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. A series of novel non-volatile DTC solid additives with a long flexible alkyl chain were designed and synthesized to improve the efficiency, photostability and mechanical durability of all-polymer solar cells (all-PSCs).