Organic Solar Cells with Graphene Electrodes and Vapor Printed Poly(3,4-ethylenedioxythiophene) as the Hole Transporting Layers
- 22 June 2012
- journal article
- Published by American Chemical Society (ACS) in ACS Nano
- Vol. 6 (7), 6370-6377
- https://doi.org/10.1021/nn301901v
Abstract
For the successful integration of graphene as a transparent conducting electrode in organic solar cells, proper energy level alignment at the interface between the graphene and the adjacent organic layer is critical. The role of a hole transporting layer (HTL) thus becomes more significant due to the generally lower work function of graphene compared to ITO. A commonly used HTL material with ITO anodes is poly(3,4-ethylenedioxythiophene) (PEDOT) with poly(styrenesulfonate) (PSS) as the solid-state dopant. However, graphene’s hydrophobic surface renders uniform coverage of PEDOT:PSS (aqueous solution) by spin-casting very challenging. Here, we introduce a novel, yet simple, vapor printing method for creating patterned HTL PEDOT layers directly onto the graphene surface. Vapor printing represents the implementation of shadow masking in combination with oxidative chemical vapor deposition (oCVD). The oCVD method was developed for the formation of blanket (i.e., unpatterened) layers of pure PEDOT (i.e., no PSS) with systematically variable work function. In the unmasked regions, vapor printing produces complete, uniform, smooth layers of pure PEDOT over graphene. Graphene electrodes were synthesized under low-pressure chemical vapor deposition (LPCVD) using a copper catalyst. The use of another electron donor material, tetraphenyldibenzoperiflanthene, instead of copper phthalocyanine in the organic solar cells also improves the power conversion efficiency. With the vapor printed HTL, the devices using graphene electrodes yield comparable performances to the ITO reference devices (ηp,LPCVD = 3.01%, and ηp,ITO = 3.20%).This publication has 26 references indexed in Scilit:
- Enhancing the conductivity of transparent graphene films via dopingNanotechnology, 2010
- Roll-to-roll production of 30-inch graphene films for transparent electrodesNature Nanotechnology, 2010
- Ultrahigh electron mobility in suspended grapheneSolid State Communications, 2008
- Large-area ultrathin films of reduced graphene oxide as a transparent and flexible electronic materialNature Nanotechnology, 2008
- Current-induced cleaning of grapheneApplied Physics Letters, 2007
- Electromechanical Resonators from Graphene SheetsScience, 2007
- Electronic Confinement and Coherence in Patterned Epitaxial GrapheneScience, 2006
- Two-dimensional atomic crystalsProceedings of the National Academy of Sciences of the United States of America, 2005
- Surface oxidation activates indium tin oxide for hole injectionJournal of Applied Physics, 2000
- Work function of indium tin oxide transparent conductor measured by photoelectron spectroscopyApplied Physics Letters, 1996