Recombination control in high-performance quantum dot-sensitized solar cells with a novel TiO2/ZnS/CdS/ZnS heterostructure

Abstract

Charge recombination occurring at the TiO₂/QDs/electrolyte interface is a crucial factor that limits the power conversion efficiency (η) of quantum dot-sensitized solar cells (QDSSCs). This paper presents a new approach by inserting a ZnS layer between the TiO₂ and CdS/ZnS to prepare a TiO₂/ZnS/CdS/ZnS sensitized photoelectrode for QDSSC applications. The CdS QDs and ZnS passivation layers were deposited using a reproducible and controlled successive ionic layer adsorption and reaction method. The TiO₂/ZnS/CdS/ZnS based QDSSCs exhibited a power conversion efficiency (η) value of 3.69%, which is significantly higher than the 3.02% and 2.09% observed for solar cells with a TiO₂/CdS/ZnS device and without a passivation layer (TiO₂/CdS), respectively. The elevated performance of the TiO₂/ZnS/CdS/ZnS-based QDSSCs was attributed to the pre-assembled ZnS layer enhancing the light harvesting and acting as a blocking layer to shield the TiO₂ core from the outer QDs and the electrolyte, thereby retarding the interfacial recombination of electrons from the TiO₂ with the electrolyte or with the QDs. Electrochemical impedance spectroscopy and open circuit voltage decay measurements showed that the TiO₂/ZnS/CdS/ZnS-based QDSSCs inhibit charge recombination remarkably at the photoanode/electrolyte interface and prolong the electron lifetime.