Hematite is one of the most promising photoanode materials for the study of photoelectrochemical (PEC) water splitting because of its ideal bandgap with sufficient visible light absorption and stability in alkaline electrolytes. However, owing to the intrinsically high electron-hole recombination, the PEC performance of hematite is still far below that expected. The efficient charge separation can be achieved via growth of FeOOH on hematite photoanode. In this study, hematite nanostructures were successfully grown on the surface of iron foil by the simple immersion deposition method and thermal oxidation treatment. Furthermore, cocatalyst FeOOH was successfully added to the hematite nanostructure surface to improve charge separation and charge transfer, and thus promote the photoelectrochemical water splitting. By utilizing the FeOOH overlayer as a cocatalyst, the photocurrent density of hematite exhibited a substantial 86% increase under 1.5 V_RHE, while the onset potential showed an apparent shift towards the cathodic direction. This can be ascribed to the high reaction area for the nanostructured morphology and high electrocatalytic activity of FeOOH that enhanced the amount of photogenerated holes and accelerated the kinetics of water splitting.

Exciton dissociation and charge transport are important processes in the photoelectric conversion of organic solar cells (OSCs), directly affecting the performance of OSCs. In order to facilitate exciton dissociation, phase separation size should be as small as possible. However, for the sake of continuous charge transport, a large phase separation size is also necessary. To balance these two conflicting needs, it is of utmost importance to regulate the phase separation of the active layer. This Review mainly elaborated the smart tactics commonly adopted to phase separation optimization, aiming to understand how these treatments affect both the active layer phase separation and the performance of OSCs. Furthermore, we present an outlook on the new opportunities of phase separation regulation of the active layer. Finally, this Review may provide some reference for the researchers engaged in the research of OSCs.

Considering the poor conductivity of Fe₂O₃ and the weak oxygen evolution reaction associated with it, surface hole accumulation leads to electron hole pair recombination, which inhibits the photoelectrochemical (PEC) performance of the Fe₂O₃ photoanode. Therefore, the key to improving the PEC water oxidation performance of the Fe₂O₃ photoanode is to take measures to improve the conductivity of Fe₂O₃ and accelerate the reaction kinetics of surface oxidation. In this work, the PEC performances of Fe₂O₃ photoanodes are synergistically improved by combining loaded an FeOOH cocatalyst and oxygen vacancy doping. Firstly, amorphous FeOOH layers are successfully prepared on Fe₂O₃ nanostructures through simple photoassisted electrodepositon. Then oxygen vacancies are introduced into FeOOH-Fe₂O₃ through plasma vacuum treatment, which reduces the content of Fe-O (O_L) and Fe-OH (-OH), jointly promoting the generation of oxygen vacancies. Oxygen vacancy can increase the concentration of most carriers in Fe₂O₃ and form photo-induced charge traps, promoting the separation of electron holes and enhancing the conductivity of Fe₂O₃. The other parts of -OH act as oxygen evolution catalysts to reduce the reaction obstacle of water oxidation and promote the transfer of holes to the electrode/electrolyte interface. The performance of FeOOH-Fe₂O₃ after plasma vacuum treatment has been greatly improved, and the photocurrent density is about 1.9 times higher than that of the Fe₂O₃ photoanode. The improvement in the water oxidation performance of PEC is considered to be the synergistic effect of the cocatalyst and oxygen vacancy. All outstanding PEC response characteristics show that the modification of the cocatalyst and oxygen vacancy doping represent a favorable strategy for synergistically improving Fe₂O₃ photoanode performance.