A First-Principles Study on the Role of Defects and Impurities in $\beta-In_2S_3$

CdS is a well-established buffer layer for Cu(In, Ga)(S, Se)$_2$ (CIGS)-based thin film solar cells. However, because of its toxicity, low quantum efficiency at blue-wavelength region, and the drawbacks of the chemical bath deposition technique used for its growth, looking for an alternative buffer material has been a matter of debate in recent years. In this context, $\beta-In_2S_3$ is considered as a promising substitution for CdS. $\beta-In_2S_3$ crystallises in an ordered vacancy spinel-like structure, which can accommodate impurities diffusing from the absorber and/or front contact layers. Due to the existence of structural vacancies in its crystalline matrix, the electronic and optical properties of $\beta-In_2S_3$ can be effectively tuned through (un)intentional doping with a third element. In this contribution, we will report on the origin of n-type conductivity of $\beta-In_2S_3$, the influence of Cu and Na incorporation, the thermodynamic stability and electronic properties of $\beta-In_2S_3$, and the influence of O and Cl on electronic properties of $\beta-In_2S_3$