Enhanced p-type dopability of P and As in CdTe using non-equilibrium thermal processing

One of the main limiting factors in CdTe solar cells is its low p-type dopability and, consequently, low open-circuit voltage (VOC). We have systematically studied P and As doping in CdTe with first-principles calculations in order to understand how to increase the hole density. We find that both P and As p-type doping are self-compensated by the formation of AX centers. More importantly, we find that although high-temperature growth is beneficial to obtain high hole density, rapid cooling is necessary to sustain the hole density and to lower the Fermi level close to the valence band maximum (VBM) at room temperature. Thermodynamic simulations suggest that by cooling CdTe from a high growth temperature to room temperature under Te-poor conditions and choosing an optimal dopant concentration of about 1018/cm3, P and As doping can reach a hole density above 1017/cm3 at room temperature and lower the Fermi level to within ∼0.1 eV above the VBM. These results suggest a promising pathway to improve the VOC and efficiency of CdTe solar cells.