An alternative method to build organic photodiodes

We demonstrate a new method to build inverted organic photodiodes with highly conducting polymer anodes. In the inverted design the cathode is deposited first, followed by the deposition of the active material and finally the anode. A cathode of bismuth was vacuum evaporated followed by the evaporation of a capping layer of C-60. A semiconducting polymer, poly(3-(4'-(1,4,7-trioxaoctyl)phenyl)thiophene) (PEOPT) was then spin-coated on the cathode, followed by a surface energy modification step and a subsequent spin-coating of the anode, a solution of glycerol and the conducting polymer poly(3,4-ethylenedioxythiophene) with the polyelectrolyte poly(4-styrenesulfonate) (PEDOT-PSS). As the pristine PEOPT was too hydrophobic to spin-coat the aqueous based PEDOT-PSS, the semiconducting polymer was silanized with 3-glycidoxypropyltrimethoxysilane to increase its surface energy before spin-coating of the PEDOT-PSS solution. The device geometry was proven successful by current-voltage measurements of devices in dark and under illumination. (C) 2003 Elsevier B.V. All rights reserved.