Photocarrier generation and photovoltaic effect have been systematically studied in single layer ITO/poly(3-alkylthiophene)(MAT)/Al Schottky and double layer ITO/P3AT/perylene/metal heterojunction cells. It has been found that Ohmic contact formation takes place between ITO (Au) with MAT and Au (Ag, Al) with perylene derivatives. The double layer organic heterojunction device shows strong rectifying behavior with the rectification ratio of 1000 (at +/-2 V) and the ideality factor of 2.15. The maximum incident photon to electron conversion efficiency (IPCE) of 0.08% was found for the devices fabricated using regioregular poly(3-butylthiophene) (P3BT), which was 20 times higher than its regiorandom counterpart. In the case of double layer P-n junction cell IPCE was more than an order of magnitude higher than that of the single layer junction of regioregular P3BT/Al. (C) 2002 Elsevier Science B.V. All rights reserved.