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Real Time Spectroscopic Ellipsometry (RTSE) Analysis of Three Stage CIGS Deposition by co-Evaporation

Pradhan, Puja
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1493344332238366

Abstract Details

2017, Doctor of Philosophy, University of Toledo, Physics.
Spectroscopic ellipsometry (SE) is a powerful tool to characterize multilayered thin films, providing structural parameters and materials optical properties over a wide spectral range. Further analyses of these optical properties can provide additional information of interest on the physical and chemical properties of materials. In-situ real time SE (RTSE) combines high surface sensitivity with fast data acquisition and non-destructive probing, thus lends insights into the dynamics of film growth. In this dissertation, the methods of SE have been applied to investigate the growth and properties of material components used in the CIGS thin film photovoltaic technology. Examples of RTSE data collection and analyses are demonstrated for the growth of selenium (Se), molybdenum diselenide (MoSe2) and copper selenide (Cu2-xSe), used in CIGS technology which can then be applied in complete analysis of three-stage CIGS deposition by co-evaporation. Thin film Mo deposited by sputtering is the most widely used back contact for solar cells using CIGS absorbers. In this study, in-situ and real time characterization have been utilized in order to investigate the growth as well as the structural, optical, and electronic properties of Mo thin films deposited by DC magnetron sputtering at different substrate temperatures. In these studies, the surface roughness on the Mo is observed to decrease with increasing substrate temperature. The growth rate, nucleation behavior, evolution of surface roughness and development of void structures in Mo show strong variations with deposition temperature. In depth analyses of (e1, e2) provide consistent estimates of void fraction, excited carrier mean free path, group speeds of excited carriers and intrinsic stress in the films. Complementary ex-situ characterization of the as deposited Mo films included XRD, resistivity measurements by four-point-probe, SEM, and profilometry. This dissertation describes the research performed on the (In1-xGax)2Se3 (IGS) thin films with different Ga composition (x) and different IGS bulk layer thicknesses. The (e1, e2) database for IGS was obtained at 400°C by RTSE starting from films deposited by co-evaporation from fluxes of In, Ga, and Se with different x as in the stage I of three-stage co-evaporation process. The goal of this study is to develop a dielectric function database of IGS films with different x, enabling composition monitoring and thickness control during IGS deposition. RTSE has also been applied successfully in this dissertation research for real time monitoring of Cu-poor to Cu-rich and Cu-rich to Cu-poor transitions during the growth of CIGS films by three-stage co-evaporation. RTSE analyses for all three stages of CIGS growth have been presented including new results for IGS-to-CIGS conversion throughout stage II, Cu2-xSe development at the end of stage II, and Cu2-xSe to CIGS conversion in stage III. Thus, it has been demonstrated that in-situ RTSE combines high thickness, phase, and compositional sensitivity with fast non-invasive data acquisition, thus providing unique insights into the dynamics of CIGS film growth. This non-destructive, high speed capability has the potential to supplement or replace existing monitoring techniques applied for multi-stage co-evaporation of CIGS in both laboratory and industry settings. For further insights into the effect of deposition temperature on device performance, a higher than standard substrate temperature was utilized for the growth of CIGS thin films. Elevation of the substrate temperature for stage II/III deposition from 570C to 620C has led to significant improvements in the efficiency of the CIGS solar cell. The highest efficiency CIGS solar cell obtained in this study is 17.4%.
Robert Collins (Committee Chair)
Nikolas J. Podraza (Committee Member)
Bo Gao (Committee Member)
Jacques G. Amar (Committee Member)
Dean M. Giolando (Committee Member)
377 p.
Materials Science; Physics; Solid State Physics
Spectroscopic Ellipsometry; RTSE; selenium; molybdenum diselenide; copper selenide; Molybdenum; dielectric function; three-stage Copper Indium Gallium di-selenide deposition by co-evaporation

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Citations

  • Pradhan, P. (2017). Real Time Spectroscopic Ellipsometry (RTSE) Analysis of Three Stage CIGS Deposition by co-Evaporation [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1493344332238366

    APA Style (7th edition)

  • Pradhan, Puja. Real Time Spectroscopic Ellipsometry (RTSE) Analysis of Three Stage CIGS Deposition by co-Evaporation . 2017. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1493344332238366.

    MLA Style (8th edition)

  • Pradhan, Puja. "Real Time Spectroscopic Ellipsometry (RTSE) Analysis of Three Stage CIGS Deposition by co-Evaporation ." Doctoral dissertation, University of Toledo, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1493344332238366

    Chicago Manual of Style (17th edition)

toledo1493344332238366
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This open access ETD is published by University of Toledo and OhioLINK.