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Observing electron extraction by monolayer graphene using time-resolved surface photoresponse measurements
Lushuai Zhang1, Susmit Singha Roy1, Caroline R English1
1†Department of Materials Science and Engineering and §Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
ACS Nano
|March 10, 2015
Summary
Bare graphene can function as an efficient electron acceptor in organic photovoltaic devices (OPVs). This study reveals p-doped graphene acts as a cathode, improving device performance by extracting electrons from photoexcited organic materials.
Area of Science:
- Materials Science
- Organic Electronics
- Photovoltaics
Background:
- Graphene is a promising alternative to indium tin oxide (ITO) for organic photovoltaic devices (OPVs).
- However, achieving comparable performance with graphene electrodes, especially bare graphene, remains a challenge.
- Understanding graphene's interfacial behavior is crucial for optimizing OPV design.
Purpose of the Study:
- To investigate the charge extraction properties of bare p-doped graphene in organic photovoltaic devices.
- To elucidate the reasons behind the limited performance of graphene-based OPVs.
- To provide experimental insights for designing future graphene-electrode OPVs.
Main Methods:
- Time-resolved surface photoresponse measurements on pentacene-on-graphene films.
- Fabrication and characterization of graphene/pentacene/MoO3 and graphene/pentacene/C60 heterojunctions.
- Analysis of exciton dissociation and charge extraction mechanisms.
Main Results:
- P-doped monolayer graphene efficiently extracts electrons, not holes, from photoexcited pentacene.
- A graphene/pentacene/MoO3 device showed a significant surface photoresponse, indicating efficient exciton dissociation.
- Competing electron extraction by both graphene and C60 in a graphene/pentacene/C60 device led to a poor photoresponse.
Conclusions:
- P-doped graphene functions as an effective electron extraction layer in OPVs.
- Graphene is best utilized as a cathode in organic photovoltaic devices.
- These findings offer crucial guidance for the development of advanced graphene-based organic solar cells.
