First-principles comparative study of perfect and defective CsPbX3 (X = Br, I) crystals

We thank R. Merkle for numerous fruitful discussions and G. Siegle for experimental assistance. This study was partly supported by the M-ERA-NET project SunToChem (EK). Calculations were performed using computational facilities of St. Petersburg State University and Max Planck Institute for Solid State Research. Open Access funding provided by the Max Planck Society.First principles Density Functional Theory (DFT) hybrid functional PBESOL0 calculations of the atomic and electronic structure of perfect CsPbI3, CsPbBr3 and CsPbCl3 crystals, as well as defective CsPbI3 and CsPbBr3 crystals are performed and discussed. For the perfect structure, decomposition energy into binary compounds (CsX and PbX2) is calculated, and a stability trend of the form CsPbBr3 > CsPbI3 > CsPbCl3 is found. In addition, calculations of the temperature-dependent heat capacity are performed and shown to be in good agreement with experimental data. As far as the defect structure is considered, it is shown that interstitial halide atoms in CsPbBr3 do not tend to form di-halide dumbbells Br2- while such dimers are energetically favoured in CsPbI3, analogous to the well-known H-centers in alkali halides. In the case of CsPbBr3, a loose trimer configuration (Br32-) seems to be energetically preferred. The effects of crystalline symmetry and covalency are discussed, alongside the role of defects in recombination processes.Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²https://pubs.rsc.org/en/content/articlepdf/2020/cp/c9cp06322

First-principles calculations of iodine-related point defects in CsPbI3

Many thanks to A. Lushchik, A. Popov and R. Merkle for numerous fruitful discussions. This study was partly supported by the Latvian Council for Science (grant LZP-2018/1-0147 to EK). R.A.E acknowledges the assistance of the University Computer Center of Saint-Petersburg State University for high-performance computations.We present here first principles hybrid functional calculations of the atomic and electronic structure of several iodine-related point defects in CsPbI3, a material relevant for photovoltaic applications. We show that the presence of neutral interstitial I atoms or electron holes leads to the formation of di-halide dumbbells of I2− (analogous to the well-known situation in alkali halides). Their formation and one-electron energies in the band gap are determined. The formation energy of the Frenkel defect pair (I vacancies and neutral interstitial I atoms) is found to be ∼1 eV, and as such is smaller than the band gap. We conclude that both iodine dumbbells and iodine vacancies could be, in principle, easily produced by interband optical excitation.Latvian Council for Science (grant LZP-2018/1-0147 to EK); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Unravelling the Behavior of Dion-Jacobson Layered Hybrid Perovskites in Humid Environments

Layered hybrid halide perovskites are known to be more environmentally stable than their 3D analogues. The enhanced stability is particularly relevant for Dion-Jacobson-type layered perovskites due to their promising photovoltaic performances. However, in contrast to the expected resilience to moisture, we reveal that the structure of Dion-Jacobson perovskite phases based on a 1,4-phenylenedimethanammonium spacer is disrupted in humid conditions using X-ray diffraction, UV-vis spectroscopy, thermogravimetric analysis, and solid-state NMR spectroscopy. The process takes place at >= 65 +/- 5% relative humidity, with a time scale on the order of minutes. The original layered structure can be restored upon annealing and the hydration can be suppressed by postsynthetic annealing in air, which is attributed to the generation of a self-protective layer of PbI2. This study thereby reveals a unique behavior of layered perovskites in humid environments, which is critical to their stabilizing role in perovskite devices.LRMLP