Carbon Nanostructure Based Electrodes for High Efficiency Dye Sensitize Solar Cell

Authors

Santanu Das, Florida International UniversityFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Materials Science and Engineering

First Advisor's Name

Wonbong Choi

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Norman D. H. Munroe

Third Advisor's Name

Jiuhua Chen

Fourth Advisor's Name

Nezih Pala

Keywords

Graphene, Raman Spectroscopy, functionalization, Electrocatalytic, work function, fermi level, solar cells, graphene-CNT hybrid

Date of Defense

6-14-2012

Abstract

Synthesis and functionalization of large-area graphene and its structural, electrical and electrochemical properties has been investigated. First, the graphene films, grown by thermal chemical vapor deposition (CVD), contain three to five atomic layers of graphene, as confirmed by Raman spectroscopy and high-resolution transmission electron microscopy. Furthermore, the graphene film is treated with CF₄ reactive-ion plasma to dope fluorine ions into graphene lattice as confirmed by X-ray photoelectron spectroscopy (XPS) and UV-photoemission spectroscopy (UPS). Electrochemical characterization reveals that the catalytic activity of graphene for iodine reduction enhanced with increasing plasma treatment time, which is attributed to increase in catalytic sites of graphene for charge transfer. The fluorinated graphene is characterized as a counter-electrode (CE) in a dye-sensitized solar cell (DSSC) which shows ~ 2.56% photon to electron conversion efficiency with ~11 mAcm⁻² current density. Second, the large scale graphene film is covalently functionalized with HNO₃ for high efficiency electro-catalytic electrode for DSSC. The XPS and UPS confirm the covalent attachment of C-OH, C(O)OH and NO₃^- moieties with carbon atoms through sp²-sp³ hybridization and Fermi level shift of graphene occurs under different doping concentrations, respectively. Finally, CoS-implanted graphene (G-CoS) film was prepared using CVD followed by SILAR method. The G-CoS electro-catalytic electrodes are characterized in a DSSC CE and is found to be highly electro-catalytic towards iodine reduction with low charge transfer resistance (R_ct ~5.05 Wcm²) and high exchange current density (J₀~2.50 mAcm^-2). The improved performance compared to the pristine graphene is attributed to the increased number of active catalytic sites of G-CoS and highly conducting path of graphene.

We also studied the synthesis and characterization of graphene-carbon nanotube (CNT) hybrid film consisting of graphene supported by vertical CNTs on a Si substrate. The hybrid film is inverted and transferred to flexible substrates for its application in flexible electronics, demonstrating a distinguishable variation of electrical conductivity for both tension and compression. Furthermore, both turn-on field and total emission current was found to depend strongly on the bending radius of the film and were found to vary in ranges of 0.8 – 3.1 V/μm and 4.2 – 0.4 mA, respectively.

Identifier

FI12073001

Recommended Citation

Das, Santanu, "Carbon Nanostructure Based Electrodes for High Efficiency Dye Sensitize Solar Cell" (2012). FIU Electronic Theses and Dissertations. 678.
https://digitalcommons.fiu.edu/etd/678