Investigation of counter electrode materials for gel polymer electrolyte based quantum dot sensitized solar cells

In this article, we report CdS based quantum dot sensitized solar cells (QDSSCs) with methylcellulose-polysulfide gel polymer electrolytes (GPEs) and platinum (Pt), gold (Au) or lead sulphide (PbS) counter electrodes. The optimized GPE has the composition of 30.7 wt.% methylcellulose, 67.4 wt.% Na2S, and 1.9 wt.% sulfur with an ionic conductivity of 0.18 S cm−1 at room temperature. The QDSSC fabricated with Pt counter electrode exhibits a power conversion efficiency (PCE) of 1.42% with a short-circuit current density (Jsc) of 7.30 mA cm−2, open circuit voltage (Voc) of 0.56 V and fill factor (FF) of 0.34. When Au is used as the counter electrode, the performance of the cell declined slightly with a PCE of 1.30%, Jsc of 10.59 mA cm−2, Voc of 0.47 V and FF of 0.26. With PbS as counter electrode, the PCE of the QDSSC enhanced to 2.90% with Jsc of 9.61 mA cm−2, Voc of 0.60 V and FF of 0.50. This corresponds to an efficiency enhancement of 104%. The good performance of PbS is attributed to the better catalytic activity of PbS for the electron transfer at the counter electrode/electrolyte interface.