Toward Stable Solar Hydrogen Generation Using Organic Photoelectrochemical Cells

Organic photoactive materials are promising candidates for the generation of solar fuels in terms of efficiency and cost. However, their low stability in aqueous media constitutes a serious problem for technological deployment. Here we present organic photocathodes for the generation of hydrogen in aqueous media with outstanding stability. The device design relies on the use of water-resistant selective contacts, which protect a P3HT:PCBM photoactive layer. An insoluble cross-linked PEDOT:PSS hole-selective layer avoids delamination of the film, and an electron-selective TiO_x layer in contact with the aqueous solution electrically communicates the organic layer with the hydrogen-evolving catalyst (Pt). We developed a novel method for the synthesis of the TiO_x layer compatible with low-temperature conditions. Tuning the thickness of the TiO_x/Pt layer leads to a trade-off between the achievable photocurrent (∼1 mAcm^–2) and the stability of the photocathode (stable hydrogen generation of 1.5 μmol h^–1 cm^–2 for >3 h).