Dextran based highly conductive hydrogel polysulfide electrolyte for efficient quasi-solid-state quantum dot-sensitized solar cells

Highly conductive hydrogel polysulfide electrolyte is first fabricated using dextran as gelator and used as quasi-solid-state electrolyte for quantum dot-sensitized solar cells (QDSSCs). The hydrogel electrolyte with gelator concentration of 15 wt% shows almost the same conductivity as the liquid one. Moreover, its liquid state at elevated temperature allow for the well penetration into the pores in electrodeposited CdS/CdSe co-sensitized TiO2 photoanode. This gel electrolyte based QDSSC exhibits power conversion efficiency (eta) of 3.23% under AG 1.5 G one sun (100 mW cm(-2)) illumination, slightly lower than that of liquid electrolyte based cell (3.69%). The dynamic electron transfer mechanism of the gel and liquid electrolyte based QDSSC are examined by electrochemical impedance spectroscopy (EIS) and controlled intensity modulated photocurrent/photovoltage spectroscopy (CIMPS/IMVS). It is found that the electron transport in gel electrolyte based cell is much faster than the liquid electrolyte based cell but it tends to recombine more easily than the latter. However, these differences fade away with increasing the light intensity, showing declining electron collection efficiency at higher light intensity illumination. As a result, a conversion efficiency of 4.58% is obtained for the gel electrolyte based quasi-solid-state QDSSC under 0.12 sun illumination. The high conductivity and the good permeation of gel electrolyte may contribute mainly to its excellent photovoltaic performance. (C) 2013 Elsevier Ltd. All rights reserved.