Abstract
The description of the band gap of halide perovskites at the level of density functional theory (DFT) has been subject of several studies but still presents significant problems and deviations from experimental values. Various approaches have been proposed, including the use of system-specific hybrid functionals with a variable amount of exact exchange or the explicit inclusion of spin–orbit coupling (SOC) effects. In this work, we present a pragmatic recipe to compute the band gap of halide perovskites with a minimum average error. The recipe is tested on a set of 36 halide perovskites of the type ABX3 [A = Cs, methyl-ammonium (MA), and formamidinium (FA); B = Ge, Sn, and Pb; and X = Cl, Br, and I] for which experimental estimates of the band gap have been reported in the literature. Upon assessment of the accuracy of commonly used DFT functionals and the analysis of their performances based on error and statistical analysis, we suggest a strategy to compute band gaps in halide perovskites with a single functional. This is based on the use of the hybrid HSE06 functional where SOC is included exclusively for Pb-containing compounds. The results are rationalized in terms of the materials’ chemical nature and are corroborated by the prediction of their expected efficiencies in solar cells. The calculated efficiencies from band gaps obtained with the proposed approach closely follow the experimental trend, demonstrating the importance of adopting a reliable but material-independent computational strategy to screen new halide perovskite materials for solar energy conversion.
Highlights
The development of efficient devices capable of converting solar light into electrical or chemical energy in an efficient way is essential for the future of the energy transition
Starting from the pioneering work by Fujishima and Honda who demonstrated that a stable, cheap, and abundant material such as TiO2 is active for the photocatalytic water splitting,[1] a lot of efforts have been devoted to the development of new materials for application in solar cells, photocatalysis, and environmental remediation.[2−6] Despite these efforts, very often single-phase materials display low efficiencies due to two detrimental events
We proposed a simple recipe to evaluate the band gap of halide perovskites within the density functional theory (DFT) approach
Summary
The development of efficient devices capable of converting solar light into electrical or chemical energy in an efficient way is essential for the future of the energy transition. We propose a simple recipe for the calculation of the band gap of halide perovskites using a single DFT approach which results in an average accuracy in band gap prediction of 0.3 eV, which corresponds to an improvement of 0.2 eV compared to other commonly used approaches, and in a smaller standard deviation To this end, we investigated at the DFT level, the entire set of perovskites of type ABX3 (A = Cs, MA, or FA; B = Ge, Sn, or Pb; and X = Cl, Br, or I) for which both crystal structure and band gap are experimentally available. Conclusions and future perspectives are summarized in the last section
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