First-Principle Study of the Electronic Structure and Stability of Reconstructed AgInSe2 (112) Polar Surfaces

Chalcopyrite AgInSe
₂
(AIS) is a candidate material for alloying with Cu(In,Ga)Se
₂
(CIGS) to increase the band gap and potentially enhance the efficiency of CIGS thin-film photovoltaic materials. As Cu depletion at the heterojunction of CIGS photovoltaic cells plays an important role in its high efficiency, the stoichiometry, stability, and electronic structure of AIS surfaces are a matter of interest. In this work, hybrid density functional theory was implemented to study the (112) polar surface of AIS. We found that, similar to the corresponding CIS surface, as-cleaved AIS (112) surfaces are reconstructed by Ag vacancies or Ag-on-In antisites depending on the thermodynamic environment. The former is found to be more favorable under most typical growth conditions. Moreover, unlike CIS, the fluctuations in the position of the AIS valence band are small for the Ag vacancy reconstruction, but can increase if antisite reconstructions are present. Simulated scanning tunneling microscopy topographs are compared to those obtained from the experiment. Our findings suggest that alloying Ag into CIGS can potentially reduce electron-hole recombination at defects, leading to improved device performance.