Atomic ordering effects on (LaCrO3)n/(LaFeO3)n perovskite superlattices for solar absorption

Due to the ever-increasing energy demand and heavy dependence on non-renewable resources, the search for an economically competitive renewable energy resource is at an all-time high. Among the identi ed renewable energy resources, sunlight is the most available, however, the conversion to electricity is largely determined by the absorbent layer of a solar cell, often reaching only 15% effciency in commercial applications. Consequently, it is necessary to develop novel materials to enhance said absorbing layer. Oxide heterostructures present themselves as an alternative as they allow for chemical doping, which can lead to higher efficiency due to optical band gaps in the optimally efficient range, band-gap graded materials, and an internal potential gradient for charge carrier separation. Perovskite oxide superlattices of LaCrO3 and LaFeO3 have shown varying magnetic, electronic, and optical properties through atomic ordering. This presents the interesting possibility to tune properties based purely on the local chemical environment. Recently, a (LaCrO3)1/(LaFeO3)1 rock-salt ordered superlattice has shown an anomalous optical band gap of 1.6 eV, 1 eV below that of either parent compound, making it suitable for solar applications. Density functional theory is used to investigate the e ect of artificial atomic ordering and superlattice periodicity in layered and rock-salt con gurations on the optical band gap. Two conclusions are drawn from this study. First, rock-salt ordering is predicted to reduce the optical band gap following Hunds rules and the Goodenough Kanamori rules for superexchange interactions with a ferrimagnetic spin ordering, resulting in a net magnetization of 2 , which is not observed in either bulk compound. Second, the variation in superlattice periodicity, specifically a (LaCrO3)2/(LaFeO3)2 structure, lifts inversion symmetry and leads to a spontaneous electric polarization of 0.0280 C/cm2, possibly increasing optical absorption efficiency through increased charge carrier separation.%%%%M.S., Materials Science and Engineering  – Drexel University, 2014