Enhanced device performance and stability of perovskite solar cells with low-temperature ZnO/TiO2 bilayered electron transport layers

Abstract

The instability of perovskite films is a major issue for perovskite solar cells based on ZnO electron transport layers (ETLs). Here, ZnO nanoparticle (NP)- and ZnO sol–gel layers capped with low-temperature processed TiO₂, namely ZnO/TiO₂ bilayered films, have been successfully employed as ETLs in highly efficient MAPbI₃-based perovskite solar cells. It is demonstrated that these ZnO/TiO₂ bilayered ETLs are not only capable of enhancing photovoltaic performance, but also capable of improving device stability. The best device based on the ZnO/TiO₂ bilayered ETL exhibits an efficiency of ∼15% under standard test conditions and can retain nearly 100% of its initial efficiency after 30 days of atmosphere storage, showing much higher device performance and stability compared to those devices based on ZnO single-layer ETLs. Moreover, it is found that perovskite films and devices prepared on the single ZnO sol–gel ETLs are much superior to those deposited on the single ZnO NP-ETLs in both stability and performance, which can be ascribed to fewer surface hydroxyl groups and much smoother surface morphology of the ZnO sol–gel films. The results pave the way for ZnO to be used as an effective ETL of low-temperature processed, efficient and stable PSCs compatible with flexible substrates.