Polyvinyl Acetal-based Quasi-Solid-Sate Electrolytes and Their Application in Dye-sensitized Solar Cells

Polyvinyl formal (PVF) and polyvinyl butyral (PVB) as polymer frameworks are used to prepare quasi. solid. state electrolytes loaded with I-2 and LiI, which are further applied in dye. sensitized solar cells (DSCs) to improve the stability of DSCs. FTIR spectra, thermodynamic and electrochemical methods are used to characterize the functional group of the polymers and the conductivity of the quasi. solid. state electrolytes. These results show that the oxygen atoms of C = O and O-C-O in the polymers (PVF and PVB) can interact with Li+ of LiI by coordination effect, promoting the ionization of LiI and facilitating the charge transport. Through the comparison between PVF and PVB, it can be also found that the propyl side chain of PVB has positive influence on the thermodynamic and electrochemical performance, where the DSCs with PVB exhibit better photovoltaic performance. By optimizing the composition of electrolytes, the ionic conductivity of PVF and PVB. based quasi. solid. state electrolytes can reach the maximum ionic conductivity of 2.5 mS . cm(-1) (PVF) and 4. 2 mS . cm(-1) (PVB), with the concentration of LiI at 0. 7 mol . L-1. Under this condition, the diffusion. limiting current density of PVF and PVB. based quasi. solid. state electrolytes can achieve 10. 05 mA . cm(-2)(triiodide ionic diffusion constant = 1. 84 x 10(-6) cm(2) . s(-1)) and 17. 89 mA . cm(-2) (triiodide ionic diffusion constant = 3. 23 x 10(-6) cm(2) . s(-1)), respectively. Impedance plots of the quasi. solid. state DSCs reflect that the PVB. based DSCs have a higher charge. transport resistance (R-ct = 118. 9 Omega) than that of PVF. based DSCs (R-ct = 49. 57 Omega) and effectively suppress the dark reaction due to the steric hindrance of the propyl side chain. Eventually, the dye. sensitized solar cells based on these two electrolytes attain satisfactory energy conversion efficiency of 4. 18% (PVF) and 6. 06% (PVB) and excellent long. term stability, which renders only a tiny decline of the efficiency of DSCs and maintain the efficiency of DSCs at above 90% of the origina