Band offset studies in MAPbI3 perovskite solar cells using X-ray photoelectron spectroscopy

The absolute band edge positions have significant impact on carrier transport in materials and solar cells. In the present work, an attempt has been made to examine the interfaces of different layers and to obtain band offsets, in one and two step deposited MAPbI₃ peroviskite solar cells (PSC), employing X-ray photon spectroscopy (XPS). The values of conduction band offset (CBO) at TiO₂/MAPbI₃ and the valance band offset (VBO) at MAPbI₃/Spiro-MeOTAD were 0.27eV and 0.26 eV, respectively. Relatively high VBO (0.29 eV) at MAPbI₃/Spiro-MeOTAD interface in two-step PSC as compared to that of one step PSC (0.26 V) caused a barrier for hole transfer at the interface and hence results a 2% fall in its photo conversion efficiency (PCE). Surface roughness analysis using atomic force microscopy revealed a relatively smooth surface for one step method resulting in a reduction of interface resistance leading to a better charge transport and improved PCE.