Highly efficient indoor light quasi-solid-state dye sensitized solar cells using cobalt polyethylene oxide-based printable electrolytes

High-performance printable electrolytes (PEs) containing Co⁺²/Co⁺³ or I⁻/I₃⁻ redox-couple are prepared to fabricate quasi-solid-state (QS) dye-sensitized solar cells (QS-DSSCs) for room light environment applications. Polyethylene oxide (PEO) and poly(methyl methacrylate) (PMMA) are utilized to prepare PEs. Various parameters are regulated to obtain the optimal power conversion efficiencies (PCEs). For the I⁻/I₃⁻ system, the QS-DSSCs using PEO and PEO/PMMA PEs achieve nearly identical PCEs (16.32% and 16.40%, respectively) under the optimal conditions. However, the PCEs obtained for the Co⁺²/Co⁺³ system are markedly higher and the cell using PEO PE has a higher PCE (21.06%) than that using PEO/PMMA (18.14%). This difference is ascribed to the different composition of Li⁺ and Co⁺³ around the photoelectrode. The presence of Li⁺ around the interface will repel Co⁺³ away from the interface, decreasing the recombination of excited electrons to Co⁺³. According to the molecular structure, PMMA has more lone pair electrons to coordinate with Li⁺ ions, which will decrease the concentration of free Li⁺ more significantly than does by PEO. Therefore, the presence of PMMA will decrease and increase, respectively, the Li⁺ and Co⁺³ concentrations at the photoelectrode/electrolyte interface, resulting in more significant recombination of electrons to the Co⁺³. Consequently, the PCE of the PEO/PMMA cell is lower than that of the PEO cell. This effect doesn't occur in I⁻/I₃⁻ system because the concentration variation of negatively charged ions did not affect significantly the electrons recombination at the interfacial. By using this cobalt PE, a bifacial QS-DSSC can achieve PCEs of 17.22% and 14.25%, respectively, under front-side and back-side illumination by 200 lx T5 light. A sub-module QS-DSSC using the cobalt PE can attain a PCE of 12.56%.