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Novel CZTSe Solar Cell Hits 9.7% Efficiency

Unlike CIGS, CZTS and CZTSe do not suffer from abundancy issues. Under certain conditions, the CZTS and CZTSe bandgaps make a combined material system that are ideal for a multi-junction, thin-film solar cell that rivals the efficiency of CIGS cells
At next week’s Intersolar conference in San Francisco, imomec, imec’s associated lab at the Hasselt University, and Solliance will present a CZTSe (Cu2ZnSnSe4)-based solar cell with 9.7 percent efficiency.

Solliance. is the European R&D consortium that focuses on thin-film photovoltaic solar energy (PV),

The cell itself measured 1 x 1 cm2 and was measured at AM1.5G conditions.

'AM' refers to the air mass coefficient - the direct optical path length through the Earth's atmosphere, expressed as a ratio relative to the path length vertically upwards. The air mass coefficient can be used to help characterise the solar spectrum after solar radiation has travelled through the atmosphere. It is used to characterise the performance of solar cells under standard conditions, with AM1.5G being almost universal when characterising terrestrial power-generating panels.

This promising result is an important step bringing the solar industry closer to a sustainable alternative for the highest efficiency thin-film solar cells in production, based on CIGS ( which refers to CuInGaSe2 or CuInGaS2).

CZTSe is an emerging alternative solar cell absorber in thin-film solar cells, similar to CZTS (Cu2ZnSnS4).



Thin-film CZTSe solar cell achieving 9.7 percent efficiency

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 copper (Cu), zinc (Zn) and tin (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 1 x 1cm2 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, as illustrated in the graph below.



“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," 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 to help bringing to market sustainable energy sources."

The sputtering of the copper, zinc and tin 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.



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