2017 Participants
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NAME: Deben Shoup

Modification of Zinc Oxide Nanoparticles with Fluorinated Phosphonic Acids

Zinc oxide (ZnO) nanoparticles have semiconductive properties that can be modified to increase the performance and efficiency of solar cells. ZnO nanoparticles are inexpensive and abundant, making them ideal for use as an electron transfer layer in the structure of inverted solar cells. A relatively simple and cost efficient method of surface modification is forming self-assembled monolayers (SAMs) onto the surface of ZnO via adsorption.  SAMs can greatly alter the physical and chemical properties of ZnO to make it more suitable for a wide variety of applications. The formation of perfluorinated phosphonic acids are being utilized for this project due to the highly electronegative nature of fluorine. Specifically, 12-pentafluorophenoxydodecyl phosphonic acid, 2,3,4,5,6-pentafluorobenzyl phosphonic acid, and (1H,1H,2H,2H-Heptadecafluorodec-1-yl)phosphonic acid have been used to form thin films on the ZnO nanoparticle surfaces. Fourier transform infrared spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy have been used to analyze and characterize the modified nanoparticles and determine the effects that each of the different phosphonic acids have on the ZnO.  The perfluorinated phosphonic acid SAMs have formed strong chemically bonded films on the ZnO, and the work functions of the modified ZnO nanoparticles have been tuned due to the dipoles in the C-F bonds. The work function was found to be higher than that of unmodified ZnO which is crucial for its inclusion in inverted solar cells.