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

Multiple exciton generation can potentially improve the efficiency of solar-driven devices, but its demonstration for solar fuel production is rare. Here the authors show that quantum efficiencies above 100% are achievable in a water splitting photocatalyst, implying the presence of multiple exciton generation effects. 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%.