Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE

Introduction / project objectives
Polycrystalline thin film Cu(In,Ga)Se2 (CIGS) solar cells are important because of very high efficiency,
long term stable performance, and their potential for low cost generation of solar electricity. The
National Renewable Energy Laboratory, USA has reported a world record efficiency of 20% for the
CIGS solar cells grown on glass substrates and several groups including ETHZ have achieved
efficiencies exceeding 17% on glass substrates.
The objectives of the work packages, we are involved in the collaborative project, include:
� Development of high efficiency lightweight and flexible CIGS solar cells on polymer foils and
improvement in processes for highest record efficiencies.
� Development of alternative processes towards simple and low cost manufacturing of high
efficiency flexible solar cells.
� Development of critical cell components of CIGS tandem solar cells for next generation of more
efficient solar cells.
� Development of a new spray technology incorporating ultrasonic fine and condensed mist
forming for alternative buffer layers
During 2008 the research focus was placed on the following topics:
Flexible CIGS cells with PVD grown In2S3 buffer
� Transfer of knowledge gain from PVD grown In2S3 on rigid glass substrates towards the
processing of flexible cells on polyimide foils with In2S3 buffer layer.
� Comparison of first results of PVD grown In2S3 buffer on flexible cells with that on of a CdS
reference cell.
Ultrasonic spray pyrolysis (USP)
� Development of new buffer layer deposition techniques based on ultrasonic fine and condensed
mist forming spray technique.
� Investigations of microstructure and inter-diffusion characteristics of most promising buffer
layers.
� Comparison of the ultrasonic sprayed buffers on Cu(In,Ga)(S,Se)2 and Cu(In,Ga)Se2 absorbers.
CuIn1-xGaxSe2 Photovoltaic Devices for Tandem Solar Cell Application
� Continuation of the work on CIGS solar cells on transparent conducting oxides (TCO) for tandem
solar cell applications.
� Processing of CIGS layers with different [Ga]/[In+Ga] ratios and characterisation of cell
parameters and layer morphology.
Some of the research activities described in this report were also partly suported from projects from
Swiss National funding agencies (BFE, CCEM).
Work and results
1) Flexible CIGS cells with PVD grown In2S3 buffer layer
In the previous period calibration experiments on glass substrates have been performed. We
investigated In2S3 powder of different suppliers and identified the source material, which gave best
results. The chemical composition, microstructure, homogeneity and transparency of deposited layer
were characterised depending on different processing parameters. Best efficiencies of CIGS cells
grown on SLG and with PVD grown buffer layer are around at 80% of the CdS reference cell.
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ATHLET - Advanced Thin Film Technologies for Cost Effective Photovoltaics, A. N. Tiwari, ETH Zürich
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