Photocurrent mechanism and photovoltaic properties of photo-electrochemical device based on PPAT and PPAT:TY blend

The solid state photo-electrochemical cell (PEC) solar energy conversion devices based on pure PPAT and PPAT:TY blend has been fabricated having structure ITO/nc-ZnO/PPAT or PPAT:TY/electrolyte/PEDOT:PSS-ITO and characterized. The redox properties of PPAT and TY were characterized using cyclic voltammetery (CV). The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have been estimated from their CV and UV–vis absorption spectra. The PPAT and PPAT:TY were used as sensitizer for ZnO nano-particle (nc-ZnO) in the film of PEC devices. Device that consist of PPAT:TY/nc-ZnO photoactive electrode showed improved photovoltaic performance over that consist of PPAT/nc-ZnO. This improvement attributed to the formation bulk heterojunction between PPAT and TY resulting efficient exciton dissociation into free charge carrier and photoinduced charge transfer. The photovoltaic performance of the device is further enhanced when the annealed PPAT:TY blend is used as sensitizer, which attributed to the increase in absorption and red shift in the absorption peak upon thermal annealing. This effect is due to the increased crystallinity of PPAT in the blend. PEC assembling with nc-ZnO adsorbed PPAT:TY blend using polar solvent treated PEDOT:PSS coating on ITO as a counter electrode, was studied. It was observed that when DMSO treated PEDOT:PSS counter electrode is used, the photovoltaic performance of the device is highest, which is attributed to enhanced conductivity of PEDOT:PSS and increased surface roughness. The PEC using carbon black (0.2 wt.%) modified DMSO treated PEDOT:PSS counter electrode reached a device efficiency of 5.54% under illumination 10 mW/cm2. This efficiency is higher than a PEC using untreated PEDOT:PSS as counter electrode. The thermal annealing of nc-ZnO photoelectrode improves the power conversion efficiency of the device, attributed to the increase crystallinity of the ZnO.