Enhancing quasi solid-state dye-sensitized solar cell performance using mixed-polymer gel electrolytes: the influence of low and high molar weight polymers

Gel polymer electrolytes (GPEs) are crucial in quasi-solid-state dye-sensitized solar cells (DSSCs) due to their chemical and physical stability, enhanced safety, and improved performance, which boosts ionic conductivity. This study presents the enhancing gel polymer electrolyte properties intended for DSSCs by blending low and high molar weight variants of the same polymer. The hot press method was used to synthesize the polymer blend electrolyte, the resulting in electrolyte gave a notable improvement in DSSC performance. The blend incorporates polyethylene oxide (PEO, MW 4,000,000) and its lower molar weight counterpart, polyethylene glycol (PEG, MW 4000). The ionic conductivities of the GPEs were assessed via impedance analysis. The GPE with 100% PEG achieved the highest ionic conductivity (10.30 mS cm⁻¹) but was liquid-like, while 100% PEO showed the lowest conductivity (5.23 mS cm⁻¹) with a solid-state nature. A blend with a 3:1 PEO-to-PEG ratio exhibited intermediate conductivity and a gel-like consistency. The electrolyte having molar composition PEO_(7.5)PEG_(2.5)EC₍₄₀₎PC₍₄₀₎Hex₄NI_(0.8)LiI_(1.2)I_2(0.2) in DSSC yielded an extremely high 8.76% power conversion efficiency and a short-circuit current density of 13.80 mA cm⁻². This electrolyte exhibited ionic conductivity of 6.86 mS cm⁻¹ 30 °C. The lowest efficiency was observed for the 100% PEO content. The study demonstrated a significant efficiency improvement of 38.17% and 36.45% in blend polymer electrolyte-based DSSCs compared to single polymer electrolytes with PEO and PEG, respectively. Conductivity in the GPEs followed Vogel–Tamman–Fulcher behavior. The DSSCs utilized N719 dye-sensitized TiO₂ nanoparticle multilayer photoanodes and Pt counter electrodes. The results indicate that combining low and high molar weight polymers in the electrolyte significantly boosts DSSC efficiency. Current efforts aim to refine polymer composition and understand the mechanisms behind the efficiency enhancement in mixed-phase gel polymer electrolytes.