Chemical Trend of Nonradiative Recombination in Cu(In,Ga)Se2 Alloys

Understanding nonradiative recombination is important for improving semiconductor devices. For Cu(In,Ga)Se${}_{2}$ (CIGS) solar cells, antisite defects have long been considered the main recombination centers, yet the underlying mechanism has remained elusive. Here first-principles calculations show that these ``killer centers'' themselves cannot capture holes efficiently for effective recombination. However, internal conversion to the distorted neutral DX center does open an efficient hole-capture pathway, and DX's stability in CIGS increases with Ga concentration, which resolves the longstanding issue of why the efficiency of CIGS solar cells decreases at high Ga concentration.