Alloying ZnS to create transparent conducting materials

In the exploration and design of new transparent conducting materials (TCM), alloyed ZnS has shown great promise. Particularly, Cu:ZnS is particularly intriguing as a p-type TCM, which, when combined with n-doped ZnS, could find eventual applications in photovoltaics and optoelectronics. We desire to identify the most promising materials with the optimal combination of physical stability, transparency, and electrical conductivity. In this study, we employ hybrid density functional theory and a new carrier transport model, aMoBT, developed within the Boltzmann transport framework, to analyze the defect physics of different cation and anion alloyed ZnS. We obtain formation energies and correct band gaps for ZnS doped with B, Al, Ga, In, Tl, F, Cl, Br and I. Furthermore, we calculate the effective mass and electrical mobility of these compounds at various compositions, temperatures and electron concentrations, to identify the best-performing n-doped ZnS TCMs, without need for costly experimental trial and error. Our results show that among the doping candidates, Al:ZnS is the most promising with the highest solubility, the smallest reduction in the band gap, and the highest conductivity of 41 S · cm^-1 at 300 K (9.375% Al, n = 2.32 × 10¹⁸ cm^-3). Our calculations predict that the conductivity may be as high as 881 S · cm^-1 (at 300 K) at a high concentration of n = 1.00×1020 cm^-3. Furthermore, our ab initio electronic and thermodynamics calculations provide significant insight on phase stability and the underlying electronic interactions that result in optimal transparent conducting behavior.