Highly efficient inverted perovskite solar cells incorporating P3CT-Rb as a hole transport layer to achieve a large open circuit voltage of 1.144 V.

Poly[3-(4-carboxybutyl)thiophene-2,5-diyl] (P3CT) has been noticed as a promising hole transport layer (HTL) for high-performance inverted planar perovskite solar cells (PSCs) due to its excellent stability and relatively high hole mobility. As we all know, the morphology of perovskite films is largely influenced by the substrate materials. Considering the affinity of alkali metal ions Rb and Cs with perovskite materials, inverted perovskite solar cells using alkali metal ion (Rb, Cs) doped P3CT (denoted as P3CT-Rb and P3CT-Cs) as the HTLs were investigated in this work. It turned out that the work function (WF) of P3CT-Rb matches well with the valence band of perovskites. The perovskite (MAPbICl) film deposited on top of the P3CT-Rb film exhibited a dense and uniform morphology with superior crystallinity and few pinholes. Consequently, a high efficiency of 20.52% was achieved for P3CT-Rb HTL-based devices, with an impressive open-circuit voltage (V) of 1.144 V and a high fill factor (FF) of 82.78%.