A series of polymer acceptors PF2-DTC, PF2-DTSi, and PF2-DTGe with identical molecular backbone but different central bridging atoms in tricyclic-fused donor units were developed. In all-PSCs, the PF2-DTSi-based blend film exhibited excellent mechanical robustness with an impressively high PCE of up to 10.77%. Moreover, the flexible solar cell based on this blend retained >90% of its initial PCE after bending and relaxing 1,200 times at a bending radius of 4 mm.

Despite the significant progresses made in all-polymer solar cells (all-PSCs) recently, the relatively low short-circuit current density (J sc ) and large energy loss are still quite difficult to overcome for further development. To address these challenges, we developed a new class of narrow-bandgap polymer acceptors incorporating a benzotriazole (BTz)-core fused-ring segment, named the PZT series. Compared to the commonly used benzothiadiazole (BT)-containing polymer PYT, the less electron-deficient BTz renders PZT derivatives with significantly red-shifted optical absorption and up-shifted energy levels, leading to simultaneously improved J sc and open-circuit voltage in the resultant all-PSCs. More importantly, a regioregular PZT (PZT-γ) has been developed to achieve higher regiospecificity for avoiding the formation of isomers during polymerization. Benefiting from the more extended absorption, better backbone ordering, and more optimal blend morphology with donor component, PZT-γ-based all-PSCs exhibit a record-high power conversion efficiency of 15.8% with a greatly enhanced J sc of 24.7 mA/cm 2 and a low energy loss of 0.51 eV.

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Obtaining both high open-circuit voltage (Voc) and short-circuit current density (Jsc) has been a major challenge for efficient all-polymer solar cells (all-PSCs). Herein, we developed a polymer acceptor PF5-Y5 with...