Solar Energy Materials 13 (1986) 307-318 307 North-Holland, Amsterdam SPRAY CdS-POLYACETYLENE THIN FILMS PHOTOVOLTAIC HETEROJUNCTIONS M. ABD-LEFDIL t), M. CADENE t), M. ROLLAND I), j. BOUGNOT 2) and M.J.M. ABADIE 3) l) Groupe de Dynamique des Phases Condensbes (L.A. 233), Universitb des Sciences et Techniques du Languedoc, 34060 Montpellier Cbdex, France e) Centre d'Electronique de Montpellier, Universitb des Sciences et Techniques du Languedoc, 34060 Montpellier Cbdex, France -~) Laboratoire d'Etudes des Mat~riaux Polymbres, Universitb des Sciences et Techniques du Languedoc, 34060 Montpellier Cbdex, France Received 5 November 1985 We made thin films photovohaic cells by a direct polymerisation of (CH)x onto a sprayed CdS layer. Electrical and optical characteristics of this device were measured, both with undoped (CH)~ (p-n heterojunctions) and heavily doped (CH)x (Schottky diode). In spite of its low efficiency such a junction would lead, after improvement, to very cheap photovoltaic cells. 1. Introduction Since the synthesis by Shirakawa et al. [1] of large area free standing films of polyacetylene, a strong interest was focused on this cheap material. It may be doped by a number of chemical species such as 12, AsF s, H2SO 4, ... (p-type), or Li, Na, K (n-type). Doping increases its electrical conductivity by more than twelve orders of magnitude (from 10 -9 up to 10 +3 (~ cm)-t). At low doping level, (CH)x has a semiconducting behaviour and reaches a quasi metallic state when heavily doped. On the other hand, the (CH)x optical properties are also of strong interest as it appears as a direct gap semiconductor with an optical bandgap lying from 1.5 eV (trans stable isomer) to 1.8 eV (cis isomer), which is well matched to the solar spectrum. At last, its absorptivity around the gap increases above l0 s cm-1. Concerning the field of energy storage or production, many works deal with electrochemistry to build up batteries [2,3]; photoelectrochemical cells [4], photo- voltaic devices, both p-n heterojunctions [5-7], and Schottky devices [8-10]. Our goal is to build up very low cost solar cells even if the efficiency remains weak. Consequently, we chose the spray technique to obtain thin polycrystalline CdS layers. These cells have been characterised by SEM and by their electrical and optical behaviour, studied under dark and illuminated conditions. 0165-1633/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)