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The state‐of‐the‐art power conversion efficiency (PCE) of organic solar cells (OSCs) is typically achieved in the devices fabricated by toxic halogen solvents with complex post‐treatment processes in strictly inert atmosphere. Developing suitable processing method for printing in ambient air using eco‐friendly solvents with continuous solution supply and fabricating efficient devices without any post‐treatment are intensively desired. Controlling the crystallization kinetics to fine‐tune the acceptor's assembly behavior with a second donor for favorable morphological evolution is an effective approach to achieve above requirements. Herein, a kinetics‐controlling strategy is implemented by introducing a strong crystalline small molecule, BTR‐Cl, to enhance the crystallinity of acceptors. The combined in situ spectra characterizations revealed that the earlier aggregation of acceptor and modulation in conformation of PM6 can be achieved. This unique aggregation behavior facilitated enhanced film crystallization with reduced paracrystallinity of π–π stacking, resulting in improved charge transport and inhibited charge recombination. An outstanding PCE of 17.50% is obtained for the device processed with o‐xylene via ambient air printing without any post‐treatment. More significantly, efficient all‐printed inverted devices and large‐area modules are prepared. The generalization of this strategy has been confirmed in other efficient systems, suggesting a great potential for universally fabricating high‐efficiency and eco‐friendly OSCs. [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 intra and intermolecular interactions (J‐ and H‐type aggregation) in the conjugated polymer films are found to readily facilitate the electron and hole transport, respectively. However, how those different aggregation types influence the photocurrent generation at the heterojunction is still mysterious, especially for the newly developed semicrystalline conjugated polymers. Here, the prototypical copolymer PM6 is used to tune the relative content of aggregation types with various halogen‐free processing solvents. Various measurements reveal that the toluene‐processed PM6 film exhibits the increased H‐aggregates and crystallinity in the π–π stacking direction compared to its o‐xylene‐ and trimethylbenzene (TMB)‐processed counterparts. This is partly resulted from the weak steric effect and good solubility in the PM6 solution prepared with toluene, which strengthens the intermolecular interaction of adjacent polymer segments. After analyzing the photovoltaic properties of PM6/Y6 bilayer devices, the faster charge carrier transport, smaller charge recombination, lower energy losses, and interfacial energetic disorder can be observed in the toluene‐processed device, leading to the synergistically improved short‐circuit current density (JSC) and open‐circuit voltage (VOC). These findings indicate the control of the molecular packing structure in terms of aggregation types is a powerful strategy to promote the photocurrent generation process at the conjugated polymer‐based heterojunction. [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]

Thick active layers in organic solar cells (OSCs) have a great promise of enhancing light absorption and providing pinhole‐free films for large‐scale fabrication. Since charge carriers in thick films need a longer transporting path in the vertical direction to the electrode than in thin films, modulation of the active layer morphology in thick films is highly required for effective charge transport. Herein, thin‐film (≈110 nm) and thick‐film (≈300 nm) OSCs based on a PM6:IT‐4 F film are fabricated by blade coating with various additive contents. It is found that the optimized thick‐film device needs more additives than the optimized thin‐film device. The addition of more additives in thick‐films promotes vertical component distribution and enhances the crystallization, resulting in efficient charge transport with reduced charge recombination and electron (or hole) accumulation within the thick active layer. These results are also confirmed by PM6:Y6‐based devices, in which optimized thin‐film and thick‐film devices exhibit power conversion efficiency (PCE) of 16.69% and 14.91% at the additive contents of 0.3% and 0.6%, respectively. Encouragingly, thick‐film device with 0.6% additive has a narrow distribution of PCE values, and high PCEs of 13.94% and 13.05% are obtained for the large‐area (1 cm2) rigid and flexible thick‐film OSCs, showing great application prospect. [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]

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]

As a predominant fabrication method of organic solar cells (OSCs), casting of a bulk heterojunction (BHJ) structure presents overwhelming advantages for achieving higher power conversion efficiency (PCE). However, long‐term stability and mechanical strength are significantly crucial to realize large‐area and flexible devices. Here, controlling blend film morphology is considered as an effective way toward co‐optimizing device performance, stability, and mechanical properties. A PCE of 12.27% for a P‐i‐N‐structured OSC processed by sequential blade casting (SBC) is reported. The device not only outperforms the as‐cast BHJ devices (11.01%), but also shows impressive stability and mechanical properties. The authors corroborate such enhancements with improved vertical phase separation and purer phases toward more efficient transport and collection of charges. Moreover, adaptation of SBC strategy here will result in thermodynamically favorable nanostructures toward more stable film morphology, and thus improving the stability and mechanical properties of the devices. Such co‐optimization of OSCs will pave ways toward realizing the highly efficient, large‐area, flexible devices for future endeavors. [ABSTRACT FROM AUTHOR]

Abstract: Due to the attraction of optimizing the electronic structure beyond chemical synthesis, molecular doping has recently aroused wide interest in the field of organic solar cells. However, the selection of limited dopants confines its successful application. Inspired by the Lewis base characteristics of the photovoltaic materials, the Lewis acid as novel dopant is introduced in organic solar cells. In both fullerene and nonfullerene based blends, Lewis acid doping leads to increased photovoltaic performance. Detailed experiments reveal that Lewis acid doping has a synergistic effect on modifying the polymer's electronic properties and the acceptor's nanostructure even at low doping concentration, and these are simultaneously responsible for the device improvements. Based on the mechanism studies, it is proposed that the Lewis acid‐doped polymers anions produce induced dipole on the acceptor, this increases the intermolecular interaction and facilitates the morphology optimization. It is believed that the synergistic effect by Lewis acid doping greatly expands the application of doped organic solar cells, in concert with other existing methods to yield higher efficiency values. [ABSTRACT FROM AUTHOR]