Charge Transport Layer-Dependent Electronic Band Bending in Perovskite Solar Cells and Its Correlation to Light-Induced Device Degradation

Perovskite solar cells (PSCs) have achieved power-conversion efficiency of 25.2%; however, their working principle remains under debate, and the stability issue has not been solved. Herein, we reveal that PSCs are governed by a dominant p–n junction occurring at different interfaces depending on the electron-transporting layer (ETL) and that charge accumulation is mainly concentrated at the corresponding dominant junction where degradation is initiated. To confirm this, we investigated the effect of the ETL on the junction, the electric field, and the carrier density in the PCSs using electron-beam-induced current measurement (EBIC) and Kelvin probe force microscopy (KPFM). Also, we analyzed the degradation process of the PSCs working under light illumination in atmosphere, identifying high concentration of single-signed charges at the dominant p–n junction induced degradation. For long-term stability, an ideal p–i–n PSC with less band bending should be designed to prevent charge-driven degradation.