Dynamic Photoelectrochemical Device with Open-Circuit Potential Insensitive to Thermodynamic Voltage Loss

The open-circuit potential ( V_oc) represents the maximum thermodynamic potential in a device, and achieving a high V_oc is crucial for self-biased photoelectrochemical (PEC) devices that use only solar energy to produce chemical energy. In general, V_oc is limited by the photovoltage ( V_ph), which is a potential difference generated by light-induced thermodynamic processes at semiconductor photoelectrodes, such as the generation and recombination of charge carriers. Therefore, low light intensity and nanostructured semiconductor materials degrade V_ph (and V_oc) by inefficient carrier generation and by enhancing recombination loss, respectively. Here, we report that V_oc in dynamic PEC devices employing a porous NiO _x/Si photocathode is insensitive to thermodynamic losses, which was clarified by varying the carrier generation and recombination rates. The V_oc values were observed to be unchanged even under a low light intensity of 0.1 sun, as well as for different morphologies such as nanostructured and polycrystalline Si. These findings shed light on the potential merit of dynamically operated PEC systems.