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We present a study on the performance and analysis of hybrid solar cells comprising a planar heterojunction between between a conjugated donor polymer, P3HT or PCPDTBT, and hydrogenated amorphous silicon (a-Si:H). A comparison of the modeled absorption spectra of the layer stack with the measured external quantum efciency is used to investigate the contribution of the inorganic and organic material to the photocurrent generation in the device. Although both materials contribute to the photocurrent, the devices exhibit poor quantum e ciencies and low short circuit currents. Bandstructure simulations of the hybrid layer structure reveal that an unfavorable electric eld distributionwithin the planarmultilayer structure limits the performance. Using electroabsorption measurements we can show that the electric eld is extremelyweak in the amorphous siliconbut strong in the organicmaterial. The situation changes drasticallywhen the conjugated polymer is p-doped. Doping not only increases the conductivity of the organic material, but also restores the electric eld in the amorphous silicon layer. Optimized hybrid solar cells comprising thin doped P3HT layers exhibit energy conversion e ciencies (ECE) up to 2.8 %. || S. Schaefer, S. Albrecht, D. Neher: Universitat Potsdam, Institute of Physics and Astronomy, Soft Matter Physics, D-14476 Potsdam, Germany T. F. Schulze, E. Conrad, L. Korte, B. Rech: Department of Silicon Photovoltaics, Helmholtz Center Berlin for Materials and Energy, Kekulestr. 5, D-12489 Berlin, Germany J. Wordenweber, A. Gordijn: IEK5-Photovoltaik, Forschungszentrum Julich, D-52425 Julich, Germany U. Scherf, I. Dumsch: Bergische Universitat Wuppertal, Macromolecular Chemistry and Institute for Polymer Technology, GaussStrasse 20, D-42097 Wuppertal, Germany

In this work, the authors present a 7.5% efficient hybrid tandem solar cell with the bottom cell made of amorphous silicon and a Si-PCPDTBT:PC70BM bulk heterojunction top cell. Loss-free recombination contacts were realized by combing Al-doped ZnO with either the conducting polymer composite PEDOT:PSS or with a bilayer of ultrathin Al and MoO3. Optimization of these contacts results in tandem cells with high fill factors of 70% and an open circuit voltage close to the sum of those of the sub-cells. This is the best efficiency reported for this type of hybrid tandem cell so far. Optical and electrical device modeling suggests that the efficiency can be increased to similar to 12% on combining a donor polymer with suitable absorption onset with PCBM. We also describe proof-of-principle studies employing light trapping in hybrid tandem solar cells, suggesting that this device architecture has the potential to achieve efficiencies well above 12%. (C) 2014 Elsevier B.V. All rights reserved.

Solution-based semiconductors give rise to the next generation of thin-film electronics. Solution-based silicon as a starting material is of particular interest because of its favorable properties, which are already vastly used in conventional electronics. Here, the application of a silicon precursor based on neopentasilane for the preparation of thin-film solar cells is reported for the first time, and, for the first time, a performance similar to conventional fabrication methods is demonstrated. Because three different functional layers, n-type contact layer, intrinsic absorber, and p-type contact layer, have to be stacked on top of each other, such a device is a very demanding benchmark test of performance of solution-based semiconductors. Complete amorphous silicon n-i-p solar cells with an efficiency of 3.5% are demonstrated, which significantly exceeds previously reported values.