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Impact of deep traps on CIGS solar cell performance and reliability

Paul, Pran Krishna
http://rave.ohiolink.edu/etdc/view?acc_num=osu1555287435800404

Abstract Details

2019, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Thin-film polycrystalline Cu(In,Ga)Se2 (CIGS) based photovoltaic has the potential to reach significant market share in the terrestrial solar area due to its high optical absorption, tunable bandgap, low cost of deposition, flexibility and high material stability. Despite these advantages, CIGS conversion efficiency is still about two-thirds of the Shockley-Queisser limit due, at least in part, to crystalline defects and related carrier traps. CIGS films contain different grain boundaries, crystalline orientations, and phases which create many intrinsic and extrinsic traps/energy levels throughout the bandgap. Deep traps in CIGS not only cause the initial solar cell efficiency loss but are also responsible for instabilities (temporary and recoverable changes in the solar cell parameters such as efficiency) and degradation (permanent changes) induced by exposure to light, heat, and moisture. To improve the efficiency and reliability of CIGS-based solar cells it is necessary to reduce the number of traps; knowledge of the spatial and energetic distribution of traps, and identification of their physical sources, are thus very important. To achieve these objectives, this dissertation applied a unique set of characterization techniques: notably deep level transient/optical spectroscopes, scanning deep level transient spectroscopy, fast capacitance voltage, external quantum efficiency (EQE), and lighted current-voltage measurement. A model is proposed to explain the mechanism of light and heat induced instabilities/degradation in CIGS solar cells. The values in the model are informed by experiment including defect spectroscopies. It has been shown that the presence and concentration of two deep levels at midgap and close to the conduction band (EV+0.98 eV) can predict the change of the light, heat, moisture induced instabilities/degradation of the open circuit voltage (VOC), short circuit current (JSC), fill factor (FF) of the CIGS solar cell. This suggests that minimizing the concentrations of both the midgap and EV+0.98 eV levels will be necessary to mitigate light, heat induced instabilities/degradation in CIGS solar cells. Through this comprehensive understanding of the role of deep traps in CIGS performance and reliability, high performance reliable CIGS based photovoltaic device can be achieved through better growth processes and design strategies.
Aaron Arehart, Professor (Advisor)
Tyler Grassman, Professor (Committee Member)
Hongping Zhao, Professor (Committee Member)
185 p.
Electrical Engineering

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Citations

  • Paul, P. K. (2019). Impact of deep traps on CIGS solar cell performance and reliability [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555287435800404

    APA Style (7th edition)

  • Paul, Pran Krishna. Impact of deep traps on CIGS solar cell performance and reliability. 2019. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1555287435800404.

    MLA Style (8th edition)

  • Paul, Pran Krishna. "Impact of deep traps on CIGS solar cell performance and reliability." Doctoral dissertation, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555287435800404

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.