Advancing artificial photosynthesis with organic semiconductors

Solution processable pi-conjugated carbon-based (organic) materials are well-recognized as exceptional semiconductors in flexible (plastic) organic solar cells and light emitting diodes. Indeed, their unique ability to be engineered at the molecular level and inexpensively processed by solution-based roll-to-roll techniques, gives them great promise for economical and high-performance use at global scale. However, their application to the direct conversion of solar energy into chemical fuels (artificial photosynthesis) has been limited by their poor stability under photoelectrochemical operation conditions.

In a new paper recently published in JACS, the LIMNO lab at EPFL reports a breakthrough in the use of organic semiconductors in the conversion of sunlight into hydrogen via water splitting. Through a careful study of the material stability, it was discovered that replacing the commonly-used fullerene-based electron acceptor with a perylene diimide-based polymer drastically increases operational stability. Moreover, it was identified that limiting the photogenerated electron accumulation at the organic/water interface is a requirement for stable operation. These insights were leveraged to extend the stability of solar-driven hydrogen production using MoS₃, MoP or RuO₂ water reduction catalyst overlayers demonstrating unprecedented robustness without a protection layer. The reported performance represents a new benchmark for organic semiconductor photocathodes for solar fuel production and also advances the understanding of stability criteria for organic semiconductor/water junction-based devices.