Influence of Polymer Gel Electrolyte on the Performance of Dye-Sensitized Solar Cells Analyzed by Electrochemical Impedance Spectroscopy

The effects of gel electrolyte polymer matrix structure and composition on the photovoltaic properties of quasi-solid state dye-sensitized solar cells (DSSCs) were investigated using two series of copolymers, poly(hydroxy ethyl methacrylate-N-vinyl) pyrrolidone P(HEMA-NVP) and poly(methyl methacrylate-N-vinyl pyrrolidone) P(MMA-NVP), by electrochemical impedance spectroscopy (EIS). P(HEMA-NVP) copolymers with various crosslinking agent and N-vinyl pyrrolidone (NVP) contents, as well as P(MMA-NVP) copolymers with various NVP content, absorbed liquid electrolyte to form gel electrolytes HGeII, HGeIII, and MGeI, respectively. It was found that with increasing copolymer P(HEMA-NVP) crosslinking agent content, from 0.1 to 0.6% (w), the power conversion efficiency (eta) of DSSCs based on HGell initially increased and then decreased. A maximum conversion efficiency of 5.54% at 100 mW.cm(-2) was observed when crosslinker content was 0.4% (w). Meanwhile, we compared the parameters of DSSCs based on HGeIII with those of DSSCs based on MGeI. The conversion efficiencies of the former, which contained hydroxy groups, were all higher than those of the latter, while the open circuit voltages (V-oc) of the latter were larger than those of the former. DSSCs assembled with HGeIII with a HEMA content of 60% exhibited the highest conversion efficiency, at 100 mW.cm(-2). Electrochemical impedance spectroscopy (EIS) investigations showed that copolymer crosslinking structure affected the internal resistance and ionic conductivity of the resulting DSSCs, while addition of hydroxy groups decreased the interfacial resistance. Thus, the photovoltaic performance of DSSCs can be improved by tuning the crosslinking structure and the hydroxy content of the copolymer.