Fabrication of flexible and efficient dye sensitized solar cells using modified TiO₂ electrode at low-temperature annealing process

The development of low temperature film production method is necessary in order to develop flexible dye sensitized solar cells (DSSCs) on the plastic films. Herein, we have developed a novel low-temperature (50 °C) annealing process for the successful fabrication flexible DSSCs on ITO/PEN substrate. By performing DSSC studies (morphology, UV-absorption spectra, I-V curve, IPCE and impedance) on various combinations of different TiO₂, we aimed to find out the optimum conditions to achieve maximum performance. Remarkably, the photoelectric conversion efficiency of the cell with compression pressure of 150 kg/cm² is obtained to be 3.86% which is 2.95 fold higher than that obtained without pressure. The mixing ratio between nano-sized (anatase-TiO₂), middle sized (DP-25) and large sized (QF1125) TiO₂ particles is optimized. The optimum mixing ratio between DP-25 and anatase-TiO₂ is studied (LDP25 series). 8:2 ratio of DP25:a-TiO₂ (named as LDP25-2) has shown maximum DSSC characteristics. Subsequently, the LDP25-2 is mixed with various amounts of QF1125 TiO₂ particles. The mixture containing 1 wt.% of QF1125 and 99 wt.% of LDP25-2 (named as LDP25-2.1) has shown maximum efficiency of 4.62%. Overall, the photoelectric conversion efficiency increases from 1.3% (for only DP25 at 0 kg/cm² pressure) to 4.62% (optimum mixing of a-TiO₂, DP-25 and QF-1125).