EFFECT OF SIDE-CHAIN LENGTH ON RECTIFICATION AND PHOTOVOLTAIC CHARACTERISTICS OF POLY(3-ALKYLTHIOPHENE) SCHOTTKY BARRIERS

Schottky diodes of aluminium/poly(3-alkylthiophene) (P3AT)/indium-tin oxide (ITO) with large area (0.15-0.5 cm2) are prepared using the proposed new casting technique. The P3ATs investigated involve poly(3-butylthiophene) (P3BT), poly(3-octylthiophene) (P3OT) and poly(3-dodecylthiophene) (P3DDT), which are prepared using the chemical method. The diodes, in which P3AT behaves as a p-type semiconductor, exhibit a moderate rectifying behaviour and low leakage current. Photovoltaic measurements show a power conversion efficiency of about 10(-2)-10(-3)% at a light intensity of 0.5-5 mW/cm2, which decreases with increasing light intensity. The longer alkyl side-chain length of P3ATs can cause a lower rectifying effect, barrier height, depletion region width and photovoltaic conversion efficiency.