Charge Carrier Dynamics in Electron-Transport-Layer-Free Perovskite Solar Cells

Better understanding of the carrier dynamics process in electron-transport-layer (ETL)-free perovskite solar cells (PSCs) enables further exploration of the perovskite potential and corresponding device structure design. Herein, an ETL-free perovskite/transparent conductive film SnO2:F(FTO) contact with different perovskite thicknesses illuminated by varied light intensities were investigated by scanning probe microscopy technology. Strong charge transfer occurs at the perovskite/FTO contact, evidenced by the variations of both the surface contact potential and local current value. Mott–Schottky analysis based on capacitance–voltage measurements suggests that the interface property of the perovskite/FTO contact is similar to that of the perovskite/TiO2/FTO structure, making it ideal for fabricating ETL-free PSCs. The cross-sectional surface potential drop was found to be mainly located at the CH3NH3PbI3/FTO heterojunction, suggesting a single diode junction in the ETL-free PSCs. Furthermore, a single-side abrupt p–n++ junction model is employed to illustrate the energy level alignment at the perovskite/FTO contact. This study will be helpful for understanding the carrier dynamics process and thus achieving high device efficiency in the ETL-free PSCs.