Electrical properties of porous silicon/polypyrrole heterojunctions

Heterojunctions of porous silicon (PS) with polypyrrole (PPy) have been prepared and characterized. PS was formed by electrochemical anodization of p-type and n-type crystalline silicon (c-Si) wafers and PPy by electropolymerization of pyrrole. Current–voltage (I–V  ) characterizations of different PS/PPy structures were obtained in dark and under illumination. PPy forms a rectifying contact with PS layer on p-type c-Si substrate, but photovoltage was found in the heterojunctions of PPy on n-type c-Si with an open circuit of Voc=135mV, a fill factor of FF=0.25, a short circuit current density of Jsc=8.58 mA/cm2 and an energy conversion efficiency of nc=0.078%. However, when porous silicon powder is added between n-Si and PPy, the photovoltaic performance of this novel junction was significantly improved, giving Voc=255mV, Jsc=54.4 mA/cm2, FF=0.26 and nc=1.8%. By fitting the I–V curves with the modified diode standard equation, the serial resistance of n-Si/PPy junction was about 10 KΩ and of 1 KΩ for n-Si/PS(powder)/PPy junction.