CdTe/CdS solar cells on flexible substrates Xavier Mathew a, * , J. Pantoja Enriquez a , Alessandro Romeo b,c Ayodhya N. Tiwari b,d a Centro de Investigacion en Energia-UNAM, 62580, Temixco, Morelos, Mexico b Thin Film Physics Group, Laboratory for Solid State Physics, ETH (Swiss Federal Institute of Technology) Zurich, Technopark, ETH-Building, Technoparkstr. 1, CH-8005 Zurich, Switzerland c UniversitaÕ di Verona, CaÕVignal 2, Strada Delle Grazie, 37134 Verona, Italy d Centre for Renewable Energy Systems and Technology, Department of Electronic and Electrical Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK Received 9 March 2004; received in revised form 8 June 2004; accepted 8 June 2004 Available online 23 August 2004 Communicated by: Associate Editor T.M. Razykov Abstract The development of CdTe/CdS solar cells on flexible substrates is reviewed in this article. Photovoltaic structures on lightweight and flexible substrates have several advantages over the heavy glass based structures in both terrestrial and space applications. The cells mounted on flexible foil are not fragile, the requirements of the supporting structures are minimum and they can be wrapped onto any suitably oriented or curved structures. The specific power of the solar cells is an important factor in space applications and hence development of photovoltaic devices on light weight substrates is interesting. CdTe is one of the leading candidates for photovoltaic applications due to its optimum band gap for the efficient photo-conversion and robustness for industrial production with a variety of film preparation methods. Flexible solar cells with conversion efficiencies exceeding 11% have been developed on polyimide foils. The development of CdTe devices on metallic substrates is impeded due to the lack of a proper ohmic contact between CdTe and the substrate. The polymer substrate has the advantage that the devices can be prepared in both ‘‘superstrate’’ and ‘‘substrate’’ configurations. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: CdTe solar cell; Flexible substrate; Close spaced sublimation 1. Introduction Solar energy is one of the abundant, non-polluting renewable energy of our planet. During the last three decades considerable progress has been made in devel- oping technologies to harness electricity from solar radi- ation. The most commonly used solar cell material is crystalline silicon (Si) and naturally the cost is an obsta- cle to terrestrial applications. In the last two decades considerable work has been done in developing thin film solar cells to replace the costly single crystal and wafer based solar cells and the progress achieved is encouraging. 0038-092X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.solener.2004.06.020 * Corresponding author. Fax: +52 777 3250018. E-mail addresses: xm@cie.unam.mx (X. Mathew), alessan- dro.romeo@univr.it (A. Romeo), a.n.tiwari@lboro.ac.uk (A.N. Tiwari). Solar Energy 77 (2004) 831–838 www.elsevier.com/locate/solener