Soft X-ray characterization of Zn 1-xSn xO y electronic structure for thin film photovoltaics

Mukes Kapilashrami, Coleman X. Kronawitter, Tobias Törndahl, Johan Lindahl, Adam Hultqvist, Wei Cheng Wang, Ching Lin Chang, Samuel S. Mao, Jinghua Guo

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Zinc tin oxide (Zn 1-xSn xO y) has been proposed as an alternative buffer layer material to the toxic, and light narrow-bandgap CdS layer in CuIn 1-x,Ga xSe 2 thin film solar cell modules. In this present study, synchrotron-based soft X-ray absorption and emission spectroscopies have been employed to probe the densities of states of intrinsic ZnO, Zn 1-xSn xO y and SnO x thin films grown by atomic layer deposition. A distinct variation in the bandgap is observed with increasing Sn concentration, which has been confirmed independently by combined ellipsometry-reflectometry measurements. These data correlate directly to the open circuit potentials of corresponding solar cells, indicating that the buffer layer composition is associated with a modification of the band discontinuity at the CIGS interface. Resonantly excited emission spectra, which express the admixture of unoccupied O 2p with Zn 3d, 4s, and 4p states, reveal a strong suppression in the hybridization between the O 2p conduction band and the Zn 3d valence band with increasing Sn concentration.

Original languageBritish English
Pages (from-to)10154-10159
Number of pages6
JournalPhysical Chemistry Chemical Physics
Issue number29
StatePublished - 7 Aug 2012


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