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Home > Fabrication and Study of Photovoltaic Devices Using Macrocyclic Organic Semiconductors

Fabrication and Study of Photovoltaic Devices Using Macrocyclic Organic Semiconductors

Thesis Info

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Author

Khan, Shahid Mahmood

Program

PhD

Institute

Ghulam Ishaq Khan Institute of Engineering Sciences and Technology

City

Topi

Province

KPK

Country

Pakistan

Thesis Completing Year

2012

Thesis Completion Status

Completed

Subject

Applied Sciences

Language

English

Link

http://prr.hec.gov.pk/jspui/handle/123456789/505

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676726189209

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During the last decade, different structures of photovoltaic (PV) cells fabricated from organic semiconductors have drawn tremendous economic and scientific interest due to their high optical absorption efficiency, low fabrication cost, lightweight, high mechanical flexibility and continuous growth of their power conversion efficiencies. Bulk heterojunction organic solar cells can be fabricated by simple processing techniques, such as, screen printing, spin casting, etc., and, therefore, are potential candidates for the mass production of flexible and cost-effective devices. In this dissertation, based on the soluble macrocyclic organic semiconductors 5,10,15,20- tetraphenyl-21H,23H-porphine zinc (ZnTPP) and copper (II) tetrakis (4-cumylphenoxy) phthalocyanine (Tc-CuPc) bulk heterjunction structures of ITO/PEDOT:PSS/ZnTPP:PCBM/Al and ITO/PEDOT:PSS/Tc-CuPc:PCBM/Al were fabricated employing spin casting and vacuum thermal evaporation techniques. The effect of donor to acceptor (D:A) mass ratio was investigated on photovoltaic properties of the ZnTPP:PCBM BHJ solar cell and the optimum D:A ratio was identified. Effect of the thickness and surface morphology of the active layer on the photovoltaic properties of this porphyrin-fullerne BHJ was also studied and the optimum active layer thickness was identified. Bulk and hybrid-bilayer heterojunctions of copper (II) tetrakis (4- cumylphenoxy) phthalocyanine (Tc-CuPc) and vanadyl 2,9,16,23-tetraphenoxy- 29H,31H-phthalocyanine (VOPcPhO) heterojunctions were also fabricated. Temperature dependent electrical properties of these devices and optical performance of the Tc- CuPc:PCBM bulk heterojunction was also investigated. Macrocyclic semiconductors e.g. metallo-phthalocyanines (MPcs) and metallo- porphyrins (MPPs), are restricted to dry processing techniques due to their insolubility in common organic solvents. Thus MPcs and MPPs are used in typical thermally evaporated donor-acceptor bi-layered solar cells. The performance of bi-layer solar cells is low due to small exciton diffusion length; only the excitons generated within 10 nm from the D/A interface are expected to contribute to photocurrent. This issue is resolved in BHJ architecture, in which the D-A interfacial area is distributed throughout the volume (bulk) viiiof the active layer. In other words the D-A interface is brought near to the exciton generation site. Soluble versions of MPcs and MPPs can be helpful to study their opto- electronic characteristics in BHJ solar cell architecture. In BHJ architecture there is a lot of flexibility and ease for rapid research e.g. changing solvent, varying concentration, using different D to A mass ratios, changing active layer thicknesses by spin coating at different speeds, incorporating different exciton-blocking layers etc. A lot of variations can be studied in a very short time and with less cost. However, as more and more research groups start studying soluble macrocyclic organic semiconductors in BHJ solar cells, further efficiency improvements and availability of new soluble macrocyclic materials are worthwhile. Since the microstructure of bulk heterojunction layer is strongly dependent on the donor to acceptor (D:A) mass ratio, an optimum D:A ratio improves device performance by improving the charge separation, transport and collection process. As one aspect of this research work, porphyrin-fullerne BHJ solar cells with ITO/PEDOT:PSS/ZnTPP:PCBM/Al structure were fabricated with different D:A mass ratios and their optical parameters were measured both under simulated solar spectrum AM 1.5G and monochromatic illuminations. The active layer thicknesses were extracted from their respective optical reflection and transmission measurements using average absorption coefficient. Scanning electron microscope (SEM) image of the device cross section was studied to verify layer thicknesses and examine the quality of layers. Effect of thermal annealing on performance of some devices was also studied. Incident photon- to-current conversion efficiency (IPCE) spectra at different D:A ratios was determined. On basis of the measured optical parameters such as fill factor FF, open circuit voltage V OC , short circuit current density J SC , and power conversion efficiency η , the optimum D:A ratio was identified. Maximum IPCE value of 21% was obtained for D:A ratio of 1:9 which lead to PCE of 0.21% which was 36 times better than a previously reported value in which C 60 was used as acceptor. Also incorporating PCBM as the acceptor instead of C 60 improved the open circuit voltage (V OC ) for all the D:A ratios. The reason for high V OC is greater difference between the ZnTPP HOMO and PCBM LUMO . Furthermore the 1:9 devices showed consistency in optical parameters when reproduced.
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Preparation, Quality Control and Bio-Evaluation of Technetium-99M Labeled Compounds for Infection and Tumor Imaging

The aim of the proposed research work was to label some drugs/compounds with medically interesting Tc-99m. For this purpose antibiotics clarithromycin, clindamycin, vibramycin and peptide cecropin A were labeled with Tc-99m as infection imaging agents using animal models whereas epirubicin, vincristine and lanreotide peptide were chosen for tumor study. In the present investigation, synthesis of the 99mTc-clarithromycin and its biological evaluation in mice artificially infected with Staphylococcus aureus was evaluated. A good labeling efficiency (More than 99%) with 99mTcO4 - was achieved at pH 6–7 while 25 μg using stannous chloride as reducing agent and 500 μg of clarithromycin at room temperature. Electrophoresis indicates the neutral behavior of 99mTc-clarithromycin. HPLC analysis confirms the single specie of the labeled compound. Biodistribution and SPECT imaging of 99mTc-clarithromycin was performed in infection induced Swiss Albino mice and rabbits respectively which revealed high uptake of 99mTc-clarithromycin at Staphylococcus aureus infected sites in model animals. Clindamycin, a lincosamide antibiotic was labelled with technetium-99m (~380 MBq). Clindamycin has proved to be efficient for treating serious infections caused by bacteria such as staphylococcus aureus. More than 95% labeling efficiency with 99mTc was achieved at pH 6–7 while using 2.5–3 μg SnCl2.H2O as reducing agent and 100 μg of ligand at room temperature. The characterization of the compound was performed by using electrophoresis, HPLC and shake flask assay. Electrophoresis indicates the neutral behavior of 99mTc-clindamycin. HPLC analysis confirms the single specie of the labeled compound, while shake flask assay confirms high lipophilicity. The biodistribution studies of 99mTc-clindamycin were performed Sprague-Dawley rats bearing bacterial infection. Scintigraphy and biodistribution studies showed high uptake of iii 99mTc-clindamycin in the liver, heart, lung, and stomach as well as at S. aureus infected sites in rabbits. A new technetium-99m labeled vibramycin radiopharmaceutical, labeled with technetium-99m using SnCl2.2H2O as a reducing agent is also prepared. The stability of 99mTc-vibramycin was evaluated in human serum at 37 0C. Biodistribution studies of 99mTc-vibramycin were performed in a model of bacterial infected Sprague-Dawley rats. In vitro studies were performed to determine the binding interaction of the labeled antibiotic with bacteria and its stability. Scintigraphic study was done with a γ-camera at 1, 4 and 24 hours after radiotracer injection in rats having infectious intramuscular lesions. 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In vivo study of peptides/receptor systems with medical radiotracers have great potential across the whole range of nuclear medicine investigations, their initial focus was in oncology and the present interest has focused especially on the field of inflammation and infection. 99mTc-labeled antimicrobial peptide cecropin A was evaluated as a bacterial infection seeking agent in iv Escherichia coli induced infections. 99mTc-cecropin A was tested for stability at room temperature, stability in human serum, cysteine challenge test and bacterial binding study. Experimental thigh muscle infection was induced by injecting 2×108 cfu of live E. coli bacteria into the right thigh muscle in mice and rabbits. Heat-killed E. coli and turpentine oil were used for inducing sterile thigh muscle inflammation. In Scintigraphic imaging, regions of interest were drawn over infected (T) and non-infected (NT) thigh, and accumulation of 99mTc-cecropin A at sites of infection was expressed as a target to non-target ratio. Direct radiolabeling of epirubicin with 99mTc, quality control, biological characterization and scientigraphic evaluation in tumor bearing mice was done. The optimum conditions ensuring 99mTc-epirubicin labeling yield as high as 99% by adding 35μg SnCl2.2H2O, 200μg of ligand at pH 6 for 30 minutes reaction time at room temperature (25°C±2°C). The radiochemical purity of 99mTc-epirubicin was evaluated by chromatographic techniques. HPLC of 99mTc-epirubicin shows about 99% binding of the compound with technetium-99m. Electrophoresis study indicates the neutral nature of 99mTc-epirubicin. Biodistribution data and scintigraphic results showed that 99mTc-epirubicin accumulated in the tumor with significant uptake and excellent retention. 99mTc-epirubicin shows good stability in human serum. In vitro and in vivo studies showed significantly selective uptake of 99mTc-epirubicin in the tumor, indicating efficiency of 99mTc-epirubicin as a tumor diagnostic agent. Methodology was developed for the preparation of DOTA-lanreotide and labeling with 99mTc. The radiochemical purity of 99mTc-DOTA-lanreotide was evaluated by chromatographic techniques. Labeling efficiency of 96% was obtained using 5 μg of ligand (DOTA-lanreotide), with 4 μg SnCl2.2H2O as a reducing agent at pH 7 at room temperature for 30 minutes. The v stability of 99mTc-DOTA-lanreotide was studied up to 4 h. Electrophoresis indicated that 99mTc- DOTA-lanreotide has no charge and HPLC shows a single species of labeled compound. Biodistribution studies of 99mTc-DOTA-lanreotide were performed in normal and tumor induced Swiss Webster mice at various time intervals after intravenous administration. The biodistribution and scintigraphic results in tumor bearing mice show accumulation of 99mTc- DOTA-lanreotide in tumor sites. These results suggest that 99mTc-DOTA-lanreotide may be useful as a selective imaging agent for diagnosis and visualization of tumors. The study was also performed for the radiolabeling and biological testing of vincristine labeled with 99mTc. The optimum conditions required to obtain ~100% yield of 99mTc-vincristine(99mTcvinc) were as follows: pH 4, 5 μg of vincristine sulphate , 6 μg SnCl2.2H2O as reducing agent and 10 min incubation time at room temperature. The labeling yield was confirmed by HPLC using radioactive and UV detector operating at 230 nm. 99mTc-vinc was stable in vitro for 5 h. Biodistribution and scintigraphy of 99mTc-vinc was performed in normal mice (Swiss Albino mice) and rabbits respectively and that showed high uptake of it in liver and spleen. Biodistribution of 99mTc-vinc in solid tumor bearing mice showed accumulation of major activity in tumors. Therefore 99mTc-vinc can be important radiopharmaceutical in the detection and follow up of tumor in patients simultaneously with chemotherapy.