Electron-Hybridization-Induced Enhancement of Photoactivity in Indium-Doped Co₃O₄

We investigate the significance of indium (In) doping of Co₃O₄ in the operation of TiO₂|Co-In-O|RuO₂ all-oxide solar cells by employing combinatorial experiments and density functional theory (DFT) calculations. We observed an increase in the open-circuit voltage, V_oc, of more than 240 mV with an enhancement by a factor of 4 in the short-circuit current, J_sc, in the low-doping range. This constitutes a maximum power that is five times greater than that of pure Co₃O₄-based photovoltaic (PV) devices. Surprisingly, a concurrent marginal change in the band gap and a decrease in the optical absorption coefficient as a function of indium concentration was observed, contrary to what has been assumed previously. Using DFT in conjunction with joint density of states calculations, we show that with increasing amounts of In, there is a reduction in the low-energy photon absorption due to disallowed electronic transitions. Moreover, we show that emergence of In 5s states results in a free-electron-like band in the conduction band. We propose that this might reduce the rate of carrier recombination (reflected in higher open-circuit voltage) and enhance the electron diffusion lengths (reflected in higher short-circuit current), leading to improved PV activity. We expect that our results will advance the understanding and development of novel metal oxide semiconductors for low-cost PV applications. (Graph Presented).