A novel hole extraction layer to enhance the performance of inverted organic solar cells

Abstract

Polyethylenimine ethoxylated (PEIE) is a classical cathode-modifying material. Here, we report the first example of using PEIE as an anode-modifying material. We use MoO₃/PEIE/Ag as a hole extraction layer to enhance the performance of inverted organic solar cells (OSCs). The introduction of an ultrathin PEIE interlayer can markedly reduce the anodic resistance of inverted devices, mostly because the ultrathin PEIE interlayer can separate MoO₃ from Ag, thereby suppressing the reduction of MoO₃ by gaseous Ag to lower-oxidation state Mo species which decrease the work function of MoO₃ and are then detrimental to hole extraction from the photoactive layer. In addition, the PEIE interlayer can act as an optical spacer to optimize the optical absorption of inverted devices. As a result, the novel hole extraction structure of MoO₃/PEIE/Ag increases device efficiency by a factor of 16% relative to conventional MoO₃/Ag in inverted OSCs.