ZnS-Passivated CdSe/CdS Co-sensitized Mesoporous Zn2SnO4 Based Solar Cells

• Mesoporous Zn2SnO4 sensitized by CdSe/CdS QDs were synthesized via a two-step sequential process.
• Assembled QDs were characterized by HRTEM and STEM mapping.
• Efficiency increase in CdSe/CdS co-sensitized Zn2SnO4 DSSCs is discussed.
• The role of ZnS passivation layer is discussed by impedance spectroscopy.

CdS and CdSe/CdS quantum dot (QD) sensitizers were assembled onto mesoporous ternary Zn2SnO4 photoanodes using a two-step sequential process of successive ionic layer absorption and reaction (SILAR) and chemical bath deposition (CBD) for QD-cosensitized solar cell applications. The assembled CdS and CdSe QDs were observed using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), high-resolution TEM (HRTEM), and STEM/energy-dispersive X-ray spectroscopy (EDS) elemental mapping. CdSe/CdS cosensitized Zn2SnO4-based cells showed a higher absorption onset position, a stepwise band-edge level alignment, and, thereby, an improved power conversion efficiency (PCE) of 1.628% under one-sun conditions, which is the best result obtained using mesoporous Zn2SnO4 reported to date. In addition, the effect of a ZnS passivation layer on the photovoltaic performance and aging behavior has been investigated. Electrochemical impedance spectroscopy (EIS) showed that the main role of the ZnS layer is to enhance the aging behavior of the CdSe/CdS/Zn2SnO4 cells by improving the electron lifetime and charge recombination.

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