A novel multifunctional polymer ionic liquid as an additive in iodide electrolyte combined with silver mirror coating counter electrodes for quasi-solid-state dye-sensitized solar cells

Abstract

A novel multifunctional polymer ionic liquid poly(oxyethylene)-imide-2,2,6,6-tetramethyl-1-piperidinyloxy (POEI-TEMPO) was successfully prepared and used as an additive in iodide electrolyte in quasi-solid-state dye-sensitized solar cells (QSS-DSSCs). The POEI segment in the electrolyte has good mechanical strength; meanwhile, the TEMPO organic radical contains nitroxide as the redox couple (RN-O˙/RNO⁺) acting as a superior mediator in DSSCs. TEMPO has a number of favorable properties, such as fast and reversible redox kinetics, large apparent diffusion coefficient (D_app), positive redox potential, and facile electron self-exchange reaction. As a result, DSSCs were composed of a POEI-TEMPO/iodide electrolyte and a Pt-coated FTO layer on glass as a normal counter electrode (PtCE), whereas the other side of the glass was coated with silver mirror coating (SMC) as the bifacial PtCE/SMC cell. DSSC exhibited a maximum photoelectric conversion efficiency (η) of 9.83%, open-circuit voltage (V_OC) of 812.84 mV, and short-circuit current density (J_SC) of 16.60 mA cm⁻² under 1 sun (AM 1.5 G, 100 mW cm⁻²), whereas the value of η reached 25.99% under an indoor condition with 6000 lux (1.89 mW cm⁻²). Moreover, when POEI-TEMPO is used as an additive, the bifacial cell maintains its high performance with a reasonable long-term stability. The finding is expected to have a practical impact on harvesting the ambient light energy and extending the cell lifetime.