Study On Photoelectrochemical Performance Of Energy Band Controllable Quantum Dots Based On Core-shell Structure

The conversion of solar energy into clean fuels energy is of great significance to address the growing global energy demand.Photoelectrochemical?PEC?cell has demonstrated great potential for efficient conversion of solar energy into hydrogen fuel since the pioneer work of Fujishima et al.In this study,the wide band gap semiconductor?TiO₂?was used as the working electrode.Due to the limited light absorption in the ultraviolet?UV?region,the relative system conversion efficiency was lower.Colloidal quantum dots?CQD?have excellent optical properties and are used to prepare semiconductor photoelectrodes to effectively improve the efficiency of solar-powered PEC cells.Previous studies found that the core-shell heterostructure can effectively passivate the trap states on the surface of quantum dots?QD?,suppress non-radiative recombination,and enhance the photo-/chemical-stability of bare QDs.Core-shell quantum dots can achieve precise control of electrochemical performance by controlling the chemical composition and size of the core/shell materials.As an example,growing a CdS shell on CuInS₂?CIS?QDs can form a quasi-II type band arrangement,wherein the delocalized electrons in the shell and localized holes confined in the core can lead to efficient charge separation and enhancing the device performance in the corresponding QDs-based solar energy conversion applications,making CIS/CdS based PEC cells show great potential for solar harvesting.However,although the optical properties of CIS/CdS core/shell QDs with quasi-type II band structure were extensively studied and relevant QDs-sensitized solar cells?QDSCs?were reported,there is no comprehensive investigation of such core/shell QDs for solar-driven PEC cells applications,to the best of our knowledge.Particularly,the shell thickness engineering for optimized device performance is not explored yet.Here,we successfully synthesized the pyramid-shaped CIS QDs by chemical synthesis.And a series of quasi-type II CIS/CdS core/shell QDs with wurtzite?WZ?crystal structure of different sizes were successfully synthesized by thermal injection via controlling the injection of Cd and S precursor stock solution.Photofluorescence spectroscopy?PL?analysis showed that with the increase of CdS shell thickness,the PL peak showed obvious redshift?from⁷13 to 771 nm?and extended PL lifetime?up to⁵68ns?,which indicated that CIS/CdS core/shell QDs were quasi-type II band alignment.The carrier dynamics was studied by transient spectroscopy?TA?,and the reason of prolonging the PL lifetime was analyzed.It was proved that controlling the band alignment by controlling the size could improve the delocalization effect of electron in space.Theoretical simulation shows that the increase of the thickness of CdS shell can improve the delocalization effect of electrons in space,and it also proves the quasi-type II band alignment of CIS/CdS core/shell QDs.This theoretically supports optical analysis.Finally,these QDs are applied to QDs sensitized PEC cells.Under simulated 1 sun illumination,the saturation photocurrent density reached 6mA/cm² at the best,and the stability test showed that the performance reached 78.9%of the initial value after 2 hours.The experimental and theoretical hydrogen evolution of the CIS/CdS core/shell QDs-based device were further tested by a gas chromatograph?GC?system and calculated the Faraday efficiency was 58%.The effective and stable PEC performance shows that we have successfully applied CIS/CdS core/shell QDs to PEC devices,and tailored the band alignment to tailoring optical performance,so as to maximize the performance of core/shell QDs-based device.