Transfer of Cu(In,Ga)Se2 thin film solar cells to flexible substrates using an in situ process control

Development and investigation of flexible thin film technologies are attracting increased attention in recent years. The translation of high efficiencies from rigid glass substrates to flexible substrate materials, scaling up the solar cell area and device optimisation on low-temperature substrates are all of crucial interest. Using Cu(In,Ga)Se-2 as absorber layer material deposited by co-evaporation with an in situ laser light scattering (LLS) process control, we have reached an efficiency of 16.7% (AM1.5) for laboratory scale cells on glass. This contribution reports on advances in performance optimisation, which have been achieved for single solar cells, produced on Ti-foil and polyimide substrates with a total area of up to 16 cm(2). The photovoltaic performance on Ti-substrates can be optimised through adjustment of the sodium content, resulting in an efficiency of 16.2% on laboratory scale devices. Thus, the transfer of the small area efficiency from glass to titanium foil as substrate material is basically accomplished and a device efficiency of 12.2% for a 16.5-cm(2) total area device on Ti-foil could be achieved. In order to process Cu(In,Ga)Se2 devices on the temperature-sensitive polyimide substrates, a trade off needs to be considered between low-process temperatures, which are still tolerable to the substrate, on the one hand and on the other hand high-process temperatures, which are necessary to ensure good device qualities. LLS proves to be a valuable tool to gauge a possible process temperature interval. Thus, on small areas of 0.5 cm2, in this work, devices on polyimide have reached an efficiency of 10.8%. (c) 2004 Elsevier B.V All rights reserved.