Photovoltaic properties of liquid-state photoelectrochemical cells based on PPAT and a composite film of PPAT and nanocrystalline titanium dioxide

We have studied the optical and photoelectrical properties of liquid state photoelectrochemical cells (PECs) based on photoactive electrodes based on poly (phenyl azo methane thiophene) (PPAT) and a composite film of nano-crystalline titanium dioxide (nc-TiO2) and PPAT. The device fabricated with nc-TiO2/PPAT photoactive electrode shows better performance with an open circuit voltage (Voc) 0.56 V, short circuit photocurrent (Jsc) = 0.87 mA/cm2 and fill factor (FF) = 0.58 under illumination with white light intensity of 10 mW/cm2. We have analyzed the experimental results by comparing the IPCE spectra of both devices. It is observed that the device with nc-TiO2/PPAT photoactive electrode shows better photovoltaic response as compared to the device based on PPAT photoactive electrode. This indicates that PPAT shows its p-type semiconducting behavior in the device based on PPAT, while in the device based on nc-TiO2/PPAT photoactive electrode, the PPAT acts as a sensitizer to nano-crystalline TiO2. The PEC based on TiO2/PPAT photoelectrode exhibit an exponential increase of low frequency device capacitance due to the diffusion of electrons along TiO2 network. Effect of iodine doping in PPAT on the photovoltaic performance of PEC have been also studied.