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–Fe 2 O 3 /Ge–Fe 2 O 3 ) 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 Fe 2 O 3 (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.