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Ternary architecture is a promising strategy to further boost the performance of organic solar cells (OSCs). Reducing the bandgap of the active layer materials not only widens the absorption wavelength range and enhances the short‐circuit current (Jsc) of the OSC, but also decreases the open‐circuit voltage (Voc) of the device, leading to a trade‐off situation for the optimization of the material system. Herein, a small‐molecule donor BTID‐2F, featuring a narrower bandgap than that of PM6, is introduced into a PM6:Y6 based system. The redshift in external quantum efficiency indicates the narrower bandgap and better aggregation in the ternary blends than those of binary ones. Interestingly, lower energy disorder and energy loss are also attained for the ternary devices, leading to higher Voc. Furthermore, owing to the suppressed recombination and morphological optimization, a simultaneous enhancement in the Jsc and fill factor boosts the power conversion efficiency (PCE) of ternary OSC to 17.9% compared to 16.62% for the binary device. Likewise, replacing the acceptor with the L8‐BO molecule further improves the ternary PCE to 18.52%. This work indicates an emerging approach for fabricating high‐performance ternary OSCs with a decreased bandgap and increased Voc. [ABSTRACT FROM AUTHOR]

Bulk heterojunction (BHJ) morphologies are vital to the device performance of organic solar cells (OSCs), including phase separation in lateral and vertical directions. However, the morphology developed from the blend solution is not easily predicted and controlled, especially in the vertical direction, because the BHJ morphology is kinetically frozen during the rapid solvent evaporation process. Here, a simple approach to control BHJ morphologies with optimized phase distribution for small molecule:[6,6]-phenyl-C71-butyric acid methyl ester (PC71 BM) blends by enhancing the substrate temperature during the spin-coating process. Three molecules with various fluorine atoms in the end acceptor units are selected. The relationship among molecular structures, substrate temperature effects on the morphology, and device performances are symmetrically investigated. Low temperature induces a multiple-sublayer-like architecture with significantly varied distributions of composition, morphology, and localized state energy, while high processing temperature induces more uniform film. The short-circuit current, open-circuit voltage, and fill factor of the devices are tuned with synergic improvement of efficiency toward over 10% and 11% for conventional and inverted devices. This work reveals the origination of vertical phase segregation, and provides a facile strategy to optimize the hierarchical phase separation for enhancing the performance of OSCs. [ABSTRACT FROM AUTHOR]

Compared with nonfullerene‐based polymer solar cells, all‐small‐molecule solar cells normally show low power conversion efficiencies (PCEs) due to their low fill factors (FFs). Molecular stacking orientation and phase separation are the main factors affecting the performance of all‐small‐molecule solar cells. In this work, two liquid‐crystalline small‐molecule donors are designed and synthesized and a novel nonfullerene acceptor with good crystallinity developed. Owing to the face‐on orientation of the component molecules and appropriate phase separation in the active layer, a high FF of over 70% and a PCE of 10.7% are obtained from the resulting solar cells; these values are among the best obtained thus far for all‐small‐molecule solar cells. The high FF reported here is significant for a further design of high‐performance all‐small‐molecule solar cells. The combination of a liquid‐crystalline small‐molecule donor and a nonfullerene acceptor with good crystallinity provides appropriate phase separation and molecular stacking orientation for all‐small‐molecule solar cells. The fill factors and power conversion efficiencies (PCEs) are obviously improved in the proposed systems, and the maximum PCE reaches 10.7%. The results are significant for the construction and development of all‐small‐molecule solar cells. [ABSTRACT FROM AUTHOR]