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Effect of Polymer Molecular Weight, Binary Processing Additives, Two-Dimentional Polymer on Efficiency of Polymer Solar Cells

Liu, Chang
http://rave.ohiolink.edu/etdc/view?acc_num=akron1396895752

Abstract Details

2014, Master of Science in Polymer Engineering, University of Akron, Polymer Engineering.
In recent years, bulk heterojunction (BHJ) polymer solar cells (PSCs) have received great attention from both academic and industrial sectors as they are flexible and have large scale production potential and low-cost grid power generation. However, PSCs are still inferior to their inorganic counterparts in efficiency and stability. In order to advance large-scale commercialization and implementation, the power conversion efficiency (PCE) and stability of PSCs must be improved. There are four chapters in this thesis. In Chapter 1, the development of PSCs with an inverted device structure was overviewed. In Chapter 2, we study the effect of polymer molecular weight on the efficiency of PSCs. It was found that the PSCs performances are largely dependent on the molecular weight of PTB7 (poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]). PCE significantly enhanced from 5.41% to 6.27% and 8.50% along with the MW of PTB7 increased from 18 kg/mol to 40 kg/mol and 128 kg/mol, respectively. This enhancement is attributed to the enhanced light absorption and increased charge carrier mobility of PTB7 with high MW, and a proper phase separation in BHJ composite of PTB7:PC71BM ([6,6]-phenyl-C71 butyric acid methyl ester) interpenetrating network. Then, by using binary solvent additives to tune the phase separation domains between PTB7 and PC71BM, we successfully boosted PCE from 5.60% (pristine device) to 8.55% (BHJ composites with binary additives). In Chapter 3, we report the influence of binary additives: 1,8-octanedithiol (ODT) and 1-chloronaphthalene (CN) on the performance of PSCs. It was found that performance of PSCs based on PTB7:PC71BM as the active layer can be largely improved with incorporation of binary additives ODT and CN. PCE increased from 5.60% to 8.55%, which originates from ameliorated thin film morphology of active layer. With binary additives, crystallinity of PTB7 is demonstrated to be elevated, which in turn facilitates charge transport within the BHJ layer. Moreover, the phase separation is testified to form a more homogenous film. Through the optimization of film morphology, recombination loss mechanisms in PSCs were proved to be drastically lowered, with the elimination of geminate recombination and decreasing the nongeminate recombination to the lowest level. In Chapter 4, we report single-junction PSCs with high short circuit current density (JSC) large open circuit voltage (VOC) and high fill factor (FF) by combining complementary materials design, synthesis, and device engineering strategies. A two-dimensional donor-acceptor conjugated copolymer, poly[[2,6’-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene][3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7-DT) was developed and utilized in BHJ PSCs. Introduction of 5-alkylthiophene-2-yl unit as a conjugated side chain lowers the bandgap and facilities the p-p stacking, and improves the charge carrier mobility of PTB7-DT. These results are consistent with the observation from first-principle calculations. Consequently, the resulting polymer exhibits considerably better photovoltaic performance with PCE of 10.12 % from single-junction PSCs.
Xiong Gong, Dr. (Advisor)
Alamgir Karim, Dr. (Committee Member)
Yu Zhu, Dr. (Committee Member)
145 p.
Polymers

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Citations

  • Liu, C. (2014). Effect of Polymer Molecular Weight, Binary Processing Additives, Two-Dimentional Polymer on Efficiency of Polymer Solar Cells [Master's thesis, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1396895752

    APA Style (7th edition)

  • Liu, Chang. Effect of Polymer Molecular Weight, Binary Processing Additives, Two-Dimentional Polymer on Efficiency of Polymer Solar Cells. 2014. University of Akron, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1396895752.

    MLA Style (8th edition)

  • Liu, Chang. "Effect of Polymer Molecular Weight, Binary Processing Additives, Two-Dimentional Polymer on Efficiency of Polymer Solar Cells." Master's thesis, University of Akron, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1396895752

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.