Hydroxylated Organic Semiconductors for Efficient Photovoltaics and Photocatalytic Hydrogen Evolution

Organic semiconductors (OSCs)-based bulk heterojunctions (BHJ) have been widely applied for efficient organic photovoltaics (OPV) and recently also utilized as photocatalysts for hydrogen evolution reaction (HER). It is desirable for the BHJ to simultaneously harvest long-wavelength light and possess a high LUMO level which can maximize theoretical open-circuit voltage (Voc) for OPV and provide sufficient overpotential for HER. However, it remains challenging to obtain OSCs with a narrow bandgap and a shallow LUMO. To overcome this compromise, we design two hydroxyl-functionalized OSCs (BTP-FOH and BTP-2OH) as acceptors in the BHJ. Compared to hydroxyl-free BTP-4F, LUMO levels of BTP-FOH and BTP-2OH are gradually lifted with increased hydroxyl groups. Meanwhile, hydroxyl-induced intermolecular H-bonds augment the molecular alignment leading to red-shifted film absorptions in long-wavelength region. Moreover, hydroxyl groups result in variable aggregation behavior and hydrophilicity of the molecules, causing their different performances in OPV and in HER. While BTP-FOH-based BHJ delivers a higher efficiency of 16.71% in solar cells, BTP-2OH-based one acquires higher hydrogen evolution rate (102.1 mmol h-1 g-1) and EQE (9.17% at 800 nm, the highest value for OSC BHJ-based photocatalysts) in HER. Our work demonstrates that the hydroxylation is effective for designing acceptor materials with long-wavelength light utilization and high LUMO level for both light-driven applications.