Enhancing the Performances of P3HT:PCBM-MoS3-Based H2-Evolving Photocathodes with Interfacial Layers

Organic semiconductors have great potential for producing hydrogen in a durable and economically viable manner because they rely on readily available materials and can be solution-processed over large areas. With the objective of building efficient hybrid organic-inorganic photoelectrochemical cells, we combined a noble-metal-free and solution-processable catalyst for proton reduction, MoS3, and a poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction (BHJ). Different interfacial layers were investigated to improve the charge transfer between P3HT:PCBM and MoS3. Metallic Al/Ti interfacial layers led to an increase of the photocurrent by up to 8 mA cm(-2) at reversible hydrogen electrode (RHE) potential with a 0.6 V anodic shift of the H2 evolution reaction onset potential, a value close to the open-circuit potential of the P3HT:PCBM solar cell. A 50-nm-thick C60 layer also works as an interfacial layer, with a current density reaching 1 mA cm(-2) at the RHE potential. Moreover, two recently highlighted1 figures-of-merit, measuring the ratio of power saved, Φsaved,ideal and Φsaved,NPAC, were evaluated and discussed to compare the performances of various photocathodes assessed in a three-electrode configuration. Φsaved,ideal and Φsaved,NPAC use the RHE and a nonphotoactive electrode with an identical catalyst as the dark electrode, respectively. They provide different information especially for differentiation of the roles of the photogenerating layer and catalyst. The best results were obtained with the Al/Ti metallic interlayer, with Φsaved,ideal and Φsaved,NPAC reaching 0.64% and 2.05%, respectively.