The effect of graphene quantum dots/ ZnS co‐passivation on enhancing the photovoltaic performance of CdS quantum dot sensitized solar cells

Abstract

The effect of graphene quantum dots (GQDs) as a passivating layer for cadmium sulfide (CdS) quantum dot-sensitized solar cell (QDSSC) has been investigated. GQDs were prepared by the liquid exfoliation method. The optical properties of GQDs were studied by UV-Vis and photoluminescence spectroscopies. The morphology of GQDs was studied by transmission emission morphology (TEM) analysis. Further, the photoexcitation behavior of GQDs has been studied in detail using emission spectroscopy and its effect on the photovoltaic performance of CdS QDSSC has been explored using J-V analysis. The efficacy of GQDs as passivation layer over the CdS loaded titanium dioxide (TiO2) photoanode in QDSSC is high and thereby improved the open-circuit voltage (Voc) (555 mV) compared to zinc sulfide (ZnS) passivated QDSSC (509 mV). As a result, the photoconversion efficiency (PCE) of GQD-passivated QDSSC is relatively enhanced up to 25% higher than that of ZnS-passivated QDSSC under similar conditions. A high PCE of 4.26% has been achieved for GQD/ZnS co-passivated QDSSC, which is 31% higher than ZnS-passivated QDSSC. Besides, the impedance analysis revealed low internal resistance and high charge recombination resistance in the GQD-passivated QDSSC when compared to other cells. The presence of GQD layer suppressed the recombination with high electron transport and thereby improved the PCE of QDSSC. The present study shows the possibility of using GQDs as an interfacial passivation layer between the sensitizer and electrolytes for enhancing the photovoltaic performance of CdS-based QDSSCs.