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...

Efficiency of search of wanted materials with desired properties is limited by the huge search space. By deep learning methods, we demonstrate that space group information can be acquired from band structure inputs to reduce the search space. Despite atomic orbital or accidental degeneracies mixed with lattice degeneracies, band degeneracies as input can yield 96.0% prediction accuracy for cubic systems that leads to a 25.1-fold acceleration of searching speed overall. Additionally, for all space groups, the prediction accuracy is 82.0% with overall 36.9-fold acceleration in the search speed. In addition, valence band degeneracies as inputs can yield satisfactory results and may assist in structural analysis from ARPES results.

Cu2ZnSnS4 (CZTS) is a promising photovoltaic absorber material, however, efficiency is largely hindered by potential fluctuation and a band tailing problem due to the abundance of defect complexes and low formation energy of an intrinsic CuZn defect. Alternatives to CZTS by group I, II, or IV element replacement to circumvent this challenge has grown research interest. In this work, using a hybrid (HSE06) functional, we demonstrated the qualitative similarity of defect thermodynamics and electronic properties in Cu2MgSnS4 (CMTS) to CZTS. We show SnMg to be abundant when in Sn- and Cu-rich condition, which can be detrimental, while defect properties are largely similar to CZTS in Sn- and Cu-poor. Under Sn- and Cu-poor chemical potential, there is a general increase in formation energy in most defects except SnMg, CuMg remains as the main contribution to p-type carriers, and SnMg may be detrimental because of a deep defect level in the mid gap and the possibility of forming defect complex SnMg+MgSn. Vacancy diffusion is studied using generalized gradient approximation, and we find similar vacancy diffusion properties for Cu vacancy and lower diffusion barrier for Mg vacancy, which may reduce possible Cu-Mg disorder in CMTS. These findings further confirm the feasibility of CMTS as an alternative absorber material to CZTS and suggest the possibility for tuning defect properties of CZTS, which is crucial for high photovoltaic performance.