Solar Energy Materials & Solar Cells 90 (2006) 2413–2420 Electrical properties of porous silicon/polypyrrole heterojunctions M. Concepcio´n Arenas a,Ã , Hailin Hu a , J. Antonio del Rı´o a , Aaro´n Sa´nchez a , M.E. Nicho b a Centro de Investigacio´n en Energı´a, UNAM, Av. Xochicalco S/N, Temixco, Morelos, 62580, Me´xico b CIICAp-Universidad Auto´noma del Estado de Morelos, Cuernavaca, Morelos, Mexico Available online 18 April 2006 Abstract 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 V oc ¼ 135 mV, a fill factor of FF ¼ 0.25, a short circuit current density of J sc ¼ 8.58 mA/cm 2 and an energy conversion efficiency of n c ¼ 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 V oc ¼ 255 mV, J sc ¼ 54.4 mA/cm 2 , FF ¼ 0.26 and n c ¼ 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 KO and of 1 KO for n-Si/ PS(powder)/PPy junction. r 2006 Elsevier B.V. All rights reserved. Keywords: Porous silicon; Polypyrrole; Electrical properties; Photovoltaic effect 1. Introduction Since the discovery of visible photoluminescence on porous silicon (PS) at room temperature [1], a broad range of experimental and theoretical investigations have been ARTICLE IN PRESS www.elsevier.com/locate/solmat 0927-0248/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2006.03.014 Ã Corresponding author. Tel.: +52 55 56229747; fax: +52 55 56229742. E-mail addresses: mcaa@cie.unam.mx (M. Concepcio´n Arenas), hzh@cie.unam.mx (H. Hu).