Both CdTe and Cu(In,Ga)Se2 have produced highly efficient thin film solar cells, exceeding 22% in champion devices. Both are also manufactured in large scales and show promise as future energy technologies. However, understanding the current collection mechanisms and mechanisms of instability in the devices remain a concern. To address these questions, we have used scanning probe and photoemission spectroscopies to study the response of chalcogenide materials to light and how charge is collected. Results of scanning microwave impedance microscopy and conductive atomic force microscopy show dramatic differences in the behavior of CdTe and Cu(In,Ga)Se2 (CIGS). The results include characterization of the effect of CdCl2 treatment on the properties CdTe grains and grain boundaries. This treatment dramatically increases the current collection in the grain boundaries. Thus we show that CdTe solar cells operate apparently by generation of electron hole pairs in the CdTe grains and collection of electrons to the grain boundaries. By contrast, CIGS grains show little or no contrast between the grains and grain boundaries and no obvious conduction pathway through the grain boundaries appears to exist. Our surface analysis results are supplemented with other measurements of both surface and bulk microchemistry and microstructure.
Angus A. Rockett, "Surface analysis of chalcogenide semiconductors used in photovoltaics (Conference Presentation)," Proc. SPIE 10099, Physics, Simulation, and Photonic Engineering of Photovoltaic Devices VI, 100990O (Presented at SPIE OPTO: January 31, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2256914.5390916519001.
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