EFFECT OF POST-PECVD PHOTO-ASSISTED ANNEAL ON MULTICRYSTALLINE SILICON SOLAR-CELLS

Silicon nitride (SiNx) films deposited by plasma enhanced chemical vap or deposition (PECVD) contain large amount of atomic hydrogen which ca n be driven into bulk silicon by post-PECVD anneal. The objective of t his paper is to understand and quantify the effects of the anneal on m ulticrystalline silicon (me-Si) solar cells. Detailed cell analysis an d model calculations are performed to assess the impact of the anneal on me-Si cells. Simple n(+)-p-p(+) solar cells with PECVD SiNx/SiO2 an tireflection (AR) coating are annealed in the temperature range of 350 degrees C to 700 degrees C. The efficiency of the cells made on EFG s ilicon increases by 45% due to the AR coating and then additional 25% due to the anneal. A trade off between short and long wavelength respo nse is found during the anneal. Low temperature anneal increases the s hort wavelength response, while high temperature anneal improves the l ong wavelength response at the expense of the short wavelength respons e. It is shown that the increase in short wavelength response is due t o improved surface passivation, and the decease in short wavelength re sponse after high temperature anneals is the result of the increase in short wavelength absorption in the SIN, film. Higher quality HEM sili con cells do not show appreciable increase in the long wavelength resp onse at higher anneal temperatures. Thus post-PECVD low temperature an neal helps all me-Si cells, but the effect of high temperature anneal is material specific. Cells made from materials which do not respond t o hydrogenation can degrade at high temperature anneal.