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Cu₂O Heterojunction Photovoltaics


Tolstova, Yulia (2016) Cu₂O Heterojunction Photovoltaics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z92V2D22.


Cuprous oxide (Cu2O) is an earth abundant semiconductor that has several promising photovoltaic properties, including high absorption in the visible range, high minority carrier diffusion length, and high majority carrier mobility. Cu2O can be easily synthesized by oxidation of copper foils in air. One important advantage that makes Cu2O highly relevant to today's solar cell markets dominated by crystalline silicon is its wide bandgap of 1.9 eV at room temperature, which makes it an ideal candidate for a top cell in tandem with a crystalline silicon bottom cell. The detailed balance efficiency of such a device exceeds 44%. In this work we aim to understand and address several issues that have limited Cu2O solar cell efficiency. We address the intrinsic p-type nature and chemical instability of Cu2O by pairing it with an appropriate n-type heterojunction partner Zn(O,S), which allows us to achieve devices with open circuit voltages exceeding 1 V. We identify presence of a current blocking layer and reduce it, which results in more than doubling the short circuit current to exceed 5 mA/cm2. Light beam induced current measurements highlight some of the issues inherent to polycrystalline Cu2O solar cells, including grain dependent collection and current losses due to presence of grain boundaries. In order to address the issues affecting Cu2O made by thermal oxidation we also develop thin film growth of Cu2O by molecular beam epitaxy on several substrates including MgO and heteroepitaxial noble metal templates that act as ohmic back contacts. These studies culminate in achievement of the first Cu2O/Zn(O,S) solar cells incorporating an absorber layer grown by molecular beam epitaxy.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:photovoltaics; earth-abundant materials; thin film deposition
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Atwater, Harry Albert
Thesis Committee:
  • Atwater, Harry Albert (chair)
  • Greer, Julia R.
  • Johnson, William Lewis
  • Minnich, Austin J.
Defense Date:27 May 2016
Record Number:CaltechTHESIS:06012016-163813213
Persistent URL:
Related URLs:
URLURL TypeDescription ItemArticle: Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering ItemArticle: Single phase, single orientation Cu2O (1 0 0) and (1 1 0) thin films grown by plasma-assisted molecular beam epitaxy ItemConf. P:aper: Molecular Beam Epitaxy of Cu2O Heterostructures for Photovoltaics ItemArticle: Interface stoichiometry control to improve device voltage and modify band alignment in ZnO/Cu2O heterojunction solar cells
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9820
Deposited By: Yulia Tolstova
Deposited On:04 Jun 2016 00:44
Last Modified:08 Nov 2023 00:12

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