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Sulfurization of co-evaporated Cu2ZnSnSe4 thin film solar cells: The role of Na.

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Title: Sulfurization of co-evaporated Cu2ZnSnSe4 thin film solar cells: The role of Na.
Authors: de la Cueva, L.1 leonor.cueva@uam.es, Sánchez, Y.2, Calvo-Barrio, L.3, Oliva, F.2, Izquierdo-Roca, V.2, Khelifi, S.4,5, Bertram, T.6, Merino, J.M.1, León, M.1, Caballero, R.1 raquel.caballero@uam.es
Source: Solar Energy Materials & Solar Cells. Nov2018, Vol. 186, p115-123. 9p.
Subject Terms: *Solar cells, *Kesterite, Thin films, Tuned mass dampers, Photonic band gap structures
Abstract: The sulfurization of co-evaporated Cu 2 ZnSnSe 4 (CZTSe) thin films is studied. In this work, a relationship between the Na concentration and the further S incorporation in the CZTSe absorber layer is found. Na is added by a NaF precursor layer before CZTSe co-evaporation and/or by diffusion from the soda-lime glass s ubstrate. Higher Na concentrations result in bigger grain sizes, higher S/(S + Se) atomic ratios and photovoltaic devices with higher V OC, as investigated by SEM, GIXRD, Raman and I-V measurements. Results using an alternative substrate as ceramic verify the importance of the control of the Na content, which alters the carrier concentrations and elements distribution with much higher S and Na concentrations at the surface in this particular case. By using this methodology, it is possible to tune the kesterite band gap energy by the creation of S-gradient through the absorber thin film. This may provide a new approach for the control of Cu 2 ZnSn(S,Se) 4 growth and development of high efficiency kesterite solar cells. Efficiencies of 5.5% and 6.4% are obtained using ceramic and SLG substrates respectively (without antireflection coatings and without grids). [ABSTRACT FROM AUTHOR]
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Abstract:The sulfurization of co-evaporated Cu 2 ZnSnSe 4 (CZTSe) thin films is studied. In this work, a relationship between the Na concentration and the further S incorporation in the CZTSe absorber layer is found. Na is added by a NaF precursor layer before CZTSe co-evaporation and/or by diffusion from the soda-lime glass s ubstrate. Higher Na concentrations result in bigger grain sizes, higher S/(S + Se) atomic ratios and photovoltaic devices with higher V OC, as investigated by SEM, GIXRD, Raman and I-V measurements. Results using an alternative substrate as ceramic verify the importance of the control of the Na content, which alters the carrier concentrations and elements distribution with much higher S and Na concentrations at the surface in this particular case. By using this methodology, it is possible to tune the kesterite band gap energy by the creation of S-gradient through the absorber thin film. This may provide a new approach for the control of Cu 2 ZnSn(S,Se) 4 growth and development of high efficiency kesterite solar cells. Efficiencies of 5.5% and 6.4% are obtained using ceramic and SLG substrates respectively (without antireflection coatings and without grids). [ABSTRACT FROM AUTHOR]
ISSN:09270248
DOI:10.1016/j.solmat.2018.06.015