New Thin-Film CZTSe Solar Cells Achieve 9.7% Efficiency

4th July 2013

IMEC

ES Admin

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imec and Solliance will present a CZTSe (Cu2ZnSnSe4)-based solar cell with 9.7 percent efficiency (1x1cm2, AM1.5G) at next week’s Intersolar conference in San Francisco. This result is very promising and will be an important step in bringing the solar industry closer to a sustainable alternative for the highest efficiency thin-film solar cells in production, based on CIGS (Cu(In,Ga)(S,Se)2).

CZTSe is an emerging alternative solar cell absorber in thin-film solar cells, similar to CZTS (Cu2ZnSnS4), which do not suffer from abundancy issues as CIGS does. Their bandgaps (at 1.5-1.6eV for CZTS, and 0.9eV for CZTSe) make a combined material system ideal for a multi-junction, thin-film solar cell that rivals the efficiency of CIGS cells (about 20 percent).

Aiming at developing a multi junction CZTS/CZTSe solar cell with 20 percent cell efficiency, imec and Solliance have defined a path towards further improving the layers and cell structures of CZTSe and CZTS absorbers. The presented CZTSe solar cell is an important step forward to reach this goal.

Imec 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.

Featuring a typical grain size of about 1µm, the resulting polycrystalline absorber layers are only 1µm thick. The samples were processed at Helmholtz Zentrum Berlin into solar cells using a standard process flow for thin film solar cells. They were then finished with a metal grid and anti-reflective coating at imec. The highest efficiency obtained on a 1x1cm2 cell was 9.7 percent, with an open circuit voltage of 0.41V, a fill factor of 61 percent, and a maximum short circuit current of 38.9mA/cm2.

Marc Meuris, program manager Solliance of the alternative thin-film PV program, commented: “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. 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 AGC delivered the 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’ SoPPoM program.