Enhanced photostability in polymer solar cells achieved with modified electron transport layer

Photostability of the polymer solar cells (PSCs) remains a challenge to attain, as number of factors including the electron transport layers contribute to the degradation of PSCs when they are tested under 1 sun illumination, along with heat and humidity. Especially electron transport layers (ETLs) have considerable contribution to the overall degradations in these solar cells. Most studied ETL into the fabrication of inverted PSCs is zinc oxide (ZnO) yet the photostability of these PSCs is limited. This degradation most probably occurred due to the direct contact of zinc metal with the photoactive layer. This interface between ZnO and photoactive layer results in the initiation of degradations in PSCs. Keeping in view of this issue, we have modified the ZnO ETL by mixing ZnO nano particles with ethoxylated polyethyleneimine (PEIE) and then passivating this modified ZnO (m-ZnO) with ultrathin PEIE buffer layer. The power conversion efficiency is not affected by this approach, but when PSCs were subjected to 1 sun illumination, these m-ZnO/PEIE based PSCs have shown the enhanced light soaking (LS) stability. These findings indicate that optimizing the interface between the photoactive layer and the electron transport layer can lead to enhanced LS stability.