title: Boosting Photon Harvesting in Organic Solar Cells with Highly Oriented Molecular Crystals via Graphene-Organic Heterointerface.
abstract: Photon harvesting in organic solar cells is highly dependent on the anisotropic nature of the optoelectronic properties of photoactive materials. Here, we demonstrate an efficient approach to dramatically enhance photon harvesting in planar heterojunction solar cells by using a graphene-organic heterointerface. A large area, residue-free monolayer graphene is inserted at anode interface to serve as an atomically thin epitaxial template for growing highly orientated pentacene crystals with lying-down orientation. This anisotropic orientation enhances the overall optoelectronic properties, including light absorption, charge carrier lifetime, interfacial energetics, and especially the exciton diffusion length. Spectroscopic and crystallographic analysis reveal that the lying-down orientation persists until a thickness of 110 nm, which, along with increased exciton diffusion length up to nearly 100 nm, allows the device optimum thickness to be doubled to yield significantly enhanced light absorption within the photoactive layers. The resultant photovoltaic performance shows simultaneous increment in Voc, Jsc, and FF, and consequently a 5 times increment in the maximum power conversion efficiency than the equivalent devices without a graphene layer. The present findings indicate that controlling organic-graphene heterointerface could provide a design strategy of organic solar cell architecture for boosting photon harvesting.
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology , Pohang 790-784, Korea.
authors.forename: Sae Byeok
authors.initials: SB
authors.lastname: Jo
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology , Pohang 790-784, Korea.
authors.forename: Hyun Ho
authors.initials: HH
authors.lastname: Kim
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology , Pohang 790-784, Korea.
authors.forename: Hansol
authors.initials: H
authors.lastname: Lee
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology , Pohang 790-784, Korea.
authors.forename: Boseok
authors.initials: B
authors.lastname: Kang
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology , Pohang 790-784, Korea.
authors.forename: Seongkyu
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology , Pohang 790-784, Korea.
authors.forename: Myungsun
authors.initials: M
authors.lastname: Sim
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology , Pohang 790-784, Korea.
authors.forename: Min
authors.initials: M
authors.lastname: Kim
authors.affiliation: Department of Organic and Nano System Engineering, Konkuk University , Seoul 143-701, Korea.
authors.forename: Wi Hyoung
authors.initials: WH
authors.lastname: Lee
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology , Pohang 790-784, Korea.
authors.forename: Kilwon
authors.initials: K
authors.lastname: Cho
keywords: epitaxial growth; graphene; heterointerface; molecular orientation; organic solar cells; planar heterojunction