Hole-transporting layer based on a conjugated polyelectrolyte with organic cations enables efficient inverted perovskite solar cells

Conjugated polyelectrolytes (CPEs) have been successfully applied in organic photovoltaics and organic light-emitting diodes, and recently those with inorganic cations became to serve as a hole-transporting layer (HTL) in inverted perovskite solar cells (iPSCs), whereas the CPE HTL materials with organic cations are really limited. In this work, we design a CPE whose side-chains are end-capped by CH3NH3+ cations, the same cations as that in the perovskite layer. The CPE is found to be more compatible to the perovskite material, and shows stronger abilities to reduce the traps both at the surface and in the bulk of the perovskite layer, compared with the typical poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS). The resulting iPSC presents much improved photovoltaic properties and a better long-term stability, with a power conversion efficiency of 19.76%, which is the highest value ever reported for iPSCs based on CPE HTLs.