Reactive magnetron sputtering of precursors for CZTS solar cells
2012 (English)Conference paper, Presentation (Refereed)
At the moment, CIGS (CuInGaSe2) solar cells show the highest efficiency among industrial scale produced thin film solar cells. Given the present strong increase in production, however, the availability and price of indium will become an issue because of its low abundance in Earth's crust. Therefore, there is strong interest in alternative indium free absorber materials. Kesterites CZTS (Cu2ZnSn(SxSe1-x)4) attracted most attention owing to the fact that relatively high efficiencies have already been demonstrated and also due to the similarity to CIGS. In this contribution we report on reactive sputtering for deposition of CZTS precursors. In order to avoid Sn loss at elevated temperatures a two stage process, synthesis of precursor films at relatively low substrate temperature followed by annealing, is used. Depositions are performed by pulsed DC magnetron sputtering from two targets, a CuSn alloy and Zn, in a mixture of Ar and H2S. The film structure is evaluated by X-ray diffraction and Raman spectroscopy while the composition is analysed by RBS, XRF, EDS and EPMA. Internal stress is measured by deflection of thin substrates. Characteristics of the deposition process are discussed with respect to the discharge power, total pressure, substrate temperature and H2S flow on the film structure and composition.
Sulphur incorporation can be readily controlled by H2S flow with the structure changing from amorphous to columnar with increasing S content. The main issue encountered in the depositions is related to the film composition as the ratio between Cu and Sn does not correspond to the target composition. This effect is discussed in detail with respect to the sputtering and transport through the gas phase. Finally, material properties after annealing are briefly summarized.
Place, publisher, year, edition, pages
Manufacturing, Surface and Joining Technology
Research subject Engineering Science with specialization in Electronics
IdentifiersURN: urn:nbn:se:uu:diva-190008OAI: oai:DiVA.org:uu-190008DiVA: diva2:582795
ICMCTF 2012, 39th International Conference on Metalurgical Coatings and Thin Films, April 2012, San Diego, CA USA