Quasi solid-state quantum dot-sensitized solar cells with polysulfide gel polymer electrolyte for superior stability

In the case of sensitized solar cells, liquid electrolyte materials are the fundamental components due to its advantage of superior conductivity. However, in the typical day time, the temperature of the solar cell may rise due to the internal heating, which affects the liquid electrolyte and ultimately affects the solar cell performance and stability. Herein, we report the synthesis of polysulfide gel polymer electrolyte (GPE) for quasi solid-state quantum dot-sensitized solar cells (QS-QDSSCs) using easily available low-cost materials. Furthermore, the GPE is sandwiched between CdS quantum dot-based photoanode and CZTS/Pt-FTO counter electrode (CE). In the present study, initially, 50 wt% polyethylene glycol (PEG) as gelator and 50 wt% glycerol as plasticizer containing GPE is synthesized. In order to have the advantage of high phase transfer temperature (T-P), different molecular weight-based PEGs (PEG500, PEG1000, PEG2000, and PEG4000) are used. PEG4000-based GPE could achieve high T-P (> 60 degrees C). Moreover, in order to optimize the conductivity and activation energy of GPE, PEG4000 wt% is varied from 50 to 10 wt%. Additionally, electrochemical properties and photovoltaic performance of QS-QDSSCs prepared with different wt% of gelator in GPE are also studied. Superior power conversion efficiency (PCE) of 4.09% is achieved by QS-QDSSC prepared with 30 wt% PEG4000-based GPE. Furthermore, to enhance the conductivity of GPE, few drops of Li-TFSI are added, which ultimately leads to PCE enhancement (4.19%). Also, the stability of GPE-based QS-QDSSCs is studied. GPE-based QS-QDSSCs demonstrated more than 3.5 times stability (50 days) than liquid electrolyte-based QDSSCs (14 days).