Ab-Initio Exploration of Stoichiometric and Nonstoichiometric CsK ₂ Sb Photocathodes for Photoemission Applications

Bialkali antimonide photocathodes, such as cesium potassium antimonide (CsK2Sb), have emerged as strong candidates for next-generation photocathodes in linear accelerators due to their low work function, fast response, high quantum yield, and visible-light sensitivity. However, a critical gap remains in understanding how defects─unavoidable in real materials and responsible for driving nonstoichiometric phases─affect these desirable photoemissive properties. Most theoretical studies have so far considered only perfectly stoichiometric crystals, overlooking the role of imperfections introduced during synthesis. Here, we address this gap using state-of-the-art first-principles calculations to explore both ideal and defected CsK2Sb. For the stoichiometric phase, our results confirm strong absorption in the visible range and a significantly reduced work function compared to metallic photocathodes, consistent with experiments. Moving beyond the ideal case, we identify cesium and potassium vacancies as the most prevalent intrinsic defects. These vacancies might introduce midgap states, reshape the absorption spectrum, and are poised to strongly influence photoemission efficiency. By connecting intrinsic defects to performance, this work advances fundamental understanding of CsK2Sb and provides practical insights for optimizing high-efficiency photocathodes.