Cationic Vacancies Induced Enhanced Light Absorption with Controlled Leakage Current in Perovskite Ferroelectric Oxides

Visible-light-absorbing ferroelectric perovskite materials have shown promising potential in energy-harvesting applications. However, most of the ferroelectric systems have a large band-gap. The attempts to reduce their band-gap resulted in a large leakage current, which undermines their ferroelectric characteristics. In this study, traditional large-band-gap ferroelectric BaTiO3 (BTO) is modified to show a tunable band-gap capable of visible-light absorption with better leakage current characteristics. This is achieved by incorporating the cationic/anionic vacancies through transition metal Nb and Ni ion substitutions. Here, a comparative study of two BTO-based compositions having differences in the concentration of oxygen and cationic vacancies by varying the donor (Nb)–acceptor (Ni) doping concentration is carried out. Interestingly, the results show that the sample having more cationic vacancy concentration exhibits large band-gap reduction, enhanced light absorption, low leakage current magnitude, better ferroelectric hysteresis loop, and switchable photovoltaic response. Notably, this study unveils that oxygen defects are not a necessary condition for band-gap tuning. Overall, the present work opens a pathway to tune the optical band-gap without deteriorating the ferroelectric properties by controlling donor–acceptor dopant concentration.