Thermally-enhanced charge collection boosts photoelectrochemical performance of hematite

Abstract The application of transition metal oxides in optoelectronics holds significant promise. However, their performance is often limited by small polaron hopping, a charge transport mechanism that reduces carrier mobility and collection efficiency. Therefore, improving small polaron hopping is crucial for enhancing charge collection. In this work, we propose a direct approach to effectively enhance the photoelectrochemical (PEC) performance of hematite by leveraging the thermal nature of polaron hopping. As a result, a photocurrent density of 4.53 mA/cm 2 at 1.23 V vs. RHE was achieved by heating the photoanode to 70 °C. By combining carrier dynamics analysis with charge collection modeling, we demonstrate that heating facilitates small polaron hopping, thereby increasing carrier mobility and improving the collection efficiency of hematite photoanodes. Our work provides clear explanations of the thermal-activated small polaron hopping mechanism, offering a simple yet effective strategy for enhancing the PEC performance of transition metal oxides.