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Performance and Active Layer Morphology of P3HT-PCPDTBT Organic Photovoltaic Cells

Mulderig, Andrew J

Abstract Details

2016, MS, University of Cincinnati, Engineering and Applied Science: Materials Science.
The Sun has long been the most important energy source for planet Earth. Sunlight offers the potential to function as a source of clean, renewable energy; photovoltaic (PV) cells have been designed to tap into this abundant solar energy to generate electricity. Organic photovoltaic (OPV) devices show promise as technologies capable of lightweight, low cost and flexible alternatives to traditional silicon PV but the nature of conjugated organic and polymeric semiconductors have limited performance and, therefore, application. However, recent advances have shown that the addition of pristine graphene (PG) to the active layer of OPV devices can yield three-fold performance improvements in blends of P3HT (poly(3-hexylthiophene-2,5-diyl) & PCBM (phenyl C61 butyric acid methyl ester) and, later, in all-polymer blends of P3HT & F8BT (poly(9,9-dioctylfluorene-alt-benzothiadiazole).1,2 In both OPV systems, increased performance is believed to be due to high charge carrier mobility imparted by the PG additive to the composite active layer blend. In this work, the effect of addition of PG to the active layer blend of P3HT & PCPDTBT (poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]) systems was investigated. PV devices were designed, fabricated and tested using standard processing methods and testing procedures. Although PG increased OPV device performance relative to samples without PG, power conversion efficiency (?) on an absolute scale was lower than expected despite the otherwise complementary properties of these materials. Based on the literature, the low performance of these devices was hypothesized to result from non-ideal active layer morphology, lacking charge carried percolation pathways to the electrodes. Small angle neutron scattering (SANS) was employed to probe the active layer morphology in polymer blend films similar to the active layers of the cells. Deuterated P3HT (d-P3HT) was used to exploit the large scattering length density (SLD) contrast between hydrogen and deuterium. Rigorous analysis of the SANS data allowed the nanostructure to be determined and a model of disk-like d-P3HT crystallites dispersed in a matrix of the amorphous polymers was constructed. This structure shows limited interfacial area for exciton dissociation and exhibits a lack of charge percolation pathways to the electrodes. Morphological insight offered by SANS analysis along with literature review allowed higher performance all-polymer photovoltaic cells to be designed and tested using the same semiconducting polymers. By introducing a co-solvent and modifying the thermal annealing procedure, significant performance gains were realized for subsequent devices. The increased performance observed following the change in procedure is believed to be due to enhanced active layer morphology and formation of a bulk heterojunction (BHJ) structure, to be studied in future work. Although there is room for further performance gains in P3HT-PCPDTBT devices as well as application to other OPV systems in future work, the methods, results and discussion presented here highlight the importance of structure-property relationships in all-polymer photovoltaic cells.
Gregory Beaucage, Ph.D. (Committee Chair)
Jude Iroh, Ph.D. (Committee Member)
Vikram Kuppa, Ph.D. (Committee Member)
Dale Schaefer, Ph.D. (Committee Member)
84 p.

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Citations

  • Mulderig, A. J. (2016). Performance and Active Layer Morphology of P3HT-PCPDTBT Organic Photovoltaic Cells [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1457619609

    APA Style (7th edition)

  • Mulderig, Andrew. Performance and Active Layer Morphology of P3HT-PCPDTBT Organic Photovoltaic Cells. 2016. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1457619609.

    MLA Style (8th edition)

  • Mulderig, Andrew. "Performance and Active Layer Morphology of P3HT-PCPDTBT Organic Photovoltaic Cells." Master's thesis, University of Cincinnati, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1457619609

    Chicago Manual of Style (17th edition)