Vapour deposited solar cells based on CuPc-C60 single heterojunction:: optimization of the deposition process

We present the photovoltaic characteristics improvement of vapour deposited solar cells based on single p-n heterojunction CuPc-C-60 active bilayer and achieved with subsequent CuPc and. C-60 evaporation with a home-made co-evaporation setup including an in situ top aluminium contact evaporation cell. First a thickness optimisation of the active layer is presented in regard of I(V) characteristics under a 4 mW/cm(2) low level illumination. We obtain the best results with a C-60 layer thickness little more important than related in literature and we attributed this result to the lacunar behaviour of the C-60 layer. These devices present very low fill factors that have been attributed to the sample transfer in open air prior the Al top contact deposition. Using our new co-evaporation setup with an in situ Al evaporation cell, we have obtained solar cells with a fill factor twice improved. The feature is attributed to the great improvement of the C-60/Al interface, resulting in a dramatic reduction of the series resistance of the equivalent circuit diagram of the solar cell. However, the photovoltaic characteristics of these devices slowly degrades when the light intensity increase from 4 mW/cm(2) to near one sun (100 mW/cm(2)) AM 1.5 illumination. (C) 2004 Elsevier B.V. All rights reserved.