A.R. Kirmani, A.E. Mansour, M.I. Saidaminov, X. Cui, D. Shi, A. Alofi, Ya. B. Losovyj, G. Gurung, T.R. Paudel, A.J. Yost, P.A. Dowben, E.Y. Tsymbal, A. Amassian, K. Katsiev
Appl. Phys. Lett., 113, 022101, (2018)
The electronic structure of methylammonium lead bromide (CH3NH3PbBr3) single crystals has been investigated through a combination of resonant photoemission and theoretical modeling. There are Pb spectral contributions throughout the valence band. Importantly, the electronic structure at the top of the valence band is found to be dominated by the hybridized Pb-Br bands, not methylammonium bromide. The results line up with the partial density of states obtained from density functional theory and confirm that much of the valence band has some Pb spectral weight.
The past few years have been witness to a series of major breakthroughs in the field of hybrid organo-lead perovskites, specifically the methyl ammonium lead trihalide perovskites MAPbX3 (MA = CH3NH3, X = Cl, Br, I), as illustrated in Fig. 1. This intense attention is partly the result of better electronic properties exhibited by the single crystal materials, ranging from low defect state densities and long carrier diffusion lengths to high carrier mobilities coupled with the ease of solution processibility. Since the first demonstration of perovskite-based photovoltaics in 2009, highly efficient solar cells have been reported with certified power conversion efficiencies (PCE) breaching 22%. Significant inroads are, as well, being made toward achieving long-term stability. Parallel efforts have been made at demonstrating light emission, photodetection and lasing applications of hybrid perovskites.