Reduced E_loss of Planar-Structured Carbon Counter Electrode-Based CsPbI₃ Solar Cells with Tetrabutylammonium Halide-Modified SnO₂

Cesium lead triiodide (CsPbI3) perovskite with excellent thermal stability owing to its inorganic components has an appropriate band gap and requires no mixed halides for an application in Si tandem solar cells. However, CsPbI3 solar cells have poorer power conversion efficiency (PCE) than organic–inorganic hybrid perovskite solar cells (PSCs) with the same band gap. Tuning electron transport layers (ETL) is an effective method to promote PCE and suppress its hysteresis in PSCs. In this study, the tin dioxide (SnO2) surface was modified with tetrabutylammonium chloride (TBAC), tetrabutylammonium bromide, or tetrabutylammonium iodide. The tetrabutylammonium halogen interlayers increase the conductivity of the SnO2-ETL while lowering the work function, thus making the electron transport more efficient. Moreover, these interlayers alter the SnO2 surface roughness, facilitating high-quality CsPbI3 films with bigger grain sizes and fewer grain boundaries and hence reduced Eloss for PSCs with improved PCE. The optimized carbon counter electrode (CE)-based hole transport layer-free device of fluoride-doped tin oxide/SnO2/TBAC/CsPbI3/C achieves the relatively highest PCE of 12.85%, which is larger than that of pristine PSCs (10.51%) and is also one of the highest efficiencies reported to date for planar-structured CsPbI3 PSCs based on a carbon CE. Our work demonstrates a facile approach of simultaneously optimizing the SnO2-ETL and CsPbI3 film for the construction of efficient carbon CE-based CsPbI3 solar cells.