Transparent bifacial dye-sensitized solar cells based on an electrochemically polymerized organic counter electrode and an iodine-free polymer gel electrolyte

Bifacial transparent dye-sensitized solar cells (DSSCs) assembled with a highly transparent poly(3,4-ethylenedioxythiophene) (PEDOT) counter electrode (CE) and a non-absorptive iodine-free polymer gel electrolyte were developed. The PEDOT CEs were obtained via a facile in situ electrochemical polymerization method. Different charge capacities were applied in the polymerization process, and the PEDOT CEs were optimized with high transparency (>90 %) and favorable activity for catalyzing the reaction between the redox couples in the electrolyte. The gel electrolyte was prepared using an ionic liquid (1,2-dimethyl-3-propylinmidazolium iodide, DMPII) as the charge transfer intermediate and a polymer composite (PEO/PVDF-HFP) as the gelator without the addition of iodine. Besides high conductivity, the iodine-free electrolyte presented non-absorption in visible light region. The assembled bifacial DSSC device showed a power conversion efficiency (PCE) of 6.35 % under front-side irradiation, and 4.98 % under rear-side irradiation with intensity of 100 mW cm⁻², which approached almost 80 % of that of the front-side irradiation. These promising results demonstrated the potential of these transparent organic CE and non-absorptive polymer gel electrolyte for further applications such as developing transparent bifacial photovoltaics.