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Solliance and imec achieve 9.7% efficiency with new thin-film CZTSe solar cell
CZTSe is an emerging alternative solar cell absorber in thin-film solar cells, similar to CZTS (Cu2ZnSnS4). Unlike CIGS, CZTS and CZTSe do not suffer from abundancy issues. At 1.5-1.6eV for CZTS, and 0.9eV for CZTSe, their bandgaps make a combined material system ideal for a multi-junction, thin-film solar cell that rivals the efficiency of CIGS cells (about 20 percent). Imomec, imec and Solliance have defined a path towards further improving the layers and cell structures of CZTSe and CZTS absorbers aiming at developing a multi junction CZTS/CZTSe solar cell with 20 percent cell efficiency. The presented CZTSe solar cell is an important step forward to reach this goal.
Imec/imomec fabricated the CZTSe layers by sputtering Cu, Zn and Sn metal layers on a Molybdenum-on-glass substrate and subsequent annealing in an H2Se containing atmosphere, achieving 9.7 percent efficiency. The resulting polycrystalline absorber layers are only 1µm thick, with a typical grain size of about 1µm. The samples were then processed at Helmholtz Zentrum Berlin into solar cells using a standard process flow for thin film solar cells and finished with a metal grid and anti-reflective coating at imec. The highest efficiency obtained on a 1x1cm2 cell was 9.7 percent, with a maximum short circuit current of 38.9mA/cm2, an open circuit voltage of 0.41V and a fill factor of 61 percent.
"This is a big win for us. We've been working toward this milestone since 2011 when we first started our research on alternative materials for thin-film photovoltaics at imec/imomec," said Marc Meuris, program manager Solliance of the alternative thin-film PV program. "Our efficiencies are the highest in Europe and approaching the world record for this type of thin-film solar cells, and we look forward to further advancing R&D to help bringing to market sustainable energy sources."
The sputtering of the Cu, Zn, Sn layers was performed at Flamac (Gent), and the international glass manufacturer AGC delivered Molybdenum-on- glass substrates. Imec's thin-film solar cell activities at imomec (imec's associated laboratory at the university of Hasselt) are integrated in the Solliance cross-border collaboration platform, and the research was partially supported by the Flemish 'Strategisch Initiatief Materialen' (SIM) SoPPoM program.
*certification expected in October 2013.
Imomec is the associated lab of imec at the Hasselt University (Belgium). Together with imo, the research institute of Hasselt University, it forms the Institute of Materials Research, imo-imomec. The core competences of imo-imomec are the development and characterization of new material systems with potential use in microelectronics, bioelectronics and nanotechnology. Particular attention is paid to novel organic and inorganic photovoltaic materials, advanced electro-optical and morphological characterization and reliability of novel generation solar cells including CZTSe, OPV, hybrid solar cells and printable solar cells. The lab counts more than120 people. Further information on imo-imomec can be found on www.uhasselt.be/IMO.
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