Effect of nitrogen annealing on the optoelectronic properties of manganese vanadate

Abstract

Semiconducting oxides are often stable, non-toxic, and can potentially be deposited at a low cost. The existence of oxides with appropriate bandgap (<1.8 eV) and reasonable mobility points towards the alluring possibility of employing oxides as absorbers in ‘all-oxide’ solar cells. However, oxide absorbers have remained elusive due to the debilitating effects of low mobility, deep-defects, and inefficient doping, which degrade their optoelectronic performance. In this work, we report the effects of annealing on the optoelectronic properties of an emerging oxide solar absorber, manganese vanadate (Mn2V2O7, MVO). Films deposited using pulsed laser deposition show no photoluminescence (PL). After annealing in a nitrogen ambience, sharp PL (FWHM ∼ 100 µeV) peaks are observed at low temperatures, which indicates improved optoelectronic quality. Our analysis suggests these emissions are from carriers trapped in very shallow native acceptor and donor type defects. This improvement is correlated with the reduction in Urbach energy, which also suggests reduced electronic disorder. Coupled with low bandgap and easy processing, MVO seems to be an exciting material for optoelectronics and photovoltaics.