Photoreflectance and Photoluminescence Study of Antimony Selenide Crystals

Among inorganic, Earth-abundant, and low-toxicity photovoltaic technologies, Sb2Se3 has emerged as a strong material contender reaching over 10% solar cell power conversion efficiency. Nevertheless, the bottleneck of this technology is the high deficit of open-circuit voltage (VOC) as seen in many other emerging chalcogenide technologies. Commonly, the loss of VOC is related to the nonradiative carrier recombination through defects, but other material characteristics can also limit the achievable VOC. It has been reported that in isostructural compound Sb2S3, self-trapped excitons are readily formed leading to 0.6 eV Stokes redshift in photoluminescence (PL) and therefore significantly reducing the obtainable VOC. However, whether Sb2Se3 has the same limitations has not yet been examined. In this work, we aim to identify main radiative carrier recombination mechanisms in Sb2Se3 single crystals and estimate if there is a fundamental limit for obtainable VOC. Optical transitions in Sb2Se3 were studied by means of photoreflectance and PL spectroscopy. Temperature, excitation intensity, and polarization-dependent optical characteristics were measured and analyzed. We found that at low temperature, three distinct radiative recombination mechanisms were present and were strongly influenced by the impurities. The most intensive PL emissions were located near the band edge. In conclusion, no evidence of emission from self-trapped excitons or band-tails was observed, suggesting that there is no fundamental limitation to achieve high VOC, which is very important for further development of Sb2Se3-based solar cells.