Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 5, Issue 18, Pages 9224-9240Publisher
AMER CHEMICAL SOC
DOI: 10.1021/am4030609
Keywords
self-assembled monolayer; organic photovoltaics; heterogeneous electron transfer rate constant; work function; open circuit voltage; power conversion efficiency
Funding
- Argonne-Northwestern Solar Energy Research (ANSER) Center, an Energy Frontier Research Center
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0001059]
- U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences [DE-AC02-06CH11357, DE-FG02-08ER46536]
- NSF
- MRSEC [DMR-1121262]
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [1121262] Funding Source: National Science Foundation
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With the goal of investigating and enhancing anode performance in bulk-heterojunction (BHJ) organic photovoltaic (OPV) cells, the glass/tin-doped indium oxide (ITO) anodes are modified with a series of robust silane-tethered bis(fluoroaryl)amines to form self-assembled interfacial layers (IFLs). The modified ITO anodes are characterized by contact angle measurements, X-ray reflectivity, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, grazing incidence X-ray diffraction, atomic force microscopy, and cyclic voltammetry. These techniques reveal the presence of hydrophobic amorphous monolayers of 6.68 to 9.76 angstrom thickness, and modified anode work functions ranging from 4.66 to 5.27 eV. Two series of glass/ITO/IFL/active layer/LiF/Al BHJ OPVs are fabricated with the active layer = poly(3-hexylthiophene):phenyl-C-71-butyric acid methyl ester (P3HT:PC71BM) or poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)-carbonyl]-thi-eno[3,4-b]thiophenediyl]]:phenyl-C-71-butyric acid methyl ester (PTB7:PC71BM). OPV analysis under AM 1.5G conditions reveals significant performance enhancement versus unmodified glass/ITO anodes. Strong positive correlations between the electrochemically derived heterogeneous electron transport rate constants (k(s)) and the device open circuit voltage (V-oc), short circuit current (J(sc)), hence OPV power conversion efficiency (PCE), are observed for these modified anodes. Furthermore, the strong functional dependence of the device response on k(s) increases as greater densities of charge carriers are generated in the BHJ OPV active layer, and is attributable to enhanced anode carrier extraction in the case of high-k(s) IFLs.
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