Iridium-Doping as a Strategy to Realize Visible-Light Absorption and p-Type Behavior in BaTiO₃

BaTiO3 (BTO) typically demonstrates a strongn-typecharacter with absorption only in the ultraviolet (lambda <= 390 nm) region. Extending the applications of BTO to a range of fieldsnecessitates a thorough insight into how to tune its carrier concentrationand extend the optical response. Despite significant progress, simultaneouslyinducing visible-light absorption with a controlled carrier concentrationvia doping remains challenging. In this work, a p-type BTO with visible-light(lambda <= 600 nm) absorption is realized via iridium (Ir)doping. Detailed analysis using advanced spectroscopy/microscopy toolsrevealed mechanistic insights into the n- to p-type transition. Thecomputational electronic structure analysis further corroborated thisobservation. This complementary data helped establish a correlationbetween the occupancy and the position of the dopant in the band gapwith the carrier concentration. A decrease in the Ti3+ donor-levelconcentration and the mutually correlated oxygen vacancies upon Irdoping is attributed to the p-type behavior. Due to the formationof Ir3+/Ir4+ in-gap energy levels within theforbidden region, the optical transition can be elicited from or tosuch levels, resulting in visible-light absorption. This newly developedIr-doped BTO is a promising semiconductor with imminent applicationsin solar fuel generation and optoelectronics.