Poly(1,4-Diethynylbenzene) Gradient Homojunction with Enhanced Charge Carrier Separation for Photoelectrochemical Water Reduction

As appealing photoelectrode materials for photoeletrochemical hydrogen evolution reaction (PEC HER), conjugated polymers still show poor PEC HER performance as a result of their serious recombination of photogenerated electrons and holes. Herein, a novel design of gradient homojunction is demonstrated by controlled copolymerization of 1,4-diethynylbenzene (DEB) and 1,3,5-triethynylbenzene (TEB). The as-built gradient distribution of TEB monomer in poly(1,4-diethynylbenzene) (pDEB) leads to continuous band bending engineering, which constitutes a gradient homojunction. Under AM 1.5G irradiation and in 0.1 m Na ₂ SO ₄ aqueous solution, the as-fabricated pDEB gradient homojunction exhibits a charge separation efficiency of 0.27% at 0.3 V versus reversible hydrogen electrode (RHE), which is 3.4 and 1.7 times higher than those for pure pDEB and the traditionally designed pDEB homojunction. As a result, the photocurrent of the pDEB gradient homojunction unprecedentedly reaches 55 µA cm ⁻² at 0.3 V versus RHE, which is much higher than 19 µA cm ⁻² for pure pDEB, 32 µA cm ⁻² for the pDEB homojunction, and state-of-the-art organic photocathodes, e.g., g-C ₃ N ₄ (≈1−32 µA cm ⁻² ). This work opens up a new window for the design of gradient homojunctions and will advance the exploration of high-performance organic photoelectrodes.