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Uppsala, Sweden

Scragg J.J.,Angstrom Solar Center | Dale P.J.,University of Luxembourg | Colombara D.,University of Bath | Peter L.M.,University of Bath
ChemPhysChem | Year: 2012

A simple and useful thermodynamic approach to the prediction of reactions taking place during thermal treatment of layers of multinary semiconductor compounds on different substrates has been developed. The method, which uses the extensive information for the possible binary compounds to assess the stability of multinary phases, is illustrated with the examples of Cu(In,Ga)Se 2 and Cu 2ZnSnSe 4 as well as other less-studied ternary and quaternary semiconductors that have the potential for use as absorbers in photovoltaic devices. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Ericson T.,Angstrom Solar Center | Scragg J.J.,Angstrom Solar Center | Hultqvist A.,Angstrom Solar Center | Hultqvist A.,Stanford University | And 4 more authors.
IEEE Journal of Photovoltaics | Year: 2014

To improve the conduction band alignment and explore the influence of the buffer-absorber interface, we here investigate an alternative buffer for Cu 2 ZnSnS4 (CZTS) solar cells. The Zn(O, S) system was chosen since the optimum conduction band alignment with CZTS is predicted to be achievable, by varying oxygen to sulfur ratio. Several sulfur to oxygen ratios were evaluated to find an appropriate conduction band offset. There is a clear trend in open-circuit voltage (Voc), with the highest values for the most sulfur rich buffer, before going to the blocking ZnS, whereas the fill factor peaks at a lower S content. The best alternative buffer cell in this series had an efficiency of 4.6% and the best CdS reference gave 7.3%. Extrapolating Voc values to 0 K gave activation energies well below the expected bandgap of 1.5 eV for CZTS, which indicate that recombination at the interface is dominating. However, it is clear that the values are affected by the change of buffer composition and that increasing sulfur content of the Zn(O, S) increases the activation energy for recombination. A series with varying CdS buffer thickness showed the expected behavior for short wavelengths in quantum efficiency measurements but the final variation in efficiency was small. © 2013 IEEE. Source

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