Fabrication and characterization of plastic-based flexible dye-sensitized solar cells consisting of crystalline mesoporous titania nanoparticles as photoanodes

Abstract

We fabricated a highly efficient (with a solar-to-electricity conversion efficiency (η) of 5.51%), plastic-based, flexible dye-sensitized solar cell (DSSC). The photoanode was made of a crystalline mesoporous TiO₂ film using a low-temperature electrophoretic deposition (EPD) process and compression treatment. The crystalline mesoporous TiO₂ film was composed of secondary mesoporous TiO₂ nanoparticles (MTNs, ca. 260 nm in size), synthesized by an aggregation of primary TiO₂ nanocrystallites. In contrast to commercial TiO₂ nanoparticles (i.e., P90, ca. 15.9 nm in size) that are widely used in DSSCs, the synthesized MTN-based film exhibited a higher surface area and porosity that increased dye adsorption, promoted effective electron transport, and enhanced light scattering, as evidenced by analysis of reflectance and absorbance spectra, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). We also optimized the compression pressure for MTN- and P90-based DSSCs in order to achieve maximum efficiency. We further systematically investigated the cause for the enhanced conversion efficiency of MTN-based DSSCs by measuring incident photon-to-electron conversion efficiency (IPCE) curves and electrochemical impedance spectra (EIS). IPCE results explained the increase in the short-circuit photocurrent density (J_SC) for MTN-based DSSCs, and EIS results indicated that MTN-based DSSCs exhibited a larger diffusion coefficient (D_eff), longer effective diffusion length (L_n), longer electron lifetime (τ_e), and lower charge transfer resistance (R_k), resulting in a higher power conversion efficiency. The MTN-based DSSC fabricated in the study showed great potential for application in plastic-based DSSCs using room temperature procedures.