Polaron-induced efficiency limitations of solar H2O splitting by BiVO4

In this paper, we present a theoretical study of atomistic mechanisms of polaron formation in BiVO4 and its impact on solar-to-hydrogen (STH) conversion efficiency. We simulated polaron formation, calculated the energies of polaron states, and computed the frequency-dependent dielectric function using first-principles density functional theory and density functional perturbation theory, both with the Hubbard U correction. The results indicate the formation of electron polarons at vanadium sites and hole polarons at oxygen sites. The calculated energies of polaronic states result in the values of photovoltage of ∼0.53 and ∼1.16 eV for electron and hole polarons, respectively. These photovoltage results are not only lower than the estimated optical gap of 2.40 eV but also smaller than the minimum potential energy required for water splitting (2.00 eV), indicating that polaron formation limits the photovoltage. Furthermore, the computed dielectric function revealed changes in both the optical and static dielectric constants due to polaron formation. These changes correlate closely with the total dielectric constant, which influences the effective potential well as well as the maximum polaron binding energy and, consequently, the polaron mobility.