An organic solar cell based on a poly-3-hexylthiophene (P3HT): phenyl-C 61 -butyric acid (PCBM) bulk hetero-junction was directly coupled with molybdenum sulfide resulting in the design of a new type of photocathode for the production of hydrogen. Both the light-harvesting system and the catalyst were deposited by low-cost solution-processed methods, i.e. spin coating and spray coating respectively. Spray-coated MoS 3 films are catalytically active in strongly acidic aqueous solutions with the best efficiencies for thicknesses of 40 to 90 nm. The photocathodes display photocurrents higher than reference samples, without catalyst or without coupling with a solar cell. Analysis by gas chromatography confirms the light-induced hydrogen evolution. The addition of titanium dioxide in the MoS 3 film enhances electron transport and collection within thick films and therefore the performance of the photocathode.

Organic semiconductors have great potential for producing hydrogen in a durable and economically viable manner, as they rely on readily available materials and can be solutionprocessed 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, MoS 3 , and a poly-(3-hexylthiophene):phenyl-C 61 -butyric acid methyl ester (P3HT:PCBM) bulk heterojunction (BHJ). Different interfacial layers were investigated to improve the charge transfer between P3HT:PCBM and MoS 3 . Metallic Al\Ti interfacial layers led to an increase of the photocurrent up to 8 mA cm −2 at reversible hydrogen electrode (RHE) potential with a 0.6 V anodic shift of the HER onset potential, a value close to the open circuit potential of the P3HT:PCBM solar cell. A 50 nm thick C 60 layer also works as interfacial layer, with current density reaching 1 mA cm −2 at RHE potential. Moreover, two recently highlighted 1 figures-of-merit, measuring the ratio of power saved, Φ saved,ideal and Φ saved,NPAC , were evaluated and discussed to compare the performances of various photocathodes assessed in a three-electrode configuration. Φ saved,ideal and Φ saved,NPAC use the RHE and a non-photoactive electrode with identical catalyst as dark electrode, respectively. They provide different information especially for the differentiation of the role of the photogenerating layer and the role of the catalyst. Best results were obtained with the Al\Ti metallic interlayer, with Φ saved,ideal and Φ saved,NPAC reaching 0.64 % and 2.05 % respectively.