Constructing the Electronic Structure of CH₃NH₃PbI₃ and CH₃NH₃PbBr₃ Perovskite Thin Films from Single-Crystal Band Structure Measurements

Abstract

Photovoltaic cells based on halide perovskites and possessing remarkably high power conversion efficiencies have been reported. To push the development of such devices further, a comprehensive and reliable understanding of their electronic properties is essential, but presently not available. To provide a solid foundation for understanding the electronic properties of polycrystalline thin films, we employ single crystal band structure data from angle-resolved photoemission measurements. For two prototypical perovskites (CH3NH3PbBr3 and CH3NH3PbI3) we reveal the band dispersion in two high symmetry directions, and identify the global valence band maxima. With these benchmark data, we construct "standard" photoemission spectra from polycrystalline thin film samples and resolve challenges discussed in the literature of determining the valence band onset with high reliability. Within the framework laid out here, the consistency of relating the energy level alignment in perovskite-based photovoltaic and optoelectronic devices with their functional parameters is substantially enhanced.

Photoelectron spectroscopy on single crystals of organic semiconductors: experimental electronic band structure for optoelectronic properties

“…Despite such difficulties, several research groups have challenged the ARUPS measurements on the single crystal halide perovskites. [196][197][198][199][200] We herein digest the cases of the single crystal methylammonium lead triiodide (CH 3 NH 3 PbI 3 ; MAPI). † † † Lee et al reported the ARUPS results on MAPI single crystal samples obtained under various excitation photon energies in a range of 74-200 eV.…”

“…209 Afterward, Zu et al also demonstrated the ARUPS analyses on the single crystal MAPI. 200 Their experimental conditions were similar to those of Yang et al; 199 an only apparent difference is that they cleaved the MAPI single crystal surface in a N 2 -filled glovebox, instead of in air, and the ARUPS measurements were conducted on the samples without air exposure. In this work, the ARUPS results taken along the G-% X and G-% M directions were interpreted to mainly represent the valence band dispersion in the X-M and X-R directions, respectively, as shown in Fig.…”

Gap States in Methylammonium Lead Halides: The Link to Dimethylsulfoxide?

“…Photoemission spectroscopy typically generates non-equilibrium conditions with some degree of SPV and band flattening at semiconductor surfaces, on MHP surfaces in particular. [31][32][33] This circumstance places some uncertainty on the equilibrium surface position of E F measured via UPS. To sort out this issue in the present case, we performed KP-CPD/SPV measurements on all the films, in the dark and under controlled white light intensity.…”

Progress of Surface Science Studies on ABX3‐Based Metal Halide Perovskite Solar Cells

“…This study highlights the necessity to use a logarithmic intensity scale to determine the VBM onset (with a remaining fundamental uncertainty of ≈50 meV, mostly underestimating the onset) 49b,c,52. On a separate note, ARPES allows the evaluation of the hole effective mass ( m h *) by performing a parabolic fit of the VBM at points R and M 49i,52,54. Values of 0.18 ± 0.06 m 0 at M (along X–M) and 0.50 ± 0.10 m 0 near R (along X–R).…”

“…The photoemission intensities are displayed in linear and logarithmic scales to highlight the variations in the onset of VBM determination. Reproduced with permission . Copyright 2019, American Chemical Society.…”