central ladder‐type conjugated cores on the performance of PSCs, hexacyclic‐, heptacyclic‐, and octacyclic‐fused‐ring‐based SMAs (T6Me, T7Me, and T8Me) are designed and synthesized, structured with the same 2‐(1‐methyl‐6‐oxo‐5,6‐dihydro‐4H‐cyclopenta[c]thiophen‐4‐ylidene)malononitrile (CPTCN‐M) termini. The extension of backbone conjugation leads to the red shift of the absorption spectra, and elevates both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Pairing with polymer donor PM6, T6Me‐based PSC displays a higher PCE of 12.09% than T7Me‐ (PCE of 8.96%) and T8Me‐based PSCs (PCE of 6.09%). This trend is ascribed to the lower bimolecular recombination, more favorable morphology features as well as more balanced hole and electron mobilities in the PM6:T6Me blend. Moreover, the low optical gap of T6Me and relatively high open‐circuit voltage (VOC) for the PM6:T6Me blend film results in low energy loss (Eloss) of 0.51 eV. [ABSTRACT FROM AUTHOR]

Efficient ternary polymer solar cells (PSCs) are prepared with poly‐[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′] dithiophene‐co‐3fluorothieno[3,4‐b]thiophene‐2‐carboxylate] (PTB7‐Th):COi8DFIC as host system and medium bandgap material BDTThIT‐4F as the third component. The power conversion efficiency of PSCs can be increased from 11.47% to 13.08% by incorporating 20 wt% BDTThIT‐4F in acceptors, along with the simultaneously improved three key photovoltaic parameters. The absorption edge of ternary blend films can be tilted up in long wavelength range by incorporating appropriate BDTThIT‐4F, although the bandgap of BDTThIT‐4F is wider than that of COi8DFIC, leading to the extended external quantum efficiency spectra of ternary PSCs. The tilted up absorption edge of blend films should be attributed to the variation of COi8DFIC molecular arrangement, which can be well demonstrated from the transient and steady absorption spectra of blend films with different donors and acceptors. A new ground state bleach signal can be clearly observed in transient absorption spectra of the optimized ternary blend films, which may be due to the varied COi8DFIC molecular energy levels by incorporating BDTThIT‐4F. Meanwhile, the lifetimes on excited states are increased in the ternary blend films, which is beneficial to exciton dissociation for improving the performance of ternary PSCs. Efficient ternary non‐fullerene polymer solar cells (PSCs) are fabricated with poly‐[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′] dithiophene‐co‐3‐fluorothieno[3,4‐b]thiophene‐2‐carboxylate] (PTB7‐Th):COi8DFIC:BDTThIT‐4F as active layers. The power conversion efficiency is increased from 11.47% to 13.08% by incorporating 20 wt% BDTThIT‐4F in acceptors, which is attributed to the tilted up absorption edge and the optimized phase separation of ternary active layers. [ABSTRACT FROM AUTHOR]

Abstract Polymer solar cells (PSCs) were fabricated with PTB7-Th as donor and fluorinated non-fullerene materials IEICO-4F, IT-4F or their mixture as acceptor. Binary PSCs with IEICO-4F or IT-4F as acceptor exhibit a power conversion efficiency (PCE) of 10.74% or 8.81% and fill factor (FF) of 63.32% or 73.90%, respectively. The PCE of 11.78% is achieved for the optimized ternary PSCs with 25 wt% IT-4F in acceptors, resulting from over 12.3% FF improvement (71.12% vs 63.32%). The distinguished FF improvement should be attributed to the optimized molecular arrangement and phase separation scale by incorporating the third component as morphology regulator. This work provides an efficient strategy on selecting materials for achieving efficient ternary PSCs by combining the superior photovoltaic parameters of two corresponding binary PSCs, in addition to the used materials with complementary absorption spectra. Graphical abstract Over 12.3% fill factor is improved by incorporating 25 wt% IT-4F in acceptor as morphology regulator. The champion PCE of 11.78% is achieved for the optimized ternary PSCs by combining the superior photovoltaic parameters of two corresponding binary PSCs. Image 1 Highlights • The PCE of the optimized ternary PSCs arrives to 11.78%. • Over 12.3% FF improvement is obtained and analyzed. • A smart ternary strategy is proposed. [ABSTRACT FROM AUTHOR]

• The LbL APSCs exhibit a PCE of 18.55%, which should be among the highest values for LbL APSC with eco-friendly solvent. • The exciton dissociation in ternary LbL APSCs can be promoted by the formation of alloyed state. • The smaller energy loss of optimized LbL APSCs is conductive to the improvement of V OC. In this work, a series of eco-friendly solvent-processed all-polymer solar cells (APSCs) were fabricated by employing the sequentially spin-coating method. Two polymer donor materials PBQx-TCl and PM6 were deliberately selected due to their similar chemical structure, preferring to form the alloyed state for better exciton dissociation and hole transport in the layer-by-layer (LbL) APSCs. The better exciton dissociation between PBQx-TCl and PM6 can be confirmed from PL spectra of neat and blend films, as well as the short-circuit current densities (J SC) of special cells without acceptor layer. The optimized ternary LbL APSCs with 30 wt% PM6 in donor layer exhibit the power conversion efficiency (PCE) of 18.55 %, originating from the simultaneously improved J SC of 25.16 mA cm−2, open-circuit voltage (V OC) of 0.966 V, and fill factor of 76.33 %. The increased V OC of ternary LbL APSCs is mainly attributed to the decreased energy loss due to the good compatibility of the two polymer donors. The PCE of 18.55 % should be among the highest value for LbL APSCs processed by eco-friendly solvent. [ABSTRACT FROM AUTHOR]

• Raman mapping images provide intuitive evidences on good compatibility of MF1 and Y6. • MF1 and Y6 prefer to form alloy-like state in ternary active layers. • The optimized ternary PSCs achieve a PCE of 17.22% and a certified PCE of 16.8%. Ternary strategy has been considered as an efficient method to achieve high performance polymer solar cells (PSCs). A power conversion efficiency (PCE) of 17.22% is achieved in the optimized ternary PSCs with 10 wt% MF1 in acceptors. The over 8% PCE improvement by employing ternary strategy is attributed to the simultaneously increased J SC of 25.68 mA cm−2, V OC of 0.853 V and FF of 78.61% compared with Y6 based binary PSCs. The good compatibility of MF1 and Y6 can be confirmed from Raman mapping, contact angle, cyclic voltammetry and morphology, which is the prerequisite to form alloy-like state. Electron mobility in ternary active layers strongly depends on MF1 content in acceptors due to the different lowest unoccupied molecular orbital (LUMO) levels of Y6 and MF1, which can well explain the wave-like varied FF of ternary PSCs. The third-party certified PCE of 16.8% should be one of the highest values for single bulk heterojunction PSCs. This work provides sufficient references for selecting materials to achieve efficient ternary PSCs. [ABSTRACT FROM AUTHOR]

The PCE of 15.83% is achieved for the optimized opaque PSCs with PM6:Y6 as active layer of 100 nm, resulting from the well-balanced photon harvesting and charge collection. The PCE and AVT of semitransparent PSCs can be simultaneously optimized by adjusting the thickness of Ag layer. The PCE of 12.37% and AVT of 18.6% are achieved for semitransparent PSCs with 10 nm thick Ag and 1 nm thick Au layers as electrode. A series of opaque and semitransparent polymer solar cells (PSCs) were fabricated with PM6:Y6 as active layers, and 100 nm Al or 1 nm Au/(20, 15, 10 nm) Ag layer as electrode, respectively. The power conversion efficiency (PCE) of opaque PSCs arrives to 15.83% based on the optimized active layer with a thickness of 100 nm, resulting from the well-balanced photon harvesting and charge collection. Meanwhile, the 100 nm PM6:Y6 blend film exhibits a 50.5% average visible transmittance (AVT), which has great potential in preparing efficient semitransparent PSCs. The semitransparent electrodes were fabricated with 1 nm Au and different thick Ag layers, exhibiting a relatively high transmittance in visible light range and relatively low transmittance in near infrared range. The PCE and AVT of the semitransparent PSCs can be adjusted from 14.20% to 12.37% and from 8.9% to 18.6% along with Ag layer thickness decreasing from 20 to 10 nm, respectively, which are impressive values among the reported semitransparent PSCs. [ABSTRACT FROM AUTHOR]

A PCE of 19.13% is achieved in ternary SS-PSCs with two well-compatible polymer donors (PM1 and D18) and an efficient non-fullerene acceptor (L8-BO), resulting from all-around enhanced J SC , V OC and FF. The optimized vertical phase separation, enhanced charge transport and collection should be the critical factors for PCE improvement of ternary SS-PSCs. [Display omitted] • The optimized ternary SS-PSCs achieved higher PCE of 19.13% than binary SS-PSCs. • Two polymers PM1 and D18 with similar chemical structures were selected as donors. • Energy transfer from D18 to PM1 provides an additional exciton utilization channel. Series of sequentially spin-coated polymer solar cells (SS-PSCs) are fabricated with donor layers containing PM1, D18 or PM1:D18 and sequentially spin-coated L8-BO acceptor layer. Photon harvesting of donor layers could be enhanced by optimizing the weight ratios of PM1 to D18 due to their distinct optical band-gap. The optimized ternary SS-PSCs exhibit a power conversion efficiency of 19.13%, resulting from the simultaneously enhanced short-circuit-current density (J SC) of 27.20 mA/cm2, open-circuit voltage (V OC) of 0.90 V and fill factor of 78.53% in comparison to those of PM1/L8-BO based SS-PSCs. The increased J SC s of ternary SS-PSCs is due to the enhanced photon harvesting and efficient exciton utilization assisted by an additional channel from D18 to PM1 through energy transfer. The increased V OC of optimal ternary SS-PSCs benefits from the little larger V OC of binary SS-PSCs with D18 as donor layer. The donor/acceptor interfacial energy is slightly increased by incorporating D18 in donor layer, which is conducive to form the optimized vertical phase separation to decrease charge recombination loss. This work indicates that ternary strategy is also a versatile and effective method in improving the performance of SS-PSCs. [ABSTRACT FROM AUTHOR]

Two isomeric small molecules based on perylene diimide with 4,4′-/2,4′-substituted spirobifluorene as the core were designed and synthesized as acceptor materials for organic solar cells. According to density functional theory calculations, the different sites of the substitution, either the 4-position or the 2-position of the spirobifluorene led to significant distinction in both molecular structure and electronic distribution. The dihedral angles between the two perylene diimide units were calculated as well, indicating the 2-position linkage molecule had a more isotropic spatial arrangement. X-ray diffraction results showed the more ordered molecular packing of the 2-position linked molecule. In consequence, when blended with a donor, these two acceptors exhibited different device performance, especially the short circuit currents. The solar cell based on the 2-position linkage molecule achieved the best power conversition efficiency of 4.56% with 2% 1-chloronaphthalene as an additive. The hole and electron mobilities were also improved greatly after adding 2% 1-chloronaphthalene, which benefited the short circuit currents. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 17.98% PCE is achieved by combining LbL processing method and ternary strategy. • The alloyed state is formed to achieve slightly increased V OC of ternary LbL PSCs. • MAZ-2 can induce increased D/A interfacial energy for more ideal vertical phase separation. In this work, ternary layer-by-layer (LbL) polymer solar cells (PSCs) were prepared with D18-Cl/Y6 as host system and MAZ-2 as the second acceptor. The open circuit voltage (V OC) of LbL PSCs can be increased with the addition of MAZ-2, signifying the alloy state formation between Y6 and MAZ-2 with good compatibility. A power conversion efficiency (PCE) of 17.98% can be achieved in the optimal ternary LbL PSCs with acceptor layer prepared from Y6:MAZ-2 (10:1, wt/wt) blend solution, accompanying with synchronously improved short circuit current density (J SC) of 27.10 mA cm−2, open circuit voltage (V OC) of 0.88 V and FF of 75.39% as compared to those of host binary system. The J SC improvement of ternary LbL PSCs should be closely related to more efficient exciton utilization through the additional channel of intermolecular energy transfer from MAZ-2 to Y6. The interfacial energy between donor and acceptor layer can be increased by adding MAZ-2 with lower compatibility with D18-Cl, which may lead to the weakened interpenetration of acceptor into donor layer to form more ideal vertical phase separation for efficient charge transport and collection. This work provides a guidance to select the third component having appropriate compatibility with host materials for realizing performance improvement of LbL PSCs. [ABSTRACT FROM AUTHOR]

The conventional LbL APSCs exhibit an optimal PCE of 15.28% with polymer PM6 as donor and polymer PYF- T -o as acceptor, which is higher than 14.97%, 13.03% and 8.54% obtained from the conventional BHJ APSCs, inverted BHJ APSCs and inverted LbL APSCs, benefiting from the higher exciton ultilization efficiency in conventional LbL active layers. [Display omitted] • Conventional LbL APSCs exhibit higher PCE of 15.28% than conventional BHJ APSCs. • Efficient energy transfer provides an additional exciton utilization channel in conventional LbL APSCs. • LbL structure has great potential in achieving highly efficient APSCs. Series of conventional and inverted all-polymer solar cells (APSCs) were prepared with polymer PM6 as donor and polymer PYF- T -o as acceptor based on layer-by-layer (LbL) or bulk heterojunction (BHJ) structure. The power conversion efficiency (PCE) of 15.28% and 14.97% can be achieved in conventional LbL and BHJ APSCs, respectively. The relatively high PCE of conventional LbL APSCs is mainly originated from short circuit current density (J SC) improvement caused by optimized phase separation and more ordered molecular arrangement for efficient charge extraction and transport in layered active layers. Meanwhile, the efficient energy transfer from PM6 to PYF- T -o should provide an additional exciton utilization channel, which is also responsible for relatively high performance in conventional LbL APSCs. It is worth noting that the inverted APSCs exhibit low PCE as compared to that of corresponding conventional APSCs, especially for the inverted LbL APSCs with only 8.54% PCE. The markedly inferior PCE in inverted LbL APSCs is mainly attributed to the insufficient PYF- T -o exciton dissociation, which can be demonstrated from the greatly low EQE spectra in long wavelength region as compared to that of other type APSCs. This work provides more deep insight on the dynamic process in LbL active layers, which should contribute to the construction of highly efficient APSCs based on LbL processing method. [ABSTRACT FROM AUTHOR]

Interfacial modification is one of the key ways to improve the performance of inverted organic solar cells (IOSCs). In this work, the performance of IOSCs with PM6:Y6 as the active layer is effectively improved by introducing the green natural biomaterial histidine to modify ITO or zinc oxide (ZnO). With the modification of histidine, ITO and ITO/ZnO films have smoother surfaces, better compatibility with the active layer, and better energy level match with the acceptor, which are beneficial to promote charge transfer and inhibit charge recombination for the IOSCs with histidine or ZnO/histidine as electron transport layers (ETLs). The power conversion efficiency (PCE) of IOSCs with histidine and ZnO/histidine as ETLs are improved to 12.10% and 16.02% along with the simultaneous increase of short circuit current density (J SC), open circuit voltage (V OC), and fill factor (FF). Meanwhile, the IOSCs with histidine or ZnO/histidine as ETLs have better stability compared to the IOSCs with ZnO as ETLs. This study suggests that natural biomaterial histidine as an ETL has capacity to improve the efficiency of IOSC by effective modification to ITO or ITO/ZnO. [Display omitted] • The histidine is biomaterial, which can be extracted from plants and animals. • The histidine as an ETL is successfully introduced into the IOSCs to modify ZnO. • Interfacial properties between ZnO and active layer is better after adding histidine. • The introduction of histidine are beneficial to promote charge transfer in IOSCs. [ABSTRACT FROM AUTHOR]

Abstract: This review summarizes the optical and electrical models of bulk heterojunction (BHJ) polymer solar cells (PSCs) and numerically simulates and analyzes the performance of the PSCs. A complete simulation of a conventional BHJ device based on the polymer P3HT is presented and results are compared with the experimental data. Key factors affecting the device performance, including the photo absorption, quantum efficiency, short-circuit current, fill factor, and open-circuit voltage of the device, are analyzed and summarized. Simulations on inverted, semitransparent, and large-area PSCs are performed and findings are compared with experimental results. Simulations reveal the effects of optical spacer layers, different thicknesses, carrier mobilities, light intensities, contact barriers, effective bandgaps, recombination coefficients, and energy-level bending on the quantum efficiency, short-circuit current, fill factor, and open-circuit voltage of the PSCs. Differences between conventional and inverted geometry, opacity and semitransparency, and small and large-area PSCs are discussed based on the simulations. A power conversion efficiency of 11.0% is predicted for the PSC based on P3HT. Results suggest the need to further reduce the series resistance in large-area PSCs. [Copyright &y& Elsevier]

[Display omitted] • The PM6Ir1:Y6 based PSCs give a PCE improvement of about 7%. • The population and lifetime of the triplet excitons are increased. • The photon harvesting, bulk and surface morphologies are optimized. With the sharp growth of non-fullerene acceptors, it is still challenging to develop new polymer donors for highly efficient polymer solar cells (PSCs). Here, a series of metallated terpolymer donors PM6Irx (x = 1%, 3%, 5%) are synthesized by incorporating a new iridium complex, named M1, into the backbone of the state-of-the-art polymer PM6. The M1 shows a strong absorption in the visible region, which is beneficial to enhance photon harvesting in the active layer. The PM6Ir1:Y6 based PSCs exhibit the best power conversion efficiency (PCE) of 16.71% with short-circuit current density (J SC) of 26.16 mA cm−2, open-circuit voltage (V OC) of 0.848 V and fill factor (FF) of 75.33%. A PCE improvement of about 7% is achieved compared with PM6Ir0:Y6 based control device with PCE of 15.65%, which is due to the markedly increased J SC and FF. The introduction of a moderate amount of M1 enhances the photon harvesting, triplet excitons and lifetime, charge mobility as well as optimizes the active layer morphology. This work indicates that iridium complexes with strong absorption in the visible region have a great potential to promote the photovoltaic performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 17.71% PCE is achieved in ternary OSCs with 100 nm thick active layer. • The ternary OSCs have good thickness-tolerance, benefiting for mass production. • Providing new viewpoint for understanding performance improvement of OSCs. Ternary-blend organic solar cells (TOSCs) are fabricated with PM6:BTP-4F-12 as the host system and IT-M as the third component. The third component IT-M takes multiple roles in improving performance of TOSCs through reducing energy-loss of the optimized TOSCs, optimizing molecular arrangement and phase separation in active-layers. The well optimized molecular arrangement and phase separation can be beneficial to charge separation and transport in TOSC, which can be confirmed by the characterization of 2D grazing incidence wide-angle X-ray scattering, transmission electron microscopy, magneto-photocurrent, as well as electrochemical impedance spectroscopy. By finely optimizing IT-M content, a power-conversion-efficiency (PCE) of 17.71% is achieved in the optimized TOSCs, benefiting from simultaneously enhanced short-circuit-current density (J SC) of 25.95 mA cm−2, open-circuit-voltage (V OC) of 0.875 V and fill-factor (FF) of 78.02% in comparison with the OSCs with PM6:BTP-4F-12 as active-layers. Furthermore, average PCE over 15% can be achieved from twenty individual TOSCs with active-layer thickness of 300 nm, indicating the optimized TOSCs have excellent thickness tolerance. [ABSTRACT FROM AUTHOR]

Abstract: The critical review on the recent development of novel narrow bandgap polymers for high-efficiency polymer solar cells concentrates on (i) the structural design of narrow bandgap polymers, which occupy a central place in recent advances in high-efficiency polymer solar cells, (ii) the intrinsic physics and chemistry of special properties, such as absorption, bandgap and energy levels, and (iii) the correlation of polymer structure and device fabrication with their photovoltaic performances. The statistical summaries of their device parameters are also discussed. The description of these structure–property correlations may guide the rational design of polymer structures and the reasonable evaluation of their photovoltaic performance. [Copyright &y& Elsevier]

Abstract: Organic solar cells (OSCs) have emerged as a cost-effective solution in fabricating large-area, lightweight and flexible devices by using simple techniques with low environmental impact. With the power conversion efficiency of polymeric bulk-heterojunction (BHJ) OSCs reaching ∼6%, pushing OSCs further to practical applications has now motivated intensified research interests in designing new material and implementing new device architecture. Conjugated oligomers have shown specific advantages in synthesis, purification and structure definition compared with polymers. Recent years have witnessed intensive research in developing high-efficiency BHJ cells with conjugated oligomers as either electron-donating materials or accepting materials. This account primarily focuses on the recent development of conjugated oligomers and their application in BHJ solar cells. The results show that these oligomeric donors or acceptors are promising to construct high efficiency BHJ solar cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A naphthalene-fused octacyclic electron-donating central core was constructed for non-fullerene acceptors. • Favorable morphologies and transport pathway were achieved when blended with PM6. • A high PCE of 12.3% with FF of 72.38% were obtained for organic solar cells. To develop new central core structure, we designed and synthesized a naphthalene-fused octacyclic electron-rich block, named as NITT. With the NITT ladder-type core and two distinct terminal groups (IC-2F and CPTCN-Cl), two novel A-D-A-type non-fullerene acceptors (NFAs), namely NITT-BF and NITT-ThCl , were constructed. Two NFAs exhibit broad and intense absorption and high electron mobility due to the coplanar architecture. When blended with polymer donor PM6, NITT-BF -based device acquires more favorable morphology, higher exciton dissociation and charge collection efficiency, and higher and more balanced hole/electron mobilities, resulting in the significantly improved short-circuit current density (J SC) of 18.08 mA cm−2 and fill factor (FF) of 72.38%. Additionally, both NITT-BF - and NITT-ThCl -based devices deliver very high open-circuit voltages (V OC s) (0.94 V for NITT-BF -based device and 0.97 V for NITT-ThCl -based device). Therefore, PM6: NITT-BF -based device yields an optimal PCE of up to 12.30%, which is much higher than that of PM6: NITT-ThCl -based device (9.58%). Notably, the high PCE of 12.30% is one of the best values for naphthalene-fused NFAs in organic solar cells (OSCs). These results indicate that the linear ladder-type NITT is a promising electron-donating core for constructing high-performance NFAs and terminal strategy is a good way to further boost the photovoltaic performance of OSCs. [ABSTRACT FROM AUTHOR]

Recently, A-DA′D-A-type small molecular acceptors (SMAs) with benzo [ c ][1,2,5]thiadiazole (BT)-fused central cores have shown tremendous progress in organic solar cells (OSCs). In this work, two new BT-fused pentacyclic core based SMAs, namely BTT-4F and BTTCN-Cl, were designed and synthesized. Compared to BTT-4F, BTTCN-Cl not only delivers a reduced bandgap but an elevated lowest unoccupied molecular orbital (LUMO) energy level, which leads to a higher open-circuit voltage (V OC) and thus a lower energy loss in PM6:BTTCN-Cl-based device. However, PM6:BTT-4F-based OSCs achieves a significantly higher power conversion efficiency (PCE) (10.03%) than that of BTTCN-Cl-based OSCs (6.56%) due to its higher short-circuit density (J SC) and fill factor (FF). More favorable morphology accompanying with higher and more balanced hole/electron mobilities was obtained in PM6:BTT-4F active layer, which well accounts for the high PCE in BTT-4F-based OSCs. • Two novel SMAs based on fused pentacyclic benzo [ c ] [1,2,5]thiadiazole core were synthesized and developed. • The two SMAs exhibit intense light absorption in the range of 600–800 nm. • A high V OC of 0.90 V was obtained. • A high PCE of 10.03% was achieved in organic solar cells. [ABSTRACT FROM AUTHOR]