Narrow-Bandgap Semiconductors of Perovskite Rare-Earth Orthoferrites (REFeO3)

Background: Great achievements have been made in improving the power conversion efficiencies of solar cells. However, the price of photovoltaic (PV)-generated electricity still cannot compete with that of conventionally generated power. Thus, novel solar cells made from non-toxic, earth-abundant, and chemically stable materials are desirable to decrease the costs of PV electricity generation. Objective: All-oxide solar cells are a promising next-generation PV technology, fulfilling the requirement of low-cost manufacturing under ambient conditions. This work aims to search for nontoxic, earth-abundant, and chemically stable narrow-bandgap semiconductors for energy applications like all-oxide solar cells. Methods: This work examines a family of perovskite rare-earth (i.e., Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Yb) orthoferrites with XRD analysis, SEM, photoresponse, absorption spectra, Xray photoelectron spectroscopy, fluorescence spectra measured with the laser Raman spectrometer, valence band spectra, the Kelvin probe, the Hall Effect experiment, and theoretical calculation on band structure and the density of states, to screen for the narrow-bandgap semiconductors. Results: The novel Pb-free perovskite narrow-bandgap absorbers, CeFeO3, PrFeO3, TbFeO3, DyFeO3, HoFeO3, and YbFeO3, which are earth-abundant and non-toxic, were screened out potentially for use in all-oxide solar cells or other photovoltaic and optoelectronic applications. Among them, YbFeO3 is approved, having an indirect bandgap of approximately 1.0 eV with a maximum Shockley-Queisser efficiency of 31% for single p-n junction solar cells. Conclusion: The chemically stable, non-toxic, earth-abundant, and narrow-bandgap semiconductors of rare-earth orthoferrites promisingly serve as absorbers, photocatalysts, photoelectrodes, photodetectors, and photoelectronic materials. This work breaks new ground in the search for narrow bandgap all-oxide semiconductors potential for energy applications.