Utilizing a Siloxane-Modified Organic Semiconductor for Photoelectrochemical Water Splitting

We explore the potential of employing diketopyrrolopyrrole (DPP) based π-conjugated OSs as a hole transport layer material in heteroatom-doped hematite (Ti-Fe₂O₃/Ge-Fe₂O₃) photoanodes for efficient photoelectrochemical water splitting. The siloxane-modified π-conjugated polymer (P_Si) with a high carrier mobility and crystallinity revealed great potential to extract holes by forming a built-in potential with hematite photoanodes while showing high stability in an alkaline electrolyte for photoelectrochemical water oxidation. Because of the easy hole extraction and subsequent fast hole transport property of the P_Si interlayer between NiFe(OH)_x and Ge-doped porous Fe₂O₃(Ge-PH), NiFe(OH)_x/P_Si/Ge-PH showed a 1.8-fold increase in photocurrent density (4.57 mA cm^-2 at 1.23 V_RHE) with a cathodic shift of the onset potential (0.735 V_RHE) and good stability for 65 h compared to Ge-PH. This study demonstrates the successful use of inherently unstable π-conjugated OSs as a hole extracting/transport medium in a photoanode, addressing the intrinsic recombination issues of hematite for efficient and stable water splitting.