Magnetron Sputtering for Low-temperature Deposition of CdTe-based Photovoltaics
- PDF / 787,528 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 208 Views
B3.7.1
Magnetron sputtering for low-temperature deposition of CdTe-based photovoltaics Alvin D. Compaan Department of Physics and Astronomy, The University of Toledo, Toledo, OH 43606, USA ABSTRACT Although the deposition over large areas of polycrystalline thin-film semiconductors such as CdTe is possible by a variety of methods including close spaced sublimation, vapor transport deposition, physical vapor deposition, organometallic chemical vapor deposition, and electrodeposition, the use of a plasma-based method such as magnetron sputtering can have significant advantages. In this paper I review recent results from our group in the fabrication of CdS/CdTe cells using rf magnetron sputtering and discuss some of the advantages that appear possible from the use of sputtering methods in this class of materials. Some of these advantages are particularly relevant as the polycrystalline thin-film community address issues related to the challenges of fabricating high efficiency tandem cells with efficiencies over 25%. Recently we have achieved: improvements in sputtered cell performance with cells based on commercial SnO2:F as well as on substrates with our own sputtered ZnO:Al, progress in the use of reactive sputtering for the deposition of oxygen alloys of CdS and N-doped layers of ZnTe, and progress in the sputtering of wider and narrower bandgap alloys of CdTe with Zn, Mn, and Hg. Details of the sputtering process and some of the recent achievements are discussed below.
RECENT RESULTS FOR SPUTTERED CELLS We have previously reported sputtered cells with efficiency up to 11.6% on soda-lime glass with a commercial coating of SnO2:F.1 This substrate material is known to have limitations in transparency and has less than optimum texture. Nevertheless, a good supply of substrate material is readily available and convenient and most of our effort has been based on this starting material. Recently we have made slight adjustments in our process and have improved the cell performance to 12.6% as measured at NREL. The current-voltage and quantum efficiency results are shown in Fig.1. To make these improvements we have reduced slightly the thickness of the sputtered CdS layer and etched off the CdS prior to soldering an In buss line for the negative contact. The final structure of the cell is: 2 mm soda lime glass/0.5µm SnO2:F/0.13µm CdS/2.3µm CdTe/3nm Cu/20nm Au. Prior to the application of the back contact, the cell structure receives a vapor CdCl2 treatment at 387 oC for 30 minutes in one atmosphere of dry air as described in our Final Technical Report for 1994-8.2 There is no wet chemical treatment/etch or water rinse at any point in the fabrication process after the cleaning of the TEC-15 glass substrate. It is well known that the use of a highly resistive transparent (HRT) interfacial layer between the transparent conducting oxide (TCO) and the CdS allows cells to be fabricated with a thinner CdS layer and an improved blue response greater than the roughly 30% QE shown in Fig. 1 for the region between 350 and 550 nm. We
Data Loading...
