Efficiency enhancement of dopant-free perovskite solar cells by employing fluoro-substituted electron donor-electron acceptor type polymeric hole-transporting materials

For the conventional n-i-p perovskite solar cells (PVSCs), dopant-free hole-transporting polymers can be employed to achieve high device performances. Herein, two electron donor-electron acceptor (D-A) type conjugated polymers PBCz-BTz and PBCz-FBTz were developed, in which benzodithiophene served as the D unit, and benzotriazole without or with fluoro-substituents was used as the A unit. PBCz-FBTz with fluoro-substituents exhibits a better pi-pi stacking effect, suitable energy levels, higher backbone planarity and hole mobility to PBCz-BTz. Thus, the champion device based on PBCz-FBTz exhibits an outstanding power conversion efficiency of 20.71% and retains over 90% of its original PCE after being stored under ambient conditions for 30 days. Our work confirms that developing novel polymeric HTMs with fluoro-substituents is a promising molecular design strategy for highly efficient PVSCs. PBCz-FBTz with fluoro-substituents exhibits superior hole transport properties and passivation effects to PBCz-BTz. The devices employing PBCz-FBTz as dopant-free hole-transporting material show a champion PCE of 20.71% with excellent stability.