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ITO-free inverted polymer solar cells with ZnO:Al cathodes and stable top anodes

: Sio, A. de; Chakanga, K.; Sergeev, O.; Maydell, K. von; Parisi, J.; Hauff, E. von


Solar energy materials and solar cells 98 (2012), pp.52-56
ISSN: 0927-0248
Journal Article
Fraunhofer ISE ()

We report on the application of ZnO:Al as the transparent conductive oxide in high performance inverted polymer solar cells. We show that the optimized inverted architecture, which does not contain low work function metals or water-based transport layers, can be employed without sacrificing device efficiency. The widely studied P3HT:PCBM donor-acceptor system was chosen for the active layer. ZnO:Al layers were produced by dc-magnetron sputtering on glass substrates and used as the cathode. The thickness of ZnO:Al was optimized to achieve a low sheet resistance while maintaining high transmission. The resulting ZnO:Al layers were smoother than the reference ITO samples, and the active layers could be processed directly onto ZnO:Al without employing additional buffer layers. The structure of the top anodic contact was also optimized. Initial devices with an Au layer demonstrated poor results, and device performance improved when a MoO3/Ag anode was used. Control devices i n the standard forward structure using commercial ITO coated glass substrates were compared to the ZnO:Al based cells. Higher photocurrents were obtained in the inverted structures than in the ITO-based solar cells due to the higher transmittance of ZnO:Al in the spectral range where the blend absorbs.