Browsing by Author "Rockett, A. A."

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    Characterization of cuInSe2/CdS thin-film photovoltaics by x-ray photoelectron spectroscopy
    (Lognor, 2016) Aydogan, Pinar; Johnson, N.; Rockett, A. A.; Suzer, Sefik
    CuInSe2/CdS are promising photovoltaic materials due to their low production costs, chemical flexibility, and their acceptable conversion efficiencies. Although basic understanding of the device performance in terms of charge collection and recombination mechanism(s) are identified, there is still room for better understanding the effects of various defects and imperfections on device performance. X-Ray Photoelectron Spectroscopy has long been utilized for investigating nature of the chemical and physical parameters effecting the performance of these materials and devices made out of them. One particular advantage of XPS is its ability to identify and quantify charge accumulation and/or depletion through analysis of the shifts in the binding energy of the elemental peaks as a result of the local electrical potentials developed, since the kinetic energy of the photoelectrons emitted is directly influenced by them. This work focuses on measuring the photoshifts individually for Cd, In and Cu via illumination by lasers with three different colors towards assessing the presence and the effect of atomic defects and/or imperfections.
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    XPS investigation of a CdS-Based photoresistor under working conditions: operando − XPS
    (American Chemical Society, 2012) Sezen, H.; Rockett, A. A.; Süzer, Şefik
    A noncontact chemical and electrical measurement X-ray photoelectron spectroscopy (XPS) technique is performed to investigate a CdS-based photoresistor during its operation. The main objective of the technique is to trace chemical- and location-specified surface potential variations as shifts of the XPS Cd 3d5/2 peak position without and under photoillumination with four different lasers. The system is also modeled to extract electrical information. By analyzing the measured potential variations with this model, locationdependent resistance values are represented (i) two dimensionally for line scans and (ii) three dimensionally for areal measurements. In both cases, one of the dimensions is the binding energy. The main advantage of the technique is its ability to assess an element-specific surface electrical potential of a device under operation based on the energy deviation of core level peaks in surface domains. Detection of the variations in electrical potentials and especially their responses to the energy of the illuminating source in operando, is also shown to be capable of detecting, locating, and identifying the chemical nature of structural and other types of defects.