Investigation on nanostructured solar cells

Kang, Hyun Min

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https://hdl.handle.net/2142/34567 Copy

Description

Title

Investigation on nanostructured solar cells

Author(s)

Kang, Hyun Min

Issue Date

2012-09-18T21:25:56Z

Director of Research (if dissertation) or Advisor (if thesis)

Kim, Kyekyoon

Doctoral Committee Chair(s)

Kim, Kyekyoon

Committee Member(s)

• Choi, Hyungsoo
• Krein, Philip T.
• Wasserman, Daniel M.

Department of Study

Electrical & Computer Eng

Discipline

Electrical & Computer Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• nanostructured solar cells
• quantum dot solar cells
• tin sulfide(SnS)
• cadmium sulfide(CdS)
• cadmium selenide(CdSe)
• zinc oxide(ZnO) nanowire
• flow-limited field-injection electrostatic spraying (FFESS)
• flame pyrolysis FFESS

Abstract

In this study, materials for the nanostructured solar cells were synthesized and their effects were investigated. TiO2 nanoparticles, which are commonly used in the nanostructured solar cells, were synthesized by a newly developed technique, combining the advantages of flame aerosol synthesis and flow-limited field-injection electrostatic spraying (FFESS). The new method provides good stability and reproducibility, demonstrating the generation of TiO2 nanoparticles with more flexibility in the control of their properties. The charged droplet size controlled by FFESS is the key variable because it determines the ratio of vapor to liquid phase reactions taking place in the flame. The small anatase nanoparticles were mainly formed through vapor reactions and the large anatase and rutile nanoparticles through liquid-phase reactions. The rutile phase increased with the droplet size. The number of charged droplets mainly affects the TiO2 nanoparticle size rather than the phase. CdS and CdSe layers were deposited on the TiO2 network prepared from thus-synthesized TiO2 nanoparticles and their effects on the performance of solar cells were investigated. A CdS underlayer was beneficial for the solar cells in all respects because it increased light absorption by promoting the CdSe absorber growth, increased resistance against recombination by forming a physical barrier and passivating the interface, and improved electron injection and transport. It is important to increase the amount of electrons in the TiO2 nanoparticle network in the nanostructured solar cells, which requires an increase in the light absorption, electron injection and collection. To increase the light absorption, the quantity of absorber is to be maximized, which can be achieved by optimizing the thickness of the absorber layer, the TiO2 particle size, and network thickness. The optimum values are determined primarily by the saturation point of the light absorption. The additional thickness or size of the absorber and TiO2 beyond the saturation of light absorption is not desirable because the electron injection and/or transfer is degraded. To promote electron injection in the TiO2 network, it is necessary to increase the conduction band level of the absorber, in order to reduce trap sites at the interface and to increase the screening effect of electrons by the electrolyte. Finally, to increase electron collection, fast electron transport and longer lifetime are required, which can be attained by surface area optimization, by minimizing recombination, and by reducing trap sites.

Graduation Semester

2012-08

Permalink

http://hdl.handle.net/2142/34567

Copyright and License Information

Copyright 2012 Hyun Min Kang

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