2026-09-20T19:43:31Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/1067722021-07-05T14:03:20Zcom_1721.1_7582com_1721.1_7581col_1721.1_131023
Rafael Jaramillo.
Yin, Han, Ph.D. Massachusetts Institute of Technology
Massachusetts Institute of Technology. Department of Mechanical Engineering.
Massachusetts Institute of Technology. Department of Mechanical Engineering
2017-01-30T19:17:38Z
2017-01-30T19:17:38Z
2016
2016
http://hdl.handle.net/1721.1/106772
969904913
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 60-67).
Persistent photoconductivity (PPC) has been observed in numerous semiconductors and dielectrics. It refers to the phenomenon that photoconductivity can last for a long time after photo-excitation is terminated. In most cases, the causes of PPC are unknown, and the connections between synthesis conditions, composition, morphology, and PPC are unexplored. Here, we study the effect of chemical bath deposition parameters on PPC in CdS thin films, including bath temperature, concentration of reactants, deposition time, stirring speed and cation source. By tuning the chemical conditions during deposition, we achieved near stoichiometric CdS thin films exhibiting large photoconductive responses (up to 109 times conductivity increase in simulated solar light compared to the dark) that persist for a long time (decay time constant up to 10 hours) after illumination is turned off. We offer experimental support for the hypothesis that sulfur vacancies are responsible for PPC in CdS, and we discuss the role of trap states in PPC are discussed. We also discuss the implications of giant and persistent photoconductivity for thin film solar cells in which CdS is used as the n-type buffer layer.
by Han Yin.
S.M.
67 pages
eng
Massachusetts Institute of Technology
MIT theses are protected by copyright. They may be viewed, downloaded, or printed from this source but further reproduction or distribution in any format is prohibited without written permission.
http://dspace.mit.edu/handle/1721.1/7582
Mechanical Engineering.
Effect of synthesis conditions on large and persistent photoconductivity in chemical bath deposited cadmium sulfide thin films
PPC in CdS thin films
Thesis
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<Abstract>Persistent photoconductivity (PPC) has been observed in numerous semiconductors and dielectrics. It refers to the phenomenon that photoconductivity can last for a long time after photo-excitation is terminated. In most cases, the causes of PPC are unknown, and the connections between synthesis conditions, composition, morphology, and PPC are unexplored. Here, we study the effect of chemical bath deposition parameters on PPC in CdS thin films, including bath temperature, concentration of reactants, deposition time, stirring speed and cation source. By tuning the chemical conditions during deposition, we achieved near stoichiometric CdS thin films exhibiting large photoconductive responses (up to 109 times conductivity increase in simulated solar light compared to the dark) that persist for a long time (decay time constant up to 10 hours) after illumination is turned off. We offer experimental support for the hypothesis that sulfur vacancies are responsible for PPC in CdS, and we discuss the role of trap states in PPC are discussed. We also discuss the implications of giant and persistent photoconductivity for thin film solar cells in which CdS is used as the n-type buffer layer.</Abstract>
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