Transparent films on polymers for photovoltaic applications

Highly conductive and transparent tin-doped indium oxide (ITO) films have been prepared by RF sputtering processes on polymer substrates, polyethylene terepthalate (PET) and polyimide (Kapton KJ((R))), and onto glass as reference. The utilisation of a RF plasma pre-treatment of the organic substrate surface leads to the realisation of adherent films on unheated substrates with good optoelectronic properties and without damage to the polymers. High transparency, near 80% on the 400-1100 nm spectra range, and conductivity, sigma > 10(3) (Omega cm)(-1), have been achieved for ITO films deposited onto PET and Kapton KJ((R)) substrates. These are adequate values for the utilisation of these modified polymer samples as substrates for photovoltaic solar cells. Better optical and electrical properties of the ITO films have been observed when deposited on polymer foils if compared with those deposited on glass. Improved quality of ITO samples have been correlated with the growth of more oriented and crystalline ITO films along the preferred orientation <100>. The ITO films fabricated on polymers by the method proposed do not require substrate heating during the film preparation or any post-deposition annealing treatment in order to achieve the optoelectronic quality required. (C) 2002 Elsevier Science Ltd. All rights reserved.