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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Electrical Engineering and Computer Science

First Advisor

Venkat Bommisetty


Organic bulk heterojunction solar cells use polymer thin film technology which is cost effective, flexible and easily processable. P3HT:PCBM bulk heterojunction solar cell is most widely studied organic solar cell. Solvent additives have been shown to enhance power conversion efficiency, but its effect on stability is yet to be explored in detail. In this thesis the influence of 1,8-diiodooctane (DIO) additive, on the stability, performance and morphology of conjugated polymer (P3HT)/fullerene (PCBM) based solar cells was studied. In organic bulk heterojunction solar cells the majority of light is absorbed in the donor material. The incident photons are converted to excitons which get separated into holes and electrons at a donor/acceptor interface. Donor/acceptor regions can be optimized using techniques such as thermal annealing and solvent additives. Diiodooctane (DIO) solvent, 0%, 3% and 4% by vol., was added into a P3HT:PCBM blend during fabrication of the cells. The device structure used for this study was ITO/ PEDOT:PSS/ P3HT:PCBM/ Ca/ Al, where ITO was the transparent electrode and Al was the back electrode. The cells with DIO had 21% higher efficiency, shorter sweep-out time, higher IPCE, interpenetrating donor-acceptor morphology and higher hole mobility. A decrease in efficiency of 22% in 3% DIO vs. 62% for 0% DIO cells was observed with time. Aged cells with DIO had smaller donor/acceptor domains, higher hole mobility, lower sweep-out times and higher photocurrent generation compared to aged cells without DIO. Moreover, Raman data indicated aging affected the bonds in side chain but not the thiophene ring in P3HT. Thus DIO resulted in improved device performance and active layer morphology. The addition of DIO also enhanced stability in P3HT:PCBM bulk heterojunction solar cells.

Library of Congress Subject Headings

Solar cells -- Properties.


Includes bibliographical references (pages 87-105).



Number of Pages



South Dakota State University


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