An Organic Semiconductor PEC Tandem Cell for Solar Water Splitting

The global-scale production of solar-fuels is urgently needed to progress towards a low-carbon energy economy. Solar-driven green hydrogen (H₂) production via water splitting stands out as a promising approach, and using photoelectrochemical (PEC) systems can potentially realize green H₂ in an economically competitive and scalable manner. PEC cells employing organic semiconductors (OS) are promising considering their compostion from widely availible carbon-based components, but despite encouraging advances with the half reactions, complete overall water splitting has remained a challenge. In a new report from LIMNO published in Advanced Energy Materials, we describe two advances we made with the organic semiconductor photocathode (semiconductor tuning and employing a self-assembled monolayer modified substrate) to afford robust photocathode operation under alkaline pH. These advances allowed the first demonstration of unassisted solar water splitting with a photoelectrochemical tandem cell employing organic semiconductors. The large-area (2.4 cm²) tandem cell had a predicted solar-to-hydrogen (STH) conversion efficiency of 0.8 %, and under unassisted two-electrode operation (1 Sun illumination) a stabilized photocurrent of 0.6 mA and an STH of 0.3 % was observed together with near unity Faradaic efficiency of H₂ and O₂. Our demonstration is a first step to validate the OS-based PEC tandem cell and further research will advance this technology toward practical application.