Tuning the Photoresponse of CuFeO2 with Mg Doping

Abstract

The influence of semiconductor photoelectrodes’ carrier concentration on their photoresponse is a long hypothesized, but hitherto not quantitatively approached avenue to optimize materials for photoelectrochemical electrode applications. Here, I report tuning of CuFeO\(_{2}\) photoelectrodes using Mg doping to demonstrate the effects of carrier concentration on the photoresponse by combining a variety of solid-state chemistry and photoelectrochemical methods. After synthesizing dense (\(\ge\)85% theoretical), pure, Mg-incorporated pellets (CuFe\(_{1-x}\)Mg\(_{x}\)O\(_{2}\), x = 0, 0.0005, 0.005, 0.02), carrier type and concentrations were quantitatively assessed using the Hall Effect as well as the samples’ resistivities and majority carrier mobility. The same samples were used in a newly designed photoelectrochemical cell to measure their photoresponse. I observe that carrier concentration cannot be independently tuned. In the CuFe\(_{1-x}\)Mg\(_{x}\)O\(_{2}\) system,optimization of the photoresponse by carrier concentration alone is not possible due to coupled electronic effects, changing the nature of the majority carrier type near the saturation limit (x\(\ge\)0.05). To this end, I also explore possible defect chemistries giving rise to varying electronic and photoresponses. I find that the photoresponse is directly correlated to the majority carrier mobility.