Role of Electron- and Hole-Collecting Buffer Layers on the Stability of Inverted Polymer: Fullerene Photovoltaic Devices

Systematic device performance and air stability comparison of inverted architecture polythiophene:fullerene photovoltaic cells with eight different electron-collecting layers (ECLs) and two hole-collecting layers are presented in this study. Regardless of the ECL, we achieved an efficiency of over 3.5% and lifetime of over 1000 h. These results indicate the relative interchangeability of various solution-processed ECLs. Long-term (>5000 h) air exposure revealed a secondary failure mechanism of inverted cells, which is assigned to hindered exciton harvesting. Notably, devices with a polymeric hole-collecting layer and Ag/Al electrode exhibited the longest lifetime (defined as 80% of the initial performance) of 4000 h, compared with 3000 h for MoO 3/Ag/Al.