Objective: Dye-sensitized solar cells (DSSC) have attracted much attention due to their low cost, easy fabrication and high energy conversion efficiency. However, the traditionally used liquid electrolytes make the sealing and long-term stability of DSSC problematic. Poly-3-hexyl-thiophene (P3HT), a hole conductor, was used in this study to substitute liquid electrolytes. The effect of self-organization of P3HT was studied by varying the experimental conditions.

Methods: Porous TiO₂ films were deposited on FTO glass and sintered. N3 dye was adsorbed onto TiO₂ films from ethanol solution. P3HT was dissolved in different solvents and deposited onto TiO₂/dye anodes by spin-coating. The drying process of P3HT layers was varied by controlling temperature, time, atmosphere, etc. Al counter-electrodes were deposited by evaporation. All cells were tested by a solar simulator with AM 1.5G illumination.

Results: It is found that different drying processes have dramatic influence on the performance of DSSC. The reason for the performance variations are related to the self-organization of P3HT film, which can be demonstrated by UV-vis spectra. The optimized drying process renders highest efficiency in DSSC.

Conclusions: The relationship between DSSC performance and self-organization of P3HT films can be explained by hole transport effectiveness. P3HT is a polymer with long chains. For the randomly arranged P3HT chains, holes can easily be recombined before reaching the counter-electrode, while they are more likely to transport freely and contribute to external current in an ordered P3HT film. High performance DSSC can be achieved by the effective hole transport.