期刊
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
卷 4, 期 23, 页码 4038-4044出版社
AMER CHEMICAL SOC
DOI: 10.1021/jz4021525
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- Center for Interface Science: Solar-Electric Materials (CIS:SEM), an Energy Frontier Research Center
- U.S. Department of Energy, Office of Basic Energy Sciences [DE-SC0001084]
- National Defense Science and Engineering Graduate Fellowship program
- NSF graduate research fellowship [DGE-0644493]
- Department of Energy Office of Science Graduate Fellowship Program (DOE SCGF) [DE-AC05-06OR23100]
- NSF [DMR-1215753]
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [1215753] Funding Source: National Science Foundation
We use dipolar phosphonic acid self-assembled monolayers (PA SAMs) to modify the work function of the hole-extracting contact in polymer/fullerene bulk heterojunction solar cells. We observe a linear dependence of the open-circuit voltage (V-OC) of these organic photovoltaic devices on the modified indium tin oxide (ITO) work function when using a donor polymer with a deep-lying ionization energy. With specific SAMs, we can obtain V-OC values exceeding those obtained with the common poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) hole-extraction layer. We measure charge-carrier lifetimes and densities using transient photovoltage and charge extraction in a series of devices with SAM-modified contacts. As expected, these measurements show systematically longer carrier lifetimes in devices with higher V-OC values; however, the trends provide useful distinctions between different hypotheses of how transient photovoltage decays might be controlled by surface chemistry. We interpret our results as being consistent with changes in the band bending at the ITO/bulk heterojunction interface that have the net result of altering the internal electric field to help prevent electrons in fullerene domains from undergoing surface recombination at the hole-extracting electrode.
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