Abstract
Perovskite compounds show promise for charge generation in solar cells because of their high density of excitons when exposed to light. New experiments reveal the origin of this behavior, which could point the way to more efficient optoelectronic devices.
Highlights
In recent years, perovskites have been identified as good candidate materials for inexpensive, high-efficiency photovoltaic devices [1,2,3,4,5,6,7,8,9,10,11]
We find that the ground-state electronic structures of both MAPbI3 and FA0.85Cs0.15PbI2.9Br0.1 systems are quite similar and the band-structure calculations may help to identify optical transitions in general, the ground-state calculations do not contain the most important information, i.e., excitons and electronic correlations
The accurate Bethe-Salpeter equation (BSE) calculations of both the first interband transition at the Γ point and the low-energy exciton peak with experimental data show that the interplay of strong electron-electron and electron-hole interactions determines fundamental properties, yielding high-density excitons in the formamidinium lead halide perovskites
Summary
Perovskites have been identified as good candidate materials for inexpensive, high-efficiency photovoltaic devices [1,2,3,4,5,6,7,8,9,10,11]. Other perovskites have been developed for efficient solar cells wherein the MA cations have been replaced These include the inorganic cesium lead halides (CsPbX3) [15,16] and formamidinium lead halides, HCðNH2Þ2PbX3 (FAPbX3) [7,8,9]. While single-crystal measurements may be useful for the determination of electrical and optical properties at room temperature, at lower temperatures, nanocrystalline effects become important. In this investigation, we intentionally use thin nanocrystalline films. This is the first temperaturedependent spectroscopic ellipsometry study on Pb-based perovskites, and from these measurements, we are able, for the first time, to determine the cause of the unusual behavior of the excitons at different temperatures
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