ELSEVIER Synthetic Metals 83 (1996) 239-243 Photoconduction and photovoltaic effects from a conjugated polymer poly-tert-butyl-isothionaphthalene S. Curran a,., S. Roth a, A.P. Davey b A. Drury b W. Blau b a Max Planck Institute, Heisenbergstrasse 1, Stuttgart 70569, Germany b Department of Physics, Trinity College Dublin, Dublin 2, Ireland Abstract A soluble form of narrow-gap polymer poly-tert-butyMsothionaphthalene (PTBITN) has been used in the formation of a Schottky diode with the rectifying contact occurring between PTBITN and the aluminium interface region. Indium-tin oxide (ITO) was used as the back transparent electrode and also served as an ohmic contact with the polymer. The device fabricated shows typical photoelectrical and photovoltaic characteristics. In addition, the optical response with regards to photovoltaic effects :firrors that of its absorption spectrum. Keywords: Poly-tert-butyl-isothionaphthalene; Photoconduction;Photovoltaic effects 1. Introduction In recent years extensive research has been carried out concerning the development of organic semiconductors util- izing their unique electronic and optoelectronic properties [ 1 ]. Investigations into polymers with unsaturated carbon double bonds that possess extended "rr electron systems have been studied for an insight into their basic interaction proc- esses such as electron-phonon and electron-electron states [2]. One of the most attractive properties of these materials is their photoconductive ability across a broad wavelength region of the spectrum. When dealing with polymers there are two dominating processes for conduction: the first is a hopping process which is transport between individual poly- mer strands, the second is band conduction which deals with transport along the polymer conjugated backbone via the ,rr states. The study of photovoltaic and light-emitting diodes has become an area of extensive research in recent years [3-8 ]. The material which has dominated interest in light emission is poly(phenylenevinylene) (PPV) and its wide range of derivatives [9-12]. Research into this family of polymers has shown that tuneable light emission is possible, ranging from blue to red [ 13-15]. Efficiencies of 2% and more have been achieved, which is extraordinary considering the break- through in this type of device was achieved only recently * Correspondingauthor. Fax: +49 711 689 1010;e-mail:curran@klizix. mpi.stuttgart.mpg.de. 0379-6779/96/$15.00 © 1996ElsevierScienceS.A. All rights reserved PIIS0379-6779(96)04486-4 [ 16]. Another area of interest is the relatively undeveloped subject of polymer photodetection. Although, at present, device efficiencies are quite low, the prospect of fabricating devices on a molecular scale is more realistic using short chain potymers or oligomers than for nanostructure scale inorganic devices. Most of the development in polymer elec- tronics has been done in the production of either p-n junctions or Schottky and metal-insulator-semiconductor diodes [ 17-20]. A Schottky barrier or metal semiconductor junction can be formed by depositing a low work function metal, such as Ca or A1, onto a p-type polymer. This creates a space charge region in the semiconductor, resulting in a rectifying contact. The barrier arises due to the existence of a contact potential between the metal and semiconductor. The motion of an electron and hole going from a semiconductor to a metal is governed by diffusion and drift. The current is primarily determined by whichever presents the greater resistance to current flow. Diffusion theory is applicable to low mobility carriers; the limitation of charge transfer is that which builds up at the barrier region. Thermionic emission theory governs the transport of carriers from semiconductor to metal so limits the current and is applicable to high mobility materials. When a metal and semiconductor come into contact an initial stable thermal equilibrium must be established. With differing workfunction metal contacts there are two cases that are possible. Firstly, no space charge build-up at the semi- conductor/metal interface will ensure an ohmic contact while, secondly, space charging results in minority carriers