Utilizing Band Diagrams to Interpret the Photovoltage and Photocurrent in Photoanodes: A Semiclassical Device Modeling Study

Abstract

Photoelectrochemcial (PEC) cells offer a promising route for supplying the world’s population with sufficient energy in an environmentally friendly manner. However, inefficiency remains a major bottleneck towards the large-scale commercialization of PEC cells. The photovoltage and photocurrent serve as important design metrics when assessing the efficiency of photoanodes within PEC cells. However, to date wide disagreement persists regarding how the photovoltage should be physically interpreted; this lack of consensus is further coupled to physical interpretations of the photocurrent. In this work, we utilize state-of-the-art device modeling to help clarify the physical origins of both the photovoltage and photocurrent in photoanodes. Through a systematic examination of a model photoanode (hematite), we correlate directly measurable current-voltage characteristics with operational band diagrams. It is shown that by directly mapping specific operating points of either equal current or equal voltage (both illuminated and in the dark) to band diagram plots, one is able to obtain substantial insights regarding the physical nature of both the photocurrent and photovoltage. By aiding the community wide effort to arrive at a consensus on these concepts, we aim to further enable the design of higher efficiency photoanodes.