An Organic Semiconductor Photoelectrochemical Tandem Cell for Solar Water Splitting

Abstract

Photoelectrochemical cells employing organic semiconductors (OS) are promising for solar-to-fuel conversion via water splitting. However, despite encouraging advances with the half reactions, complete overall water splitting remains a challenge. Herein, a robust organic photocathode operating in near-neutral pH electrolyte by careful selections of a semiconducting polymer bulk heterojunction (BHJ) blend and organic charge-selective layer is realized. The optimized photocathode produces a photocurrent density of >4 mA cm−2 at 0 V vs the reversible hydrogen electrode (VRHE) for solar water reduction with noticeable operational stability (retaining ≈90% of the initial performance over 6 h) at pH 9. Combining the optimized BHJ photocathode with a benchmark BHJ photoanode leads to the demonstration of a large-area (2.4 cm2) organic photoelectrochemical tandem cell for complete solar water splitting, with a predicted solar-to-hydrogen (STH) conversion efficiency of 0.8%. Under unassisted two-electrode operation (1 Sun illumination) a stabilized photocurrent of 0.6 mA and an STH of 0.3% are observed together with near unity Faradaic efficiency of H2 and O2 production.