High‐Efficiency Perovskite Solar Cell Based on Poly(3‐Hexylthiophene): Influence of Molecular Weight and Mesoscopic Scaffold Layer

Abstract Here, we investigated the effect of the molecular weight (MW) of poly 3‐hexylthiophene (P3HT) hole‐transport material on the performance of perovskite solar cells (PSCs). We found that by increasing the MW the photovoltaic performances of the cells are enhanced leading to an improvement of the overall efficiency. P3HT‐based PSCs with a MW of 124 kDa can achieve an overall average efficiency of 16.2 %, double with respect to the ones with a MW of 44 kDa. Opposite to spiro‐OMeTAD‐based PSCs, the photovoltaic parameters of the P3HT‐based devices are enhanced by increasing the mesoporous TiO 2 layer thickness from 250 to 500 nm. Moreover, for a titania scaffold layer thickness of 500 nm, the efficiency of P3HT‐based PSCs with high MW is larger than the spiro‐OMeTAD based PSCs with the same scaffold layer thickness. Recombination reactions of the devices were also investigated by voltage decay and electrochemical impedance spectroscopy. We found that the relationship between P3HT MW and cell performance is related to the reduction of charge recombination and to the increase of the P3HT light absorption by increasing the MW.