Effect of vacancy defects on photoelectric properties of K2CsSb photocathode

Abstract

A variety of different vacancy defect compounds may be formed during the preparation of the K2CsSb photocathode. To better understand the action mechanism of vacancy defects, the influence of Cs vacancy, K vacancy, Sb vacancy, Cs-K vacancy, Cs-Sb vacancy, K-Sb vacancy on the electronic structures and optical properties of K-Cs-Sb cathodes were investigated by the first-principles method based on density functional theory. The band structures show that, K-Cs-Sb cathode materials with Sb vacancy, Cs-Sb vacancy, K-Sb vacancy, adjacent K double vacancies are indirect bandgap semiconductors, other models are all direct bandgap semiconductors. Besides, the Sb vacancy-contained models exhibit n-type semiconductor property, while other models with only K or Cs vacancy all exhibit p-type semiconductor property. The calculated results about formation energy and formation enthalpy indicate that the Cs vacancy defects are easier to form and more thermodynamically stable than other vacancy defects. In terms of optical properties, in the energy range of 2.4–3.2 eV produced by neutrino scintillator radiation, K2CsSb without vacancy defects possesses the maximum absorption coefficient. The Sb vacancy-contained defects cause the absorption coefficient peak to shift to the lower energy position, while other vacancy defects without Sb vacancies are just the opposite.