Programm Photovoltaik Ausgabe 2008 ... - Bundesamt für Energie BFE

3/6
The Athlet consortium comprises 23 partners from 11 EU countries, including 7 industrial partners,
research centres and academic institutions. Athlet is coordinated by HMI Berlin (D). Three Swiss partners
are participating: The University of Neuchâtel (IMT) which is coordinating SP IV (SP IV) while
also participating in SP I, Oerlikon which is also participating in SP IV and the ETH Zurich (Prof. A.
Tiwari) is participating in SP I and III.
Results
Small area thin-film silicon cells
Cell development on small area cell was also performed in the framework of an OFEN project. The
main deliverables for the Athlet projects for 2007 were the following:
1. Micromorph tandem cell with intermediate reflector with a open-circuit voltage �1.4 V
2. Micromorph tandem cell with a stable short-circuit current of �13 mA/cm 2
3. Micromorph tandem cell with a stable efficiency of �12%
The first deliverable was achieved in June 07. Micromorph tandems (with SiOx based intermediate
reflectors) with more than 13 mA/cm 2 and 12% initial performance were very recently fabricated. Stable
values of the short-circuit and efficiency is not yet known. However, assuming known degradation
figures and the deposition of a front ant-reflective coating, these cells should satisfy the the defined
deliverables targets. More details on the results are presented in the report of the OFEN project.
Large area thin-film silicon cells
The up-scaling path from small area reactor to the large area KAI 1200 reactor of Oerlikon (1.4 m 2 )
goes through 2 intermediate sizes, i.e. the KAI-S (35x45 cm 2 electrode size, work done at IMT) and
KAI-M (45x55 cm 2 electrode size, work done at Oerlikon and also now at IMT).
Main deliverables for IMT on 30x30 cm 2 was the fabrication of micromorph test cell (1 cm 2 ) with intermediate
reflector with > 10% efficiency as well as the fabrication of micromorph test cell deposited at
least 10 Å/s with �9% initial efficiency.
In order to attain the 10% efficiency, it was necessary to improve the amorphous cell to be used as top
cell in the micromorph tandem cell. Especially fill-factor and short circuit current needed to be improved.
By optimizing doped and intrinsic layers a significant increase in both parameters was
achieved: The new state of the art cell efficiency in KAI-S reactor is now >10% and the best cell
reached 10.5% initial efficiency on 0.25 cm 2 cell surface. The other cell parameters are: Voc= 888 mV,
FF= 75.4%, Jsc= 15.65 mA/cm 2 . The I(V) characteristics are shown in Fig. 2.
Current density (mA/cm 2 )
20
15
10
5
0
-5
-150 0 150 300 450 600 750 900
Voltage (mV)
Fig. 2: IV curve of amorphous silicon solar cell in KAI-S system at IMT. Initial best cell efficiency for
250 nm thickness is 10.5%.
ATHLET, N. Wyrsch, IMT Seite 57 von 288