Figure 1. a) The synthetic routes of IC-Br(in) and IC-Br(out). b) Chemical structures of PY-IT, PY-OT and PY-IOT.

Asymmetric acceptor BTP-2F-ThCl-based devices gave the best PCE of 17.06% due to the optimal energy levels relative to those of the devices based on their symmetrical counterparts, BTP-4F (16.37%) and BTP-2ThCl (14.49%).

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.

Both fluorine and ester substituted monothiophene yielded a novel thiophene derivative FE-T. The resulting polymer donor S1 enabled single-junction non-fullerene solar cell with over 16% efficiency.

Power conversion efficiency (PCE) of single-junction polymer solar cells (PSCs) has made a remarkable breakthrough recently. Plenty of work was reported to achieve PCEs higher than 16% derived from the PM6:Y6 binary system. To further increase the PCEs of binary OSCs incorporating small molecular acceptor (SMA) Y6, we substituted PM6 with PM7 due to the deeper highest occupied molecular orbital (HOMO) of PM7. Consequently, the PM7:Y6 has achieved PCEs as high as 17.0% by the hotcast method, due to the improved open-circuit voltage (V OC ). Compared with PM6, the lower HOMO of PM7 increases the gap between E LUMO-donor and E HOMO-acceptor , which is proportional to V OC . This research provides a high PCE for single-junction binary PSCs, which is meaningful for device fabrication related to PM7 and commercialization of PSCs.

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A fullerene additive adjusts the miscibility between donor and acceptor for morphology optimization and reduces bimolecular recombination, assisting significant improvement of fill factor and efficiency.

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