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Fluorination strategy is demonstrated to be a successful approach for optimizing the electron distribution and morphology of organic photovoltaic materials. The previous works focus on introducing only a few C(sp2)─F bonds into conjugated backbone or C(sp3)─F bonds into sidechains. Herein, a new strategy by introducing C(sp3)─F polyfluoride unit into the backbone is proposed, wherein the fluorine atoms are not involved into the conjugation but can promote the intermolecular interaction between backbones. Two wide‐bandgap fluoropolymers are prepared and employed as the third component for ternary organic solar cells. As expected, even if there are six fluorine atoms in a single repeat unit, the relevant fluoropolymers possess complementary absorption and aligned energy levels. More importantly, the polyfluoride backbone affords adequate non‐covalent interactions, consequently enhancing the polymer aggregation and packing order, which is verified by a fibril‐like morphology in the blend film with the host polymer PM6 and only 10 wt.% fluoropolymer. In addition, the decreased surface energy caused by polyfluoride unit is beneficial for the improvement of domain purity and the formation of nanoscale phase separation between donor and acceptor materials. As a result, the fluoropolymer‐assisted ternary device displays a higher efficiency of 18.74% compared with the binary device (17.39%). [ABSTRACT FROM AUTHOR]

The development of high‐efficiency organic solar cells (OSCs) processed from non‐halogenated solvents is crucially important for their scale‐up industry production. However, owing to the difficulty of regulating molecular aggregation, there is a huge efficiency gap between non‐halogenated and halogenated solvent processed OSCs. Herein, we fabricate o‐xylene processed OSCs with approaching 20 % efficiency by incorporating a trimeric guest acceptor named Tri‐V into the PM6:L8‐BO‐X host blend. The incorporation of Tri‐V effectively restricts the excessive aggregation of L8‐BO‐X, regulates the molecular packing and optimizes the phase‐separation morphology, which leads to mitigated trap density states, reduced energy loss and suppressed charge recombination. Consequently, the PM6:L8‐BO‐X:Tri‐V‐based device achieves an efficiency of 19.82 %, representing the highest efficiency for non‐halogenated solvent‐processed OSCs reported to date. Noticeably, with the addition of Tri‐V, the ternary device shows an improved photostability than binary PM6:L8‐BO‐X‐based device, and maintains 80 % of the initial efficiency after continuous illumination for 1380 h. This work provides a feasible approach for fabricating high‐efficiency, stable, eco‐friendly OSCs, and sheds new light on the large‐scale industrial production of OSCs. [ABSTRACT FROM AUTHOR]

The side‐chain has a significant influence on the optical properties and aggregation behaviors of the organic small molecule acceptors, which becomes an important strategy to optimize the photovoltaic performance of organic solar cells. In this work, we designed and synthesized three brand‐new nonfused ring electron acceptors (NFREAs) OC4‐4Cl‐Ph, OC4‐4Cl‐Th, and OC4‐4Cl‐C8 with hexylbenzene, hexylthiophene, and octyl side chains on the π‐bridge units. Compared with OC4‐4Cl‐Ph and OC4‐4Cl‐Th, OC4‐4Cl‐C8 with linear alkyl side chain has more red‐shift absorption, which is conducive to obtaining higher short‐circuit current density. Additionally, the OC4‐4Cl‐C8 film exhibits a longer exciton diffusion distance, and the D18:OC4‐4Cl‐C8 blend film displays faster hole transfer, weaker bimolecular recombination, and more efficient exciton transport. Furthermore, The D18:OC4‐4Cl‐C8 blend films may effectively form interpenetrating networks that resemble nanofibrils, which can facilitate exciton dissociation and charge transport. Finally, OC4‐4Cl‐C8‐based devices can be created a marvellously power conversion efficiency (PCE) of 16.56%, which is much higher than OC4‐4Cl‐Ph (12.29%)‐ and OC4‐4Cl‐Th‐based (11.00%) ones, being the highest PCE among the NFREA based binary devices. All in all, we have validated that side‐chain engineering is an efficient way to achieve high‐performance NFREAs. [ABSTRACT FROM AUTHOR]

Nowadays, it is still a great challenge to obtain high‐performance green‐solvent‐processed organic solar cells (OSCs). In this study, a ternary blend strategy (one donor and two acceptors, 1D/2A) is developed to solve the difficulty of film morphology modulation during the fabrication of high‐performance green‐solvent‐processed OSCs. A typical high‐performance halogenated‐solvent processable binary system D18:BTP‐eC9‐4F is selected as the host, its green‐solvents‐processed devices show an inferior power conversion efficiency (PCE) of ≈16%. SM16 with two 3D shape persistent end groups is selected as the third component due to its high fluorescence quantum yield, reduced intermolecular interaction, good solubility, and moderate crystallinity. As a result, the ternary devices display bicontinuous interpenetrating networks, reduced energy loss, and suppressed charge carrier recombination losses. Hence, an excellent PCE of 18.20% is achieved for the D18:BTP‐eC9‐4F:SM16 ternary devices, which is much higher than D18:BTP‐eC9‐4F‐based binary ones and also one of the highest PCEs for the green‐solvents‐processed OSCs. Besides, this strategy also demonstrates a good universality for other binary systems and becomes an effective pathway for the development of green‐solvent processable high‐performance OSCs. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: By simplifying the π‐bridge unit, a nonfused ring electron acceptor (NFREA) BM‐2F was designed and synthesized with several high‐yield steps. The specific molecular structure features of BM‐2F are planar molecular backbone and out‐of‐plane side chain, which is favorable for charge transport and can suppress the over‐aggregation. BM‐2F based neat and blend films display obvious face‐on molecular orientation. Specially, D18:BM‐2F based blend film can form good bicontinuous interpenetrating network. More excitingly, a power conversion efficiency of 16.15% was achieved with D18:BM‐2F based photovoltaic devices, which is the highest one based on NFREAs. Our researches manifest that NFREA is a promising direction for low‐cost and high‐performance organic solar cells. [ABSTRACT FROM AUTHOR]

Sequential deposition of the active layer in organic solar cells (OSCs) is favorable to circumvent the existing drawbacks associated with controlling the microstructure in bulk‐heterojunction (BHJ) device fabrication. However, how the processing solvents impact on the morphology during sequential deposition processes is still poorly understood. Herein, high‐efficiency OSCs are fabricated by a sequential blade coating (SBC) through optimization of the morphology evolution process induced by processing solvents. It is demonstrated that the device performance is highly dependent on the processing solvent of the upper layer. In situ morphology characterizations reveal that an obvious liquid–solid phase separation can be identified during the chlorobenzene processing of the D18 layer, corresponding to larger phase separation. During chloroform (CF) processing of the D18 layer, a proper aggregation rate of Y6 and favorable intermixing of lower and upper layers results in the enhanced crystallinity of the acceptor. This facilitates efficient exciton dissociation and charge transport with an inhibited charge recombination in the D18/CF‐based devices, contributing to a superior performance of 17.23%. These results highlight the importance of the processing solvent for the upper layer in the SBC strategy and suggest the great potential of achieving optimized morphology and high‐efficiency OSCs using the SBC strategy. [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]

Two isomeric fused‐ring electron acceptors F7TC‐1 and F7TC‐2 with different molecular symmetry are designed and synthesized, and the effect of molecular symmetry is studied. All side chains are located on the same side of the fused‐ring core in axisymmetric F7TC‐1, whereas they are evenly located on both sides of the fused‐ring core in centrosymmetric F7TC‐2. The molecular symmetry shows slight effects on the absorption spectra, energy levels, and bandgaps of the two molecules, but notable effects on crystallinity, molecular packing, film morphology, and device performance. F7TC‐1‐ and F7TC‐2‐based organic solar cells show power conversion efficiencies of 1.08% and 11.14%, respectively. Different molecular packing and film morphology lead to a big difference in device performance. [ABSTRACT FROM AUTHOR]

Two new fused‐ring electron acceptor (FREA) isomers with nonlinear and linear molecular conformation, m‐BAIDIC and p‐BAIDIC, are designed and synthesized. Despite the similar light absorption range and energy levels, the two isomers exhibit distinct electron reorganization energies and molecular packing motifs, which are directly related to the molecular conformation. Compared with the nonlinear acceptor, the linear p‐BAIDIC shows more ordered molecular packing and higher crystallinity. Furthermore, p‐BAIDIC‐based devices exhibit reduced nonradiative energy loss and improved charge transport mobilities. It is beneficial to enhance the open‐circuit voltage (VOC) and short‐current current density (JSC) of the devices. Therefore, the linear FREA, p‐BAIDIC yields a relatively higher efficiency of 7.71% in the binary device with PM6, in comparison with the nonlinear m‐BAIDIC. When p‐BAIDIC is incorporated into the binary PM6/BO‐4Cl system to form a ternary system, synergistic enhancements in VOC, JSC, fill factor (FF), and ultimately a high efficiency of 17.6% are achieved. [ABSTRACT FROM AUTHOR]

Exaggerated charge losses from excited to charge transfer (CT) and ground states in bulk heterojunction (BHJ) structures results in small voltages (< 1 V) for organic solar cells (OSCs). Characterizing morphology‐voltage loss correlations is difficult due to the complexity of BHJ structures but promises the realization of 20% efficiency for OSCs. By utilizing two similar non‐fullerene acceptors (NFA) in a ternary blend, a pseudo‐binary system is constructed to control the acceptor composition and donor‐acceptor (D‐A) miscibility. Within the framework of miscibility‐morphology controlled device photovoltaics, it is found that higher D‐A miscibility results in enhanced domain purity, which is associated with inefficient excitons dissociation and improves the excited and CT state emission, thereby resulting in enhanced electroluminescence efficiency to reduce the non‐radiative (NR) loss contribution to device voltage. The simple but effective composition mediated morphology control identifies domain purity as one key feature to lower the NR recombination in high quantum yield polymer/NFA blends. [ABSTRACT FROM AUTHOR]

The semitransparent and colorful properties of organic solar cells (OSCs) attract intensive academic interests due to their potential application in building integrated photovoltaics, wearable electronics, and so forth. The most straightforward and effective method to tune these optical properties is varying the componential ratio in the blend film. However, the increase in device transmittance inevitably sacrifices the photovoltaic performance because of severe carrier recombination that originates from discontinuous charge‐transport networks in the blend film. Herein, a strategy is proposed via the molecular‐doping strategy to overcome these shortcomings. It is discovered that p‐doping is able to release the trapped holes in segregated polymer domains leading to short‐circuit current enhancement, while n‐doping is more effective to fill the bandgap states producing a higher fill factor. More importantly, either type of doping improves the photovoltaic performance in the semitransparent photovoltaic devices. These discoveries provide a new pathway to breaking the compromise between the photovoltaic performance and optical transmittance in semitransparent OSCs, and hold promise for their future commercialization. [ABSTRACT FROM AUTHOR]

The donor/acceptor interaction in non‐fullerene organic photovoltaics leads to the mixing domain that dictates the morphology and electronic structure of the blended thin film. Initiative effort is paid to understand how these domain properties affect the device performances on high‐efficiency PM6:Y6 blends. Different fullerenes acceptors are used to manipulate the feature of mixing domain. It is seen that a tight packing in the mixing region is critical, which could effectively enhance the hole transfer and lead to the enlarged and narrow electron density of state (DOS). As a result, short‐circuit current (JSC) and fill factor (FF) are improved. The distribution of DOS and energy levels strongly influences open‐circuit voltage (VOC). The raised filling state of electron Fermi level is seen to be key in determining device VOC. Energy disorder is found to be a key factor to energy loss, which is highly correlated with the intermolecular distance in the mixing region. A 17.53% efficiency is obtained for optimized ternary devices, which is the highest value for similar systems. The current results indicate that a delicate optimization of the mixing domain property is an effective route to improve the VOC, JSC, and FF simultaneously, which provides new guidelines for morphology control toward high‐performance organic solar cells. [ABSTRACT FROM AUTHOR]

Increasing the photoluminescence quantum yield (PLQY) of narrow bandgap acceptors is of critical importance to suppress the nonradiative voltage loss (ΔVnr) in organic solar cells (OSCs). Herein, two acceptors, SM16 and SM16‐R, with an identical backbone but different terminal groups (norbornenyl modified 1,1‐dicyanomethylene‐3‐indanone and dimethyl substituted 1,1‐dicyanomethylene‐3‐indanone) are designed and synthesized. Compared with SM16‐R, SM16 displays better solubility, higher PLQY, and more favorable nanomorphology when blended with polymer donor PBDB‐T. PBDB‐T:SM16‐based OSCs yield a ΔVnr as low as 0.145 V. Using SM16 as the third component, a high power conversion efficiency of 17.1% is achieved in the ternary OSCs based on PBDB‐T:Y14:SM16, considerably higher than that of the binary devices based on PBDB‐T:Y14 or PBDB‐T:SM16. These results highlight that enhancing the PLQY of low bandgap acceptor via terminal group engineering strategy is highly effective to reduce ΔVnr of OSCs. [ABSTRACT FROM AUTHOR]

The rapid advance of fused‐ring electron acceptors (FREAs) has greatly promoted the leap‐forward development of organic solar cells (OSCs). However, the synthetic complexity of FREAs may be detrimental for future commercial applications. Recently, nonfused‐ring electron acceptors (NREAs) have been developed to be a promising candidate to maintain a rational balance between cost and performance, of which the cores are composed of simple fused rings (NREAs‐I) or nonfused rings (NREAs‐II). Moreover, "noncovalently conformational locks", are used as an effective strategy to enhance the rigidity and planarity of NREAs and improve device performance. Herein, a novel series of NREAs‐II (PhO4T‐1, PhO4T‐2, and PhO4T‐3) is constructed as a valuable platform for exploring the impact of the end group engineering on optoelectronic properties, intermolecular packing behaviors, and device performance. As a result, a high power conversion efficiency of 13.76% is achieved for PhO4T‐3 based OSCs, which is much higher than those of the PhO4T‐1 and PhO4T‐2‐based devices. Compared with several representative FREAs, PhO4T‐3 possesses the highest figure‐of‐merit value of 133.45 based on a cost‐efficiency evaluation. This work demonstrates that the simple‐structured NREAs‐II are promising candidates for low‐cost and high‐performance OSCs. [ABSTRACT FROM AUTHOR]

Three nonfused ring electron acceptors (NFREAs; 2Th‐2F, BTh‐Th‐2F, and 2BTh‐2F) with thieno[3,2‐b]thiophene bearing two bis(4‐butylphenyl)amino substituents as the core, 3‐octylthiophene or 3‐octylthieno[3,2‐b]thiophene as the spacer, and 3‐(1,1‐dicyanomethylene)‐5,6‐difluoro‐1‐indanone as the terminal group are designed and synthesized. The molar extinction coefficient of acceptors and the electron mobility of blend films gradually increase with increasing π‐conjugation length. Moreover, 2BTh‐2F displays a planar molecular conformation assisted by S···N and S···O intramolecular interactions. More importantly, the molecular stacking changes from 2D packing for the 2Th‐2F analog to 3D network packing for 2BTh‐2F. Due to these comprehensive merits, 2BTh‐2F:PBDB‐T‐based organic solar cells give a high power conversion efficiency of 14.53%. More impressively, when D18 is used as the donor polymer, the power conversion efficiency is further enhanced to 15.44%, which is the highest value reported for solar cells based on NFREAs. [ABSTRACT FROM AUTHOR]

Three asymmetric non‐fullerene acceptors (LL2, LL3, and LL4) are designed and synthesized with one norbornyl‐modified 1,1‐dicyanomethylene‐3‐indanone (CBIC) terminal group and one chlorinated 1,1‐dicyanomethylene‐3‐indanone (IC‐2Cl) terminal group. The three‐dimensional shape‐persistent CBIC terminal group can effectively enhance the solubility and tune the packing mode of acceptors. Compared with their symmetric counterparts (LL2‐2Cl, LL3‐2Cl, and LL4‐2Cl) bearing two IC‐2Cl terminals, the asymmetric acceptors show improved solubilities, giving rise to enhanced crystallinity and favored nanomorphology for charge transport in the blend films with PBDB‐T. Asymmetric acceptors based organic solar cells (OSCs) also show much lower voltage loss due to their higher ECT and EQEEL values. Therefore, they exhibit 17−27% higher power conversion efficiency (PCE) than OSCs based on the corresponding symmetric acceptors. Among these six acceptors, LL3 with a central benzotriazole core shows the best PCE of 16.82% with an outstanding Jsc of 26.97 mA cm−2 and a low nonradiative voltage loss (ΔVnr) of 0.18 V, the best values for PBDB‐T based OSCs. The Jsc and ΔVnr also represent the best reported for asymmetric non‐fullerene acceptors‐based OSCs to date. The results demonstrate that the combination of the unique CBIC terminal group with the asymmetric strategy is a promising way to enhance the performance of OSCs. [ABSTRACT FROM AUTHOR]

The electron donor/acceptor (D/A) heterojunction is the core for photocharge generation and recombination in organic photovoltaics (OPVs). Developing practical methods for the D/A heterojunction modification remains challenging and is rarely discussed in OPV research. Herein, the roles of molecular doping at the D/A heterojunction in the charge‐transfer exciton dissociation and detailed energy loss are investigated, and new insights are gained into the functions of doping on the OPV performance. Heterojunction doping simultaneously enhances all three OPV parameters, especially the short‐circuit current (Jsc). It is shown that the Jsc improvement is due to the combined effects of strengthened electric field and reduced activation energy, which is regulated via an entropy‐related mechanism. The performance enhancement is further demonstrated in homojunction devices showing the great potential of interfacial doping to overcome the intrinsic limitation between high Jsc and open‐circuit voltage (Voc) in OPVs. [ABSTRACT FROM AUTHOR]

Morphology evolution kinetics at multi‐scale regime is a challenging problem which is critical for industrial fabrication of high‐performance organic solar cells (OSCs). An innovative strategy utilizing a patterned blade to print non‐fullerene (NF) based devices in ambient conditions is demonstrated. A specially designed patterned blade with micro‐cylinder arrays exhibit a reasonable control over the fluid flow at high extensional and shear strain rate to enhance lateral mass transport during blade‐coating. Comparison of patterned and normal blade in printing polymer:NF blend film at different speeds reveals interesting avenues to optimize the blend films morphology. Patterned blade printed PM6:Y6 films yield a PCE of 15.93% as compared to 14.55% from a normal blade. Through in situ and ex situ morphology characterization techniques, the use of patterned blades induce conformational changes in PM6 chains, enabling Y6 to crystallize faster and more efficiently. Such improved blend morphology enables favorable charge transfer and transport to realize superior device performance. A lower stick‐slip effect at the macro‐scale with the patterned blade results in a smoother film promoting device reproducibility. Applications in efficient large‐scale devices, confirming the choice of patterned blade design are reported. The efforts collaborating device engineering, morphology evolution kinetics would enable reproducibility and eased commercialization of OSCs at large scale. [ABSTRACT FROM AUTHOR]

Isomeric effects play a crucial role in regulating electronic properties, molecular packing, and device performance of organic semiconductors. Herein, a series of unfused‐ring electron acceptor (UREA) regioisomers (NOF‐1, NOF‐2, and NOF‐3), which are constructed using 2,6‐α‐, 1,5‐β‐, and 3,7‐β‐type naphthalene cores, are successfully synthesized and characterized. The regioisomeric effects on geometries, photophysics, electrical properties, molecular packing behaviors, charge transport properties, blend film morphologies, and photovoltaic performance are systematically studied. As a result, the PBDB‐T:NOF‐3‐based device delivers a power conversion efficiency (PCE) of 11.58% due to its more balanced charge mobility, efficient exciton dissociation, less charge recombination, and favorable film morphology. These findings encourage further attention to the regioisomeric effects to design high‐performance UREAs. [ABSTRACT FROM AUTHOR]

Fused‐ring electron acceptors have made significant progress in recent years, while the development of fully non‐fused ring acceptors has been unsatisfactory. Here, two fully non‐fused ring acceptors, o‐4TBC‐2F and m‐4TBC‐2F, were designed and synthesized. By regulating the location of the hexyloxy chains, o‐4TBC‐2F formed planar backbones, while m‐4TBC‐2F displayed a twisted backbone. Additionally, the o‐4TBC‐2F film showed a markedly red‐shifted absorption after thermal annealing, which indicated the formation of J‐aggregates. For fabrication of organic solar cells (OSCs), PBDB‐T was used as a donor and blended with the two acceptors. The o‐4TBC‐2F‐based blend films displayed higher charge mobilities, lower energy loss and a higher power conversion efficiency (PCE). The optimized devices based on o‐4TBC‐2F gave a PCE of 10.26 %, which was much higher than those based on m‐4TBC‐2F at 2.63 %, and it is one of the highest reported PCE values for fully non‐fused ring electron acceptors. [ABSTRACT FROM AUTHOR]

Sequential deposition has great potential to achieve high performance in organic solar cells due to the resulting well‐controlled vertical phase separation. In this work, double bulk heterojunction organic solar cells are fabricated by sequential‐blade cast in ambient conditions. Probed by the in situ grazing incidence X‐ray diffraction and in situ UV–vis absorption measurements, the seq‐blade system exhibits a different tendency from each of the binary films during the film formation process. Due to the extensive aggregation of FOIC, the binary PBDB‐T:FOIC film displays a strong and large phase separation, resulting in low current density (Jsc) and unsatisfactory power conversion efficiency. In the seq‐blade cast system, the bottom layer PBDB‐T:IT‐M produces many crystal nuclei for the top layer PBDB‐T:FOIC, so the PBDB‐T molecules are able to crystallize easily and quickly. Balanced crystallization kinetics between polymer and small molecule and an ideal percolation network in the film are observed. In addition, the balanced crystallization kinetics are favorable toward realizing lower recombination loss through charge transport processes. [ABSTRACT FROM AUTHOR]

Single‐layered organic solar cells (OSCs) using nonfullerene acceptors have reached 16% efficiency. Such a breakthrough has inspired new sparks for the development of the next generation of OSC materials. In addition to the optimization of electronic structure, it is important to investigate the essential solid‐state structure that guides the high efficiency of bulk heterojunction blends, which provides insight in understanding how to pair an efficient donor–acceptor mixture and refine film morphology. In this study, a thorough analysis is executed to reveal morphology details, and the results demonstrate that Y6 can form a unique 2D packing with a polymer‐like conjugated backbone oriented normal to the substrate, controlled by the processing solvent and thermal annealing conditions. Such morphology provides improved carrier transport and ultrafast hole and electron transfer, leading to improved device performance, and the best optimized device shows a power conversion efficiency of 16.88% (16.4% certified). This work reveals the importance of film morphology and the mechanism by which it affects device performance. A full set of analytical methods and processing conditions are executed to achieve high efficiency solar cells from materials design to device optimization, which will be useful in future OSC technology development. [ABSTRACT FROM AUTHOR]

The surface defects of solution-processed ZnO films lead to various intragap states. When the solution-processed ZnO films are used as electron transport interlayers (ETLs) in inverted organic solar cells, the intragap states act as interfacial recombination centers for photogenerated charges and thereby degrade the device performance. Here, a simple passivation method based on ethanedithiol (EDT) treatment is demonstrated, which effectively removes the surface defects of the ZnO nanocrystal films by forming zinc ethanedithiolates. The passivation by EDT treatment modulates the intragap states of the ZnO films and introduces a new intragap band. When the EDT-treated ZnO nanocrystal films are used as ETLs in inverted organic solar cells, both the power conversion efficiency and stability of the devices are improved. The control studies show that the solar cells with EDT-treated ZnO films exhibit reduced charge recombination rates and enhanced charge extraction properties. These features are consistent with the fact that the modulation of the intragap states results in reduction of interfacial recombination as well as the improved charge selectivity and electron transport properties of the ETLs. It is further demonstrated that the EDT treatment-based passivation method can be extended to ZnO films deposited from sol-gel precursors. [ABSTRACT FROM AUTHOR]

The effects of cathode modification by a conjugated polymer interlayer PFPA1 on the performance of reversed organic solar cells (substrate/cathode/active layer/transparent anode) based on different active material systems and different substrate electrodes are systematically investigated. A reduction of the work function irrespective of the substrate cathode used is observed upon the deposition of the PFPA1 interlayer, which is further related to an improved built-in electric field and open-circuit voltage. The amphiphilic character of the PFPA1 interlayer alters the surface energy of the substrate cathode, leading to the formation of a better active layer morphology aiding efficient exciton dissociation and photocurrent extraction in the modified solar cells. Hence, internal quantum efficiency is found to be significantly higher than that of their unmodified counterparts, while optically, the modified and unmodified solar cells are identical. Moreover, the deep highest occupied molecular orbital (HOMO) of the PFPA1 interlayer improves the selectivity for all investigated substrate cathodes, thus enhancing the fill factor. [ABSTRACT FROM AUTHOR]

Efficient dielectric scatterers based on a mixture of TiO2 nanoparticles and polydimethylsiloxane are demonstrated for light trapping in semitransparent organic solar cells. An improvement of 80% in the photocurrent of an optimized semitransparent solar cell is achieved with the dielectric scatterer with ≈100% diffuse reflectance for wavelengths larger than 400 nm. For a parallel tandem solar cell, the dielectric scatterer generates 20% more photocurrent compared with a silver mirror beneath the cell; for a series tandem solar cell, the dielectric scatterer can be used as a photocurrent balancer between the subcells with different photoabsorbing materials. The power conversion efficiency of the tandem cell in series configuration with balanced photocurrent in the subcells exceeds that of an optimized standard solar cell with a reflective electrode. The characteristics of polydimethylsiloxane, such as flexibility and the ability to stick conformably to surfaces, also remain in the dielectric scatterers, which makes the demonstrated light trapping configuration highly suitable for large scale module manufacturing of roll-to-roll printed organic single- or tandem-junction solar cells. [ABSTRACT FROM AUTHOR]

Designing and synthesizing narrow band gap acceptors that exhibit high photoluminescence quantum yield (PLQY) and strong crystallinity is a highly effective, yet challenging, approach to reducing non‐radiative energy losses (▵Enr) and boosting the performance of organic solar cells (OSCs). We have successfully designed and synthesized an A–D–A type fused‐ring electron acceptor, named DM‐F, which features a planar molecular backbone adorned with bulky three‐dimensional camphane side groups at its central core. These bulky substituents effectively hinder the formation of H‐aggregates of the acceptors, promoting the formation of more J‐aggregates and notably elevating the PLQY of the acceptor in the film. As anticipated, DM‐F showcases pronounced near‐infrared absorption coupled with impressive crystallinity. Organic solar cells (OSCs) leveraging DM‐F exhibit a high EQEEL value and remarkably low ▵Enr of 0.14 eV‐currently the most minimal reported value for OSCs. Moreover, the power conversion efficiency (PCE) of binary and ternary OSCs utilizing DM‐F has reached 16.16 % and 20.09 %, respectively, marking a new apex in reported efficiency within the OSCs field. In conclusion, our study reveals that designing narrow band gap acceptors with high PLQY is an effective way to reduce ▵Enr and improve the PCE of OSCs. [ABSTRACT FROM AUTHOR]

In addition to high power conversion efficiency (PCE) and good stability, the low-cost of photovoltaic materials is also very important for the practical application of organic solar cells (OSCs). Herein, we synthesized a carboxylate substituted pyrazine-based electron-deficient building block (DTCPz) with a simple structure and low synthetic cost, and then developed a novel wide bandgap polymer donor PFBCPZ. Due to the synergistic electron-withdrawing effects of the fluorination in donor unit (BDT-TF) and esterification and C=N double-bond in DTCPz unit, PFBCPZ shows a deeper HOMO level of −5.60 eV, a strong intermolecular π-π interaction, good crystallinity and stacking, and high hole-mobility of 2.11 × 10−3 cm2 V−1 s−1. Matched with a low bandgap acceptor IT-4F, excellent charge transfer, weak recombination, and small non-radiative energy loss in OSCs was achieved, resulting in an impressive fill factor of 0.785 and a high open-circuit voltage of 0.92 V. As a result, a PCE of up to 15.3% is obtained in OSCs, which is the highest value in the IT-4F-based binary OSCs so far and indicates that low-cost DTCPz with a simple structure is a promising building block to construct high-performance polymer donors for application in efficient OSCs. [Display omitted] • A novel wide bandgap polymer donor PFBCPZ was synthesized. • The novel building block (DTCPz) showed easily synthesized routs with cheap raw material. • The OSC based on PFBCPZ:IT-4F exhibited excellent performance with 15.3% efficiency. • The efficiency is the highest value in the IT-4F-based binary OSCs so far. [ABSTRACT FROM AUTHOR]

Simultaneously broadening the spectral response and reducing the energy loss are challenging tasks in the material design of organic solar cells (OSCs). Herein, a novel asymmetrically noncovalently fused-ring electron acceptor (NFEA) with unilateral alkylthio-substituted thiophene π-bridge, namely IDST-4F, is synthesized. IDST-4F exhibits a broader absorption, higher-lying energy levels, larger dipole moments and suppressed crystallinity than its symmetric counterpart (ID-4F) without the π-bridge. Compared to the devices of PM6:ID-4F, the optimized PM6:IDST-4F-based devices display simultaneously enhanced current density and photovoltage, resulting in an excellent power conversion efficiency (PCE) of 14.3%, which is the highest value among the OSCs based on NFEAs reported in the literature to date. More importantly, the PM6:IDST-4F-based OSCs possess excellent thermal stability with 82% of the initial PCE after thermal treatment at 150 °C for 1200 min. In summary, this study indicates that asymmetrically NFEAs are promising to achieve high efficiency with excellent thermal stability. Image 1 • A novel acceptor IDST-4F, consisting of an asymmetric fused-ring core locked by a noncovalent interaction is developed. • The PM6:IDST-4F-based OSCs display a significantly improved efficiency of 14.3%. • The PM6:IDST-4F-based PSCs exhibit lower energy loss of 0.59 eV and excellent thermal stability. [ABSTRACT FROM AUTHOR]

Non-Fullerene Acceptors: Efficient Organic Solar Cell with 16.88% Efficiency Enabled by Refined Acceptor Crystallization and Morphology with Improved Charge Transfer and Transport Properties (Adv. Keywords: 2D electron transport; multilength-scaled morphology; nonfullerene acceptors; organic solar cells; power conversion efficiency EN 2D electron transport multilength-scaled morphology nonfullerene acceptors organic solar cells power conversion efficiency 1 1 1 05/14/20 20200512 NES 200512 In article number 1904234, Feng Liu and co-workers report a detailed structure-performance relationship to help understand the success of Y6 non-fullerene acceptors. 2D electron transport, multilength-scaled morphology, nonfullerene acceptors, organic solar cells, power conversion efficiency. [Extracted from the article]

A series of alkyl, alkoxyl, and alkylthio substituted A–π–D–π–A type nonfullerene acceptors (NFAs) IDTCN‐C, IDTCN‐O, and IDTCN‐S are designed and synthesized. The introduction of a lateral side chain at the outer position of the π bridge unit can endow the terminal moiety with a confined planar conformation due to the steric hindrance. Thus, compared with nonsubstituted NFA (IDTT2F), these acceptors tend to form favorable face‐on orientation and exhibit strong crystallinity as verified with grazing‐incidence wide‐angle X‐ray scattering measurement. Moreover, the variation of side chain can significantly change the lowest unoccupied molecular orbital (LUMO) energy level of acceptors. As state‐of‐the‐art NFAs, a power conversion efficiency of 13.28% (Voc = 0.91 V, Jsc = 19.96 mA cm−2, and FF = 73.2%) is obtained for the as‐cast devices based on IDTCN‐O, which is among the highest value reported in literature. The excellent photovoltaic performance for IDTCN‐O can be attributed to its slightly up‐shifted LUMO level and more balanced charge transport. This research demonstrates side chain engineering is an effective way to achieve high efficiency organic solar cells. [ABSTRACT FROM AUTHOR]

A surface passivation method for solution‐processed ZnO films based on small molecule ethanedithiol (EDT) treatment is reported by Yizheng Jin, Baoquan Sun, Feng Gao, and co‐workers in article number 1401606. The passivation using EDT treatment on ZnO effectively removes the surface defects and modulates the intragap states with the introduced intragap band. The device performances of inverted organic solar cells based on EDT‐treated, solution‐processed, ZnO electron‐transporting interlayers are significantly improved due to reduced interface recombination and enhanced charge extraction properties. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: By simplifying the π‐bridge unit, a nonfused ring electron acceptor (NFREA) BM‐2F was designed and synthesized with several high‐yield steps. The specific molecular structure features of BM‐2F are planar molecular backbone and out‐of‐plane side chain, which is favorable for charge transport and can suppress the over‐aggregation. BM‐2F based neat and blend films display obvious face‐on molecular orientation. Specially, D18:BM‐2F based blend film can form good bicontinuous interpenetrating network. More excitingly, a power conversion efficiency of 16.15% was achieved with D18:BM‐2F based photovoltaic devices, which is the highest one based on NFREAs. Our researches manifest that NFREA is a promising direction for low‐cost and high‐performance organic solar cells. [ABSTRACT FROM AUTHOR]

In this work, we successfully applied a fullerene derivative PC 71 BM as the second acceptor in PM6:BTP-BO-4Cl bulk heterojunction organic solar cell system. The device performance can be remarkably enhanced from 16.65% of the PM6:BTP-BO-4Cl binary system to approaching 17.4% of the ternary system with just low PC 71 BM loading. Detailed investigation revealed that introduction of small amount of PC 71 BM can improve the molecular aggregation and film morphology, thus display better exciton dissociation and charge transport. [Display omitted] In this work, we introduced a fullerene acceptor (PC 71 BM) into the binary photo-active layer based on a polymer donor (PM6) and a non-fullerene small molecular acceptor (BTP-BO-4Cl), and as a consequence, the ternary organic solar cells realized a high-power conversion efficiency of 17.39% compared to 16.65% in binary solar cells. The performance enhancement was found to be due to the optimized morphology and hence balanced hole and electron mobilities, which is responsible for the suppressed charge recombination and hence high photocurrent in solar cells. In addition, PC 71 BM shows the complementary absorption with PM6 and BTP-BO-4Cl, which can broaden the absorption range of the photo-active layer and hence more photons from the sunlight can be utilized. Besides, PC 71 BM shows the cascade energy level alignment between PM6 and BTP-BO-4Cl, which is helpful for charge transfer from donor to acceptor. All these merits explain the high performance in ternary solar cells, and also demonstrate that ternary photovoltaics adopting non-fullerene acceptor with the fullerene acceptor as small amount of additive is an efficient strategy to gain high performing organic solar cells. [ABSTRACT FROM AUTHOR]

• Acceptor fluorination leads to increased voltage losses in organic solar cells. • The increased voltage loss is associated with increased reorganization energy. • A side chain modification strategy is proposed to address the voltage loss issue. Acceptor fluorination is a commonly employed molecular modification strategy aimed at enhancing the quantum efficiency and charge carrier transport properties of organic solar cells. However, this approach often leads to a significant reduction in the open-circuit voltage (V oc) of the solar cells, thereby limiting their overall performance. In this study, we investigate the limitation of V oc in organic solar cells based on fluorinated acceptors. Our investigation reveals that the reduced V oc can be attributed to increased voltage losses (V loss), primarily arising from more significant non-radiative voltage losses originating from a decline in the external quantum efficiency of electroluminescence (EQE EL). Furthermore, we establish that the reduced EQE EL is a result of deteriorated molecular packing, which leads to an elevated reorganization energy. To address the high V loss and limited performance observed in solar cells utilizing fluorinated acceptors, we propose a strategy involving acceptor side-chain modifications. These results provide new insights into enhancing the performance of organic solar cells. [ABSTRACT FROM AUTHOR]

• Increasing donor side chain size leads to reduced CT dissociation efficiency. • Increasing acceptor side chain size results in reduced device voltage losses. • Highest PCE is realized when both the donor and acceptor are with large side chains. Increasing the size of the side chains of the donor or the acceptor materials is a highly effective strategy to reduce voltage losses, and increase the open-circuit voltage (Voc) of organic solar cells (OSCs). However, higher Voc does not necessarily translate to improved overall performance. To optimize side-chains and improve the performance of OSCs, the origin of the impact of the increased size of the donor and/or acceptor side side-chains size on the performance of OSCs is investigated. The study demonstrates that increasing the size of donor side chains can increase Voc, but it can also lead to deteriorated molecular packing, limiting overall solar cell performance. On the other hand, increasing the size of acceptor side chains can also increase Voc and improve molecular packing properties of the active layer, resulting in improved solar cell performance. Finally, the study shows that the best photovoltaic performance is achieved when both the donor and acceptor have large side chains. This research establishes the relationship between side chains of active materials, molecular packing properties, and the energetics of the donor/acceptor active layer, which is crucial for overcoming performance bottlenecks in OSCs. [ABSTRACT FROM AUTHOR]

A new nonfused ring electron acceptor PDI-DO-2F is designed and synthesized by attaching perylenediimide (PDI) unit as a pendent group to the central donor core. Compared with the control molecule DO-2F , the introduction of PDI lateral substituent can greatly enhance the solubility and decrease the crystallinity of the resulted acceptor. The PBDB-T :PDI-DO-2F blend film exhibits a much better morphology with higher and more balanced carrier mobility in contrast to PBDB-T :DO-2F one. PDI-DO-2F based organic solar cells (OSCs) give a power conversion efficiency (PCE) of 11.78%, higher than DO-2F based ones (9.82%). Furthermore, PDI-DO-2F based OSCs shows a Δ E non-rad value of 0.23 eV, which is significantly lower than the DO-2F based ones (0.28 eV). More importantly, the addition of PDI-DO-2F as the third component to the PBDB-T :DO-2F binary system can optimize the morphology of blend films and improve the shelf stability of devices. And the PBDB-T :DO-2F : PDI-DO-2F based ternary OSCs achieve a higher PCE of 13.82%. [Display omitted] • A new nonfused ring electron acceptor is designed and synthesized. • PDI unit as a pendent group can greatly enhance the solubility and decrease the crystallinity of the acceptor. • Significantly different power conversion efficiencies of 9.82%, 11.78% and 13.82% are achieved. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three small molecular acceptors were designed and synthesized. • Noncovalent Conformational Locks and Side-Chain Engineering can adjust the properties of acceptors. • Significantly different power conversion efficiencies of 12.09%, 12.30% and 14.25% are achieved. Three novel small molecular acceptors (SMAs) BO-2F , BO-C8-2F and BO-C2C6-C8-2F were designed and synthesized. These acceptors all possess planar molecular backbone because of the introduction of intramolecular noncovalent interaction. Among them, BO-C2C6-C8-2F with four side chains, which has the highest solubility, can form more appropriate nanomorphology when blending with PBDB-T. Hence, organic solar cells (OSCs) based on PBDB-T: BO-C2C6-C8-2F displayed an outstanding power convesion efficiency (PCE) of 14.25%, which is higher than BO-2F and BO-C8-2F based ones. To the best of our knowledge, the PCE of 14.25% is one of the highest for the OSCs based on A-π-D-π-A type SMAs. Our results have demonstrated that the combination of side-chain engineering and intramolecular conformation lock has a great prospect in the design of high performance SMAs for OSCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • We can modularly synthesize two fully nonfused ring acceptors with only four high-yield steps. • A simple fully nonfused ring electron acceptor can achieve a high PCE of over 12%. • The high FOM of 4T-OEH indicates its great potential for future practical applications. We designed two simple fully nonfused ring electron acceptors 4T-OEH and 4T-EH with 3,4-bis(alkoxy)thiophene and 3,4-dialkylthiophene π-bridge units, respectively, which can be modularly synthesized with only four high-yield steps. With the help of intramolecular S-O noncovalent interaction, 4T-OEH tends to form a planar molecular backbone, which is beneficial for the electron delocalization and charge transport. Besides, the neat 4T-OEH film displays a more ordered molecular packing and obviously red-shifted absorption after thermal annealing. Compared with 4T-EH , 4T-OEH based devices can form more homogenous phase morphology, higher and more balanced hole and electron mobilities. The optimal OSCs based on 4T-OEH can generate an excellent PCE of 12.12%, which is much higher than 4T-OEH based ones (7.36%). It is worth noting that the figure-of-merit values of 4T-OEH is much higher than the star acceptors (ITIC and Y6), demonstrating its high potential for future practical application. Our work has demonstrated that we can tune the backbone planarity, solubility and packing behavior of acceptor molecules via optimizing their lateral substituents to obtain high efficiency and low-cost fully nonfused ring electron acceptors. [ABSTRACT FROM AUTHOR]

• Minor terminal and central changes endow DO-2F and FO-N complementary absorption. • Asymmetrical FO-N effectively suppress the self-aggregation of DO-2F. • Acceptor alloy is found between the FO-N and DO-2F. • Alloy state acceptors produce suitable morphology with reduced V nr of 0.23 eV. • FO-N is an excellent third component for highly efficient OSCs of 14.10% Nonfused ring acceptors have shown great potential for future commercial applications of organic solar cells (OSCs) due to their simple structure and low synthetic costs. Herein, a novel asymmetrical nonfused ring acceptor FO-N with one branched lateral chain and one fluoro substituent at the central phenylene core was designed and introduced into PBDB-T : DO-2F binary system to fabricate high-efficiency ternary OSCs. The high-lying LUMO level of FO-N is conducive to improve V oc for ternary devices. More importantly, the introduction of FO-N as the third component can efficiently improve the compatibility of the ternary system via tuning the crystal size and optimizing the blend film morphology, which is beneficial to charge separation and reduced the non-radiative energy loss (Δ E nonrad). Finally, the ternary device achieved a low Δ E nonrad of 0.23 eV and a greatly improved PCE of 14.10% and with a V oc of 0.88 V, a J sc of 21.48 mA/cm2 and an FF of 74.41%. These results imply that the asymmetric nonfused ring acceptor design strategy is an effective way for optimizing the photovoltaic performance of highly crystallized blend system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two isomeric fully nonfused ring electron acceptors are designed and synthesized. • The location of diphenylamine units can adjust the properties of acceptors. • Significantly different power conversion efficiencies of 12.83% and 0.43% are achieved. We have designed and synthesized two fully nonfused ring electron acceptors LW-in-2F and LW-out-2F with two diphenylamine side chains at different positions of the bithiophene core. The two diphenylamine side chains of LW-in-2F and LW-out-2F are at the outside and inside positions of the central bithiophene unit, respectively. The performance of LW-in-2F and LW-out-2F -based devices is very different, the photoelectric conversion efficiency (PCE) of LW-out-2F -based device is as high as 12.83%, while the efficiency of LW-in-2F -based device is only 0.43%. By GIWAXS test, we found that the change of diphenylamine position affects the way of molecular arrangement. When the diphenylamine side chain is located on the outer side of the central core, the molecular arrangement shows face-on orientation, which is beneficial for perpendicular charge transport, resulting in high and balanced charge mobilities and high PCE. [ABSTRACT FROM AUTHOR]