Tuning photoelectrochemical performance of poly(3-hexylthiophene) electrodes via surface structuring

Abstract

Organic semiconductors are gaining increasing attention as promising active materials in aqueous electrochemical and photoelectrochemical applications. Controlling the semiconductor/electrolyte interface is a critical aspect. The aim of this work is to increase the electrochemical surface area of an archetypical polymeric semiconductor, poly(3-hexylthiophene), P3HT. Here we use a technique of blending with polystyrene, phase separation, followed by selective removal of polystyrene to obtain various nano/microstructures of P3HT. We evaluate how three-dimensional structuring of P3HT affects electrochemical capacitance, photovoltage generation, and photoelectrochemical currents. The aqueous wettability of the exposed surface is critical, and it can be significantly modified by employing oxygen plasma treatment. Structured and plasma-hydrophilized P3HT samples demonstrate higher photoelectrochemical currents for the oxygen reduction reaction. We find that regardless of structuring and photocurrent performance, the oxygen reduction on P3HT always proceeds to produce H₂O₂ with 90%+ faradaic efficiency. The results of our efforts are demonstrations of how to tune and to increase both electrochemical capacitive and faradaic behavior of P3HT layers. Our findings indicate some limitations imposed by the P3HT itself, including low photovoltages and photochemical bleaching. Overall, these findings answer several open questions in the field of P3HT photoelectrochemical interfaces, and provide some general guidelines that can be applied to other organic semiconducting materials.