Large area ultra-thin graphene films for functional photovoltaic devices
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ARTICLE Large area ultra-thin graphene films for functional photovoltaic devices Mallika Dasari and Matthew P. Hautzinger Department of Chemistry & Biochemistry, Southern Illinois University, Carbondale, Illinois 62901, USA
Haiyan Fan-Hagenstein Department of Chemistry, School of Science and Technology, Nazarbayev University, Astana 010000, Kazakhstan
Brice Adam Russell and Aldo D. Migone Department of Physics, Southern Illinois University, Carbondale, Illinois 62901, USA
Punit Kohlia) Department of Chemistry & Biochemistry, Southern Illinois University, Carbondale, Illinois 62901, USA (Received 22 January 2018; accepted 30 May 2018)
Graphene possesses exceptional mechanical, electrical, and thermal properties that stand out for numerous applications in materials and energy-related areas. The growing demand to produce high-quality large-scale graphene films inexpensively remains a challenge. The work presented in this paper emphasizes a straightforward method of producing high-quality graphene films using cellulose as the starting materials. We demonstrate the synthesis of defect-free graphene films (as thin as ;10 layers) on substrates up to 7 cm2 in area. Graphitic films were characterized using Infrared Raman, energy-dispersive X-ray spectroscopy, X-ray diffraction (XRD), scanning electron microcopy SEM, and high-resolution transmission electron microscopy (HRTEM). Our XRD, Raman, and HRTEM studies indicated that the synthetic temperature was critical in the synthesis of high-quality graphene films using cellulose as the carbon source material. Systematic studies revealed that defect-free large area graphitic films were produced at a synthetic temperature of ;900 °C. The Raman D band peak intensity decreased for the samples synthesized at higher temperature but was absent for the samples prepared at 900 °C. Both the HRTEM and selected area electron diffraction confirm the highly ordered arrangement of carbon atoms in the sample matrix. The measured distance between lattice fringes was 0.335 nm, which matches with the literature reported fringe distance for the high-quality graphene. The XRD spectrum of the thin graphitic samples synthesized at 900 °C displayed a sharp diffraction peak 2h–26.5° characteristic of highly crystalline defect-free graphene. Functional photodetector and photovoltaic (PV) devices were fabricated using graphitic films. The graphitic films were used as one of the electrodes for the PV devices yielded a power conversion efficiency of ;1%. Our synthetic method can be potentially used for producing high-quality free-standing graphene films inexpensively at large-scale.
I. INTRODUCTION
The two-dimensional carbon-based material graphene has remarkable electronic properties. It is a zero-gap semiconductor indicated by the valence and conduction band overlap at the Dirac points.1,2 Graphene’s outstanding charge mobility of ;10,000 cm1/s,3 thermal conductivity of ;4.84 103 to 5.30 103 W/mK,4 and mechanical strength of 42 N/m are of great interest for potential electronic, optical, and optoelectron
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