Ambient light harvesting with high-performance printable electrolyte in direct contact structured dye-sensitized solar cells

For the first time, printable polymer gel electrolytes (PGEs) of the copper-redox system were developed for fabricating quasi-solid-state dye-sensitized solar cells (QS-DSSCs) using a printing process. Furthermore, these PGEs were employed to prepare QS-DSSCs with a direct-contact structure. Poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) were chosen as gelators for the PGEs. For sandwich-structured DSSCs, the optimal composition of the PGE contains 7 wt% gelators, with a PEO to PMMA weight ratio of 8:2. The electrochemical impedance spectroscopy (EIS) analysis demonstrated that the presence of PMMA in the PGE can improve the charge transfer at the counter electrode/PGEs interface. This PGE was then employed to fabricate QS-DSSCs with a direct contact structure. The results demonstrated that QS-DSSCs with a direct-contact structure achieved a notably higher PCE of 35.42% under room light illumination, which is significantly higher than that obtained by a sandwich-structured cell (29.86 %). The EIS analysis of the DSSCs indicated that the smaller charge transfer distance of the direct-contact cell led to a downward shift of the Fermi level, higher charge recombination resistance and longer electron lifetime. Among these, charge recombination inhibition was the main factor contributing to the higher PCEs of the direct-contact cell.