This study presents a combined experimental and theoretical study of the electronic structure of two 2D metal halide perovskite films. Ultraviolet and inverse photoemission spectroscopies are performed on solution-processed thin films of the n = 1 layered perovskite butylammonium lead iodide and bromide, BA2PbI4 and BA2PbBr4, characterized by optical absorption and X-ray diffraction, to determine their valence and conduction band densities of states, transport gaps, and exciton binding energies. The electron spectroscopy results are compared with the densities of states determined by density functional theory calculations. The remarkable agreement between experiment and calculation enables a detailed identification and analysis of the organic and inorganic contributions to the valence and conduction bands of these two hybrid perovskites. The electron affinity and ionization energies are found to be 3.1 and 5.8 eV for BA2PbI4, and 3.1 and 6.5 eV for BA2PbBr4. The exciton binding energies are estimated to be 260 and 300 meV for the two materials, respectively. The 2D lead iodide and bromide perovskites exhibit significantly less band dispersion and a larger density of states at the band edges than the 3D analogs. The effects of using various organic ligands are also discussed.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: Work at Princeton was supported in part by a grant from the US-Israel Binational Science Foundation (Grant # 2014357) and by a grant from the Princeton Environmental Institute and Andlinger Center. Work at the Georgia Institute of Technology was supported in part by the Georgia Research Alliance and ONR under Award No. N00014-17-1-2208. Work at King Abdullah University of Science and Technology was supported by KAUST Supercomputing Laboratory. Fruitful discussions with Prof. Omer Yaffe are gratefully acknowledged.