Defects in Chalcopyrites - Advanced Characterisation - DECK
Coordinating Institution:
Université du Luxembourg
Contracting Partner(s):
University of Helsinki (Finland) ,
University of Warsaw
Other Partner(s):
Helmholtz-Zentrum, Berlin (D)
From: 01/09/2008
To: 31/08/2011
Budget: 250,000.00€
Contact(s):
Siebentritt Susanne
Progress Summary 2009
Chalcopyrite solar cells represent the most advanced technology for thin film photovoltaics. Despite the technological advancement many questions concerning their electronic defects are open. The physico-chemical nature of defects is not clear, although they are responsible for the doping which directly influences main figures of merit of the devices. Chalcopyrite solar cells show a number of metastabilities, causing problems in production.
An understanding of its correlation with defects is just beginning. The aim of the project is to contribute to a correlation between the electronic structure and the nature of defects and between defects and metastability. The project involves partners from Warsaw and Helsinki with specific expertise in different techniques of defect spectroscopy.
The Laboratory of Photovoltaics of the University of Luxembourg is providing the samples for all partners’ investigations. We use photoluminescence (PL) to characterise defects and the photovoltaic potential of the films. Single crystalline films are prepared by metal organic vapour phase epitaxy (MOVPE). The machine arrived in December 2008 and was taken into service in May 2009 – there were some delays because of problems with the installation. We started growing CuGaSe2 epitaxial films and have achieved high quality single crystalline films and excellent composition control, which is essential for our and the partners’ experiments. Meanwhile we have also achieved epitaxy of CuInSe2 with good results.
Samples were provided to the partners according to their requests. Our own investigations were originally aimed at a method called bias-PL which was supposed to give us information about deep defects, which are normally not accessible by PL. However, we did not succeed to obtain any meaningful signal from chalcopyrites. We can measure other semiconductors with this method, so it is not a fault of the set-up built within this project.
But neither CuGaSe2 nor CuInSe2 nor the alloy Cu(In,Ga)Se2, neither bulk crystals, nor epitaxial films, nor polycrystalline films did show any response. We have a few speculations why this is the case, but they don’t help us to understand the defects in chalcopyrites further. Therefore we have built a new set-up that allows us to measure the PL spatially resolved with a sub-micrometer resolution. The quantitative analysis of these spectra allows us to determine the local quality of the excited state in the absorber layers. Variations in that quality are critical for the efficiency of solar cells. Distinct variations were found in single crystalline films, though much smaller than in the best polycrystalline films.
Programme:
- ERA-Net MATERA, Call 2007
Foreign Funding Agency:
- AKA (Finland) ; MSHE (Poland)¨
Figure: The MOVPE machine has arrived in the new LPV labs.