Solar Cell Contacts: Quantifying the Impact of Interfacial Layers on Charge Transfer, Selectivity, Recombination, and Open-Circuit Voltage

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dc.contributor.advisorLonergan, Mark
dc.contributor.authorEgelhofer Ruegger, Kira
dc.date.accessioned2020-12-08T16:10:57Z
dc.date.issued2020-12-08
dc.description.abstractSolar cells require two primary components to function: an absorber and contacts, either of which may limit photovoltaic efficiency. For example, the contacts of silicon and perovskite solar cells limit their performance. To increase efficiency, interfacial layers (IFLs) sandwiched between absorber and contact are frequently used. Improvements due to IFLs are often attributed to changes in qualitative ideas of selectivity and recombination. Further, IFL/contact properties are conflated with performance parameters that depend on the entire cell. While IFLs may improve efficiency, knowledge of their precise impact on electron and hole transfer at contacts and the relation of these effects to efficiency and well-defined concepts of selectivity and recombination is lacking, limiting photovoltaic technology development. This work addresses this gap by measuring both electron and hole transfer rates at IFL-modified contacts. Further, these rates are related to the open-circuit voltage, an important photovoltaic performance metric, and definitions of selectivity and recombination developed by our group. Specifically, the action of spiro-OMeTAD, the most common IFL used in perovskite solar cells, is characterized by making it a third contact to the interdigitated back-contact silicon solar cell. This architecture creates a three-in-one photovoltaic that, with numerical simulation, provides equilibrium exchange current densities for electrons (J0n) and holes (J0p) as quantitative charge transfer rates. We define contact selectivity as the ratio of the two J0 values at one contact (e.g., J0p/J0n) while (J0nJ0p)0.5 describes contact recombination. Compared to bare gold, adding spiro-OMeTAD reduces (J0nJ0p)0.5 by 104, passivating gold to recombination. Incorporating common dopants Li- and Co-TFSI and oxygen exposure increase J0p/J0n by up to 109. The improvement in Voc from using spiro-OMeTAD in these cells, however, is not directly due to these changes but rather to increased electron collection asymmetry between the two contacts. The effects of additive t-BP on the J0 values also lend insight into unique chemistry when Co-TFSI is used, likely influencing its effect on Voc. Further, operando measurements demonstrate the contribution of spiro-OMeTAD to broadly observed hysteresis behavior. These insights will aid the rational design of IFLs for improved photovoltaic efficiencies. This dissertation contains both published and unpublished co-authored work.en_US
dc.description.embargo2021-10-26
dc.identifier.urihttps://hdl.handle.net/1794/25918
dc.language.isoen_US
dc.publisherUniversity of Oregon
dc.rightsAll Rights Reserved.
dc.subjectCharge Transferen_US
dc.subjectInterfacial Layersen_US
dc.subjectOpen-Circuit Voltageen_US
dc.subjectPhotovoltaicsen_US
dc.subjectSelectivityen_US
dc.subjectSpiro-OMeTADen_US
dc.titleSolar Cell Contacts: Quantifying the Impact of Interfacial Layers on Charge Transfer, Selectivity, Recombination, and Open-Circuit Voltage
dc.typeElectronic Thesis or Dissertation
thesis.degree.disciplineDepartment of Chemistry and Biochemistry
thesis.degree.grantorUniversity of Oregon
thesis.degree.leveldoctoral
thesis.degree.namePh.D.

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