INDIUM DOPED CO₃O₄ FOR ALL-OXIDE PV APPLICATIONS: INSIGHTS FROM COMBINATORIAL EXPERIMENTS AND FIRST PRINCIPLES THEORY

Cobalt oxide, Co₃O₄, is a potential photovoltaics (PV) candidate with optical absorption in the visible region. Additionally, Co₃O₄ exhibits intriguing chemical and catalytic properties. Despite the above range of photon absorption, Co₃O₄ absorbs low energy (< 1.0 eV) photons as well, hence hindering its PV activity. One solution to such photon loss is material doping or alloying, which remains a focal point of oxides research. This could lead to the discovery of efficient PV and photoelectrochemical materials. In the current work we propose Co₃O₄ alloyed with In as a solar photoconversion material (i.e. In@Co₃O₄). Recently, experimentally it was observed that In@Co₃O₄ has enhanced PV activity compared to the parent material, in spite of a marginal change in the band-gap and a decrease in the optical absorption at low levels of alloying. In the present study, we present possible causes for the above anomaly based on density functional theory calculations. In particular, the computed optical absorption spectra, joint density of states, and band structures, show that alloying with In provides a free-electron-like 5s-band in the conduction band, which likely enhances electron mobility and possibly PV activity. However, due to the violation of the transition selection rules, the intensities of the photon absorptions decrease, in agreement with experiment. We envisage that our results will help in the development of novel metal oxide semiconductors.