Effect of moisture (in solid polymer electrolyte) on the photosensitivity of conducting polypyrrole sensitized by prussian blue in solid-state photocells

The effect of small concentration of dispersed prussian blue (PB) [in solid polymer electrolyte viz polyvinyl alcohol (PVA) with phosphoric acid] on the photocurrents were studied (in wet state and in dry state of solid polymer electrolyte) in solid state photocells fabricated using conducting polypyrrole (PPy). These exhibit good photoresponse to visible light: photocurrents being 20 to 25 times greater than the dark currents depending upon the concentration of the sensitizer. The current–voltage (I–V) characteristics in such cells reveals that the charge transport is mainly governed by the space charge effects and the sensitization effects are due to the lowering of the potential barrier formed at the polypyrrole (PPy)/polyvinyl alcohol (PVA) interface under photoexcitation. Also, sensitization effects were studied in the wet state and in dry state of solid polymer electrolyte (PVA). It has been observed that the moisture content in the solid polymer electrolyte reduces the photosensitivity factor (S=Il/Id, where Il is the light current and Id is the dark current), since it increases the ionic conductivity in the solid polymer electrolyte thereby increasing the dark current values which results in overall decrease in the photosensitivity factor (S). The importance of the other factors such as dye concentration, dye aggregation etc. have been explained on the basis of the experimental observations. The sensitization effects are explained on the basis of the energy band diagram of the materials forming the photocells.