Internal quantum efficiency higher than 100% achieved by combining doping and quantum effects for photocatalytic overall water splitting

Multiple exciton generation (MEG), where two or more electron–hole pairs are produced from the absorption of one high-energy photon, could increase the efficiency of light absorbing devices. However, demonstrations of the effect are still scarce in photocatalytic hydrogen production. Moreover, many photocatalytic systems for overall water splitting suffer from poor charge carrier separation. Here we show that a CdTe quantum dot/vanadium-doped indium sulphide (CdTe/V-In₂S₃) photocatalyst has a built-in electric field and cascade energy band structure sufficient to effectively extract excitons and separate carriers, allowing MEG to be exploited for hydrogen production. We achieve a tunable energy band structure through quantum effects in CdTe and doping engineering of V-In₂S₃, which induces a 14-fold enhancement in the CdTe/V-In₂S₃ interfacial built-in electric field intensity relative to pristine CdTe/V-In₂S₃. We report an internal quantum efficiency of 114% at 350 nm for photocatalytic hydrogen production, demonstrating the utilization of MEG effects. The solar-to-hydrogen efficiency is 1.31%.