8 July 2013

Solliance and imec achieve 9.7% efficiency with CZTSe thin-film solar cell

At the Intersolar North America 2013 conference in San Francisco, Belgium-based imomec (imec’s associated lab at Hasselt University) and Solliance (the European R&D consortium that focuses on thin-film photovoltaic solar energy) are presenting a 1cm x 1cm CZTSe (Cu2ZnSnSe4)-based solar cell with 9.7% efficiency (AM1.5G), for which certification is expected in October. The result is claimed to be a key step to bringing the solar industry closer to a sustainable alternative to 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). 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 that is suitable for a multi-junction, thin-film solar cell rivaling the efficiency of CIGS cells (about 20%). Imomec, imec and Solliance have defined a path towards further improving the layers and cell structures of CZTSe and CZTS absorbers, aimed at developing a multi-junction CZTS/CZTSe solar cell with 20% cell efficiency. The new CZTSe solar cell is a key step towards reaching this goal, it is reckoned.

Imec/imomec fabricated the CZTSe layers by sputtering copper (Cu), zinc (Zn) and tin (Sn) metal layers onto a molybdenum-on-glass substrate followed by subsequent annealing in an H2Se-containing atmosphere. 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 1cm x 1cm cell was 9.7%, with a maximum short-circuit current of 38.9mA/cm2, an open-circuit voltage of 0.41V and a fill factor of 61%.

“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,” says 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.”

The sputtering of the Cu, Zn and Sn layers was performed at Gent-based Flamac, a division of SIM vzw (Strategisch Initiatief Materialen in Vlaanderen, or Strategic Initiative Materials in Flanders), and the international glass manufacturer AGC delivered molybdenum-on- glass substrates. Imec’s thin-film solar cell activities at imomec are integrated in the Solliance cross-border collaboration platform, and the research was partially supported by the Flemish ‘Strategisch Initiatief Materialen’ (SIM) SoPPoM program.

See related items:

Imec and Flamac to co-develop new thin-film PV materials

IBM sets efficiency record for thin-film PV using earth-abundant materials

First PV cells from Solliance’s CIGS facility yield 13.85% efficiency

Tags: CIGS CZTS Thin-film PV

Visit: www.imec.be

Visit: www.uhasselt.be/IMO

Visit: www.solliance.eu