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Local Imaging of Optoelectronic Prop...

Cox, Phillip Alexander.

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Local Imaging of Optoelectronic Properties and Film Degradation in Polymer/Fullerene Solar Cells with Electrostatic Force Microscopy.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Local Imaging of Optoelectronic Properties and Film Degradation in Polymer/Fullerene Solar Cells with Electrostatic Force Microscopy./
作者:	Cox, Phillip Alexander.
面頁冊數:	102 p.
附註:	Source: Dissertation Abstracts International, Volume: 77-08(E), Section: B.
Contained By:	Dissertation Abstracts International77-08B(E).
標題:	Physical chemistry. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10077320
ISBN:	9781339588094

Local Imaging of Optoelectronic Properties and Film Degradation in Polymer/Fullerene Solar Cells with Electrostatic Force Microscopy.
Cox, Phillip Alexander.

Local Imaging of Optoelectronic Properties and Film Degradation in Polymer/Fullerene Solar Cells with Electrostatic Force Microscopy. - 102 p.

Source: Dissertation Abstracts International, Volume: 77-08(E), Section: B.

Thesis (Ph.D.)--University of Washington, 2016.

With power conversion efficiencies on the rise, organic photovoltaics (OPVs) hold promise as a next-generation thin-film solar technology. However, both device performance and stability are inextricably linked to local film structure. Methods capable of probing nanoscale electronic properties as a function of film structure are thus a crucial component of the rational design of efficient and robust devices. This dissertation describes the use of three scanning probe methods for studying local charge generation and photodegradation in polymer/fullerene solar cells. First, we show that time-resolved electrostatic force microscopy (trEFM) is capable of resolving local photocurrent from sub-bandgap excitation down to attoampere level currents, a result unattainable by traditional contact-mode methods. We find that the local charging rates measured with trEFM are proportional to external quantum efficiency (EQE) measurements made on completed devices, making trEFM images equivalent to local EQE maps across the entire solar spectrum. For both phase-segregated and well-mixed MDMO-PPV:PCBM film morphologies, we show that the local distribution of photocurrent is invariant to excitation wavelength, providing local evidence for the controversial result that the probability of generating separated charge carriers does not depend on whether excitons are formed at the singlet state or charge transfer state. Next, we describe how local dissipation imaging can be performed with commercially-available frequency-modulated electrostatic force microscopy (FM-EFM) and show that dissipation maps are highly sensitive to photo-oxidative effects in organic semiconductors. We show that photo-oxidation induced changes in cantilever energy dissipation are proportional to device performance losses. We further develop dissipation imaging by implementing ringdown imaging, which directly measures the quality factor of the cantilever, enabling quantitative dissipation mapping. Using organic photovoltaic materials as a testbed, we study macroscopic device degradation as a function of photooxidation for three different film morphologies. According to EQE measurements, we find that the stability of the macroscopic devices is very sensitive to processing conditions, with films processed with the solvent additive 1,8-diiodooctane being the most stable. At the microscopic level, we compare the evolution of cantilever power dissipation as a function of photochemical degradation for three different polymer/fullerene blend morphologies, and show that the evolution of local power dissipation correlates with device stability. Lastly, we show that cantilever power dissipation increases more rapidly over large fullerene aggregates than in well-mixed polymer/fullerene regions, suggesting that local photochemistry on the fullerene contributes strongly to the dissipation signal.

ISBN: 9781339588094Subjects--Topical Terms:

1981412
Physical chemistry.

Local Imaging of Optoelectronic Properties and Film Degradation in Polymer/Fullerene Solar Cells with Electrostatic Force Microscopy.
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