Influence of self-doping on band-edges and Fermi energy of CsPbBr3

Abstract

The electronic properties of CsPbBr 3 thin films cast through a solution route are known to depend on the stoichiometry of the precursors. In this work, with the aid of Kelvin probe force microscopy (KPFM) and scanning tunneling spectroscopy (STS) studies, a complete energy landscape has been derived for the all-inorganic perovskite formed with a wide range of precursor stoichiometries. While the optical band gap of the perovskite is known to remain unchanged with a variation in the stoichiometry, we show the manner in which their Fermi energy, valence band (VB), and conduction band (CB) edges shift. The variation in the energy levels has been correlated to the presence of defects. Since the formation energy of different intrinsic point defects depends on the growth environment, the nature of defects has depended on the precursor stoichiometry used during the formation of the perovskites. The presence of defects has thereby tuned the Fermi energy and the type of electronic conductivity in CsPbBr 3 as well. Here, the CB and VB edges have responded due to the self-doping process. Finally, we have presented the energy landscape of the perovskite with a variation in the precursor stoichiometry, since the energy levels are indeed crucial in designing any optoelectronic devices based on CsPbBr 3 . • Fermi level and band edges of CsPbBr 3 are affected by the precursor stoichiometry. • Energy landscape of the perovskite derived from a combination of KPFM and STS. • CsPbBr 3 formed with CsBr-rich precursors has p -type conductivity. • CsPbBr 3 formed with PbBr 2 -rich growth condition exhibits an n -type behavior. • Bands moved away from vacuum level in perovskites formed in PbBr 2 -rich environment.