Multifunctional solid additive enables all-polymer solar cells with improved efficiency, photostability and mechanical durability

All-polymer solar cells (all-PSCs) have recently made remarkable progress owing to the emergence of polymerized small molecule acceptors. However, the fabrication of all-PSCs featuring high efficiency, desirable photostability and excellent mechanical durability remains challenging. Herein, we designed and synthesized a series of novel non-volatile solid additives, namely DTC-Cn (n is 8, 12 and 16) with a long flexible alkyl chain. It was discovered that the molecular miscibility and phase-separated morphology of PM6 : PY-C11 blend can be finely tuned by introducing DTC additives with different alkyl chain lengths. As a result, the DTC-C12-processed all-PSC produces a maximum efficiency of 18.35% (certified as 17.9%), which is among the highest efficiencies reported for the binary all-PSCs so far. The general applicability of DTC-C12 is further confirmed by using two other all-polymer systems, and the corresponding devices all yield enhanced efficiency. In addition, DTC-C12 can effectively suppress molecular aggregation and material decomposition caused by continuous illumination, which results in superior device photostability (a T₈₀ lifetime of 1120 h). More importantly, the mechanical robustness of the flexible device is also improved with the addition of DTC-C12. This work demonstrates the great potential of utilising non-volatile solid additives with a flexible alkyl main chain to boost the comprehensive performance of all-PSCs.