Defect calculations using a combined SCAN and hybrid functional in γ-CsPbI₃

Abstract

γ-CsPbI3 solar cells have achieved promising efficiencies, yet the quantitative understanding of their defect properties is limited due to severe computational challenges of hybrid functionals. We have discovered an algorithm...

Surface Purification and Compensation of I Interstitial in Quasi-2D CsPbI3

“…Therefore, the I int 2D and I int bulk show different stabilities in the 1− state. Similar to the bulk results of the γ-phase, 12 we find a reconstruction surrounding the I int in the bulk results of the α-phase. Then, we conduct a calculation of the partial charge density contour and find that there also exists an enhanced bond orbital coupling around the reconstruction area that stabilizes the 1− state of I int bulk .…”

“…When calculating the defect formation energy and defect transition levels, a combined meta-generalized-gradient approximation and hybrid functional ,, with spin–orbit coupling is used. The defect formation energy as a function of Fermi energy is defined as normalΔ H f ( D , q ) = E D ( q ) − E normalh normalo normals normalt + ∑ i [ n i false( E i + μ i false) ] + q ( E normalF + ∈ V B M ) where E D ( q ) and E host are the energy of defective cells at charge state q and host cells, respectively; n i , E i , and μ i represent the number changes, atomic energy, and chemical potential of element i , respectively; E F and ϵ VBM are the Fermi energy and absolute position of the valence band maximum (VBM), respectively.…”

“…When calculating the defect formation energy and defect transition levels, a combined meta-generalized-gradient approximation and hybrid functional 12,47,48 with spin−orbit coupling is used. The defect formation energy as a function of Fermi energy is defined as…”

“…According to the bulk results, I int has relatively low defect formation energy under I-rich conditions with deep transition levels and a bipolar nature. 12 Therefore, it can be one of the most abundant nonradiative recombination centers in the crystal. In addition, Evarestov et al demonstrate an easy formation of I vacancy-interstitial Frenkel pairs.…”

“…Experimentally, during typical CsPbI 3 synthesis using an antisolvent reprecipitation method, many I vacancies are generated on the crystal surface − due to their low defect formation energies. − They induce undesirable ion diffusion channels and cause crystal degradations. − To avoid this problem, one of the solutions is introducing surfactants to slow the detrimental interlayer diffusion of the atoms. For example, amines, carboxylic acid, and rare-earth metal can stabilize crystal surfaces and block the diffusion channels of I vacancies that lead to phase segregation in CsPbI 3 . − However, these surfactants may dissociate or decompose during the annealing process, still rendering a limited device performance.…”