A Combined Theoretical and Experimental View on Valence and Conduction Band Densities of States of Lead Halide Perovskites

We present results for the valence and conduction band density of states (DOS), measured via ultraviolet and inverse photoemission spectroscopies for three lead halide perovskites. Specifically, the DOS of MAPbI$_3$, MAPbBr$_3$, and CsPbBr$_3$, grown on different substrates, are compared. Theoretical DOS, calculated via hybrid density functional theory and including spin-orbit coupling, are compared to experimental data. The agreement between experiment and theory, obtained after correcting the latter for quantitative discrepancies, leads to the identification of valence and conduction band spectral features. In particular, this comparison allows for precise determination of the energy position of the band edges, namely ionization energies and electron affinities of these materials. We find an unusually low DOS at the valence band maximum (VBM) of these systems, which confirms and generalizes previous findings of strong band dispersion and low DOS at the VBM of MAPbI$_3$. This calls for special attention when using electron spectroscopy to determine the frontier electronic states of lead halide perovskites. [1] Endres et al., J. Phys. Chem. Lett. 7, 2729 (2016)