Enhancement of Electron Transport Properties for Highly Efficient Inverted Organic Solar Cells

Abstract

Zinc oxide (ZnO) derived by the sol-gel method is widely studied as electron transport layers (ETLs) for inverted organic solar cells (OSCs) owing to its high transparency, proper energy level, and good stability. However, the currently applied high-temperature-processed ZnO ETL is not suitable for flexible OSCs. Furthermore, low-temperature-processed ZnO has poor crystallinity and many defects inside, which leads to low electron mobility and limits the power conversion efficiency (PCE). In this work, we applied aluminum-doped ZnO (AZO) and a suitable annealing process to passivate defect sites and optimize the surface morphology. By using AZO as ETL in inverted OSCs with the PM6:DTY6 system, the maximum PCE is up to 16.0% on rigid and 14.4% on flexible device, which is a result of the high current density compared with the ZnO. These properties also improved ETL thickness tolerance, maintaining a PCE >15% even as the AZO ETL thickness increases to 190nm. In conclusion, AZO could be promising ETL for efficient OSCs, which paves the avenue for the following commercialization process.