Substrate based CdTe solar cells fabricated on metallic foils: Device, material, and processing issues

Substrate CdTe cells are uncommon due to the difficulty in forming effective contacts to p-type CdTe. The development of such solar cells could further increase the applications and enhance the product characteristics of the lowest cost thin film PV technology, by making lightweight and flexible products possible. This paper reviews the current status of the development of substrate CdTe solar cells on flexible metallic substrates. The influence of substrate impurities, the effect of impurity barrier layers, the effect of heat treatments, and the use of various compounds as back contacts are among the topics to be discussed. Presently the efficiency of foil/CdTe-type solar cells is in the 6.5% range. The performance is limited by low V_OC´s (<;700 mV) and the fact that the p-type contact to CdTe is rectifying leading to poor FFs.