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

The photovoltage and photocurrent both serve as important design metrics when assessing the performance of photoanodes within photoelectrochemical (PEC) cells. However, to date wide disagreement persists (even in recent literature) 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. Our methodology is based upon directly solving the governing electron and hole continuity equations, coupled self-consistently with Poisson's equation, with appropriate boundary conditions. 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 ...