### Session B39: Focus Session: Materials and Applications for Solar Energy I

11:15 AM–2:03 PM, Monday, March 5, 2007

Chair: Mike McGehee, Stanford University

Abstract ID: BAPS.2007.MAR.B39.3

### Abstract: B39.00003 : Local Structures Around S in CdS:O Thin Films Photovoltaic Materials Probed by S K-edge X-ray Absorption Fine Structures

12:03 PM–12:15 PM

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#### Authors:

Y. L. Soo
W. H. Sun
S. C. Weng
Y. S. Lin
S. L. Chang
(National Tsing Hua University, Taiwan)

L. Y. Jang
(NSRRC, Taiwan)

X. Wu
Y. Yan
(NREL)

Local Structures around S in thin films of CdS:O have been investigated using EXAFS and NEXAFS techniques at the S K absorption edge. Our S K-edge EXAFS results clearly indicate the presence of S-O bonds that coexist with S-Cd bonds in the oxygen-containing samples. The S K-edge NEXAFS data further identify SO$_{3}$ and SO$_{4}$ complexes in the samples. As indicated by our previous results on Cd K-edge EXAFS, Cd atoms are predominantly bonded with S. These x-ray results demonstrate that the oxygen atoms actually combine with S to form SO$_{3}$ and SO$_{4}$ complexes instead of being incorporated into the CdS host. In combination with the evidence of nanoparticles revealed by TEM, our results suggest that oxygen-free CdS nanocrystals are formed in the films due to the O content. The bandgap of the samples is therefore found to increase with O concentration as opposed to the bandgap decrease for O doping expected in the band anticrossing model.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.MAR.B39.3