Extensive Penetration of Evaporated Electrode Metals into Fullerene Films: Intercalated Metal Nanostructures and Influence on Device Architecture.
Although it is known that evaporated metals can penetrate into films of various organic molecules that are a few nanometers thick, there has been little work aimed at exploring the interaction of the common electrode metals used in devices with fullerene derivatives, such as organic photovoltaics (OPVs) or perovskite solar cells that use fullerenes as electron transport layers. In this paper, we show that when commonly used electrode metals (e.g., Au, Ag, Al, Ca, etc.) are evaporated onto films of fullerene derivatives (such as [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)), the metal penetrates many tens of nanometers into the fullerene layer. This penetration decreases the effective electrical thickness of fullerene-based sandwich structure devices, as measured by the device's geometric capacitance, and thus significantly alters the device physics. For the case of Au/PCBM, the metal penetrates a remarkable 70 nm into the fullerene, and we see penetration of similar magnitude in a wide variety of fullerene derivative/evaporated metal combinations. Moreover, using transmission electron microscopy to observed cross-sections of the films, we show that when gold is evaporated onto poly(3-hexylthiophene) (P3HT)/PCBM sequentially processed OPV quasi-bilayers, Au nanoparticles with diameters of ∼3-20 nm are formed and are dispersed entirely throughout the fullerene-rich overlayer. The plasmonic absorption and scattering from these nanoparticles are readily evident in the optical transmission spectrum, demonstrating that the interpenetrated metal significantly alters the optical properties of fullerene-rich active layers. This opens a number of possibilities in terms of contact engineering and light management so that metal penetration in devices that use fullerene derivatives could be used to advantage, making it critical that researchers are aware of the electronic and optical consequences of exposing fullerene-derivative films to evaporated electrode metals.
Department of Chemistry and Biochemistry, University of California, Los Angeles , Los Angeles, California 90095-1569, United States.
Guangye
G
Zhang
Department of Materials Science and Engineering, University of California, Los Angeles , Los Angeles, California 90095, United States.
Steven A
SA
Hawks
Department of Materials Science and Engineering, University of California, Los Angeles , Los Angeles, California 90095, United States.
Chilan
C
Ngo
Department of Chemistry and Biochemistry, University of California, Los Angeles , Los Angeles, California 90095-1569, United States.
Laura T
LT
Schelhas
Department of Chemistry and Biochemistry, University of California, Los Angeles , Los Angeles, California 90095-1569, United States.
D Tyler
DT
Scholes
Department of Chemistry and Biochemistry, University of California, Los Angeles , Los Angeles, California 90095-1569, United States.
Hyeyeon
H
Kang
Department of Chemistry and Biochemistry, University of California, Los Angeles , Los Angeles, California 90095-1569, United States.
Jordan C
JC
Aguirre
Department of Chemistry and Biochemistry, University of California, Los Angeles , Los Angeles, California 90095-1569, United States.|Department of Materials Science and Engineering, University of California, Los Angeles , Los Angeles, California 90095, United States.|California NanoSystems Institute, University of California, Los Angeles , Los Angeles, California 90095, United States.
Sarah H
SH
Tolbert
Department of Chemistry and Biochemistry, University of California, Los Angeles , Los Angeles, California 90095-1569, United States.|California NanoSystems Institute, University of California, Los Angeles , Los Angeles, California 90095, United States.
Benjamin J
BJ
Schwartz
D004560:Electricity; D004563:Electrochemistry / Q000295:instrumentation*; D004566:Electrodes; D004952:Esters / Q000737:chemistry; D037741:Fullerenes / Q000737:chemistry*; D008670:Metals / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D012666:Semiconductors; D014835:Volatilization
D004952:Esters; D037741:Fullerenes; D008670:Metals
PCBM; conjugated polymer; fullerene; gold nanoparticles; metal penetration; organic photovoltaic; plasmonics; sequential processing