The constructive role of ZnSe passivating layer on the photovoltaic performance of the fast-fabricated CdS/CdSe quantum dot sensitized solar cells

Abstract

In this research CdS and CdSe co-sensitized quantum dot sensitized solar cells were fabricated and the photovoltaic (PV) performance was improved. CdS quantum dots (QDs) layer was deposited on nanocrystalline TiO2 scaffold through the conventional successive ionic layer adsorption and reaction (SILAR) method. The CdSe nanocrystals film was also over-coated by an improved, fast and effective chemical bath deposition (CBD) approach. The power conversion efficiency was quite increased by application of a ZnSe passivating layer. This electron blocking layer could reduce the back-recombination rate of electrons with the electrolyte. That is while the photo-created holes are not blocked and could be well-transported based on the corresponding flat-band energy diagram of the fabricated device. The ZnSe over-layer was formed through a controlled SILAR process while the Se source was quite protected under the Ar gas flow during the deposition. Different number of SILAR cycles was applied for the ZnSe film formation and photovoltaic characteristics were investigated. The results demonstrated that the optimized cell with a ZnSe passivation layer deposited in three specific SILAR cycles represented a Jsc of 17.7 mA/cm2, Voc of 594 mV, FF of 0.5 and maximum power conversion efficiency of 5.3%. This efficiency was enhanced about 70% compared to that of the reference cell which was not passivated with ZnSe QDs layer.