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.