Poly(3,4-ethylenedioxypyrrole) coating and poly(4-styrenesulfonate) polyanions enhance solar cell performance

摘要

Co-sensitized photoanode with nitrogen doped graphene particles (NGPs) and CdS capable of harvesting light efficiently in the visible region is combined with a poly(3,4-ethylenedioxypyrrole) (PEDOP)@carbon(C)-cloth based counter electrode (CE) for the first time. The conduction band of NGPs is wedged between that of CdS and TiO2, and charge separation is improved in TiO2/NGPs/CdS compared to TiO2/CdS, thus resulting in a power conversion efficiency (PCE), greater by 37% and 305% in comparison to TiO2/CdS and TiO2/NGPs cells. The electrolyte is a polysulfide/silica gel modified with a polyanionic additive of sodium poly(4-styrenesulfonate) (NaPSS). NaPSS polymer chains serve as a passivating layer at the photoanode/electrolyte interface and reduce back electron transfer, while simultaneously allowing efficient hole transfer to the electrolyte. An optimal NaPSS content is ascertained from the highest PCE, conductivity and longest photovoltage decay time achieved for the electrolyte with 5 wt% NaPSS, compared to electrolytes with lower and higher NaPSS contents. The efficacy of PEDOP@C-cloth as a CE for the solar cell is confirmed from a lower charge transfer resistance and a higher diffusion current density for polysulfide reduction at the CE/electrolyte interface compared to sole C-cloth. This amplified solar cell performance is attained owing to the synergy of all the three components: NGPs at the photoanode, NaPSS in the electrolyte and PEDOP at the CE thus manifesting in a PCE of 7.7% for the TiO2/NGPs/CdS/polysulfide/silica/NaPSS gel/PEDOP@C-cloth cell relative to 3.5% attained for the TiO2/CdS/polysulfide/silica gel/C-cloth cell.