Search or add a thesis

Advanced Search (Beta)
Home > Preparation, Characterization and Applications of Quantum Dots in Conducting Polymer Composites and Low Cost Devices

Preparation, Characterization and Applications of Quantum Dots in Conducting Polymer Composites and Low Cost Devices

Thesis Info

Access Option

External Link

Author

Chughtai, Ambreen Ayub

Program

PhD

Institute

Quaid-I-Azam University

City

Islamabad

Province

Islamabad.

Country

Pakistan

Thesis Completing Year

2019

Thesis Completion Status

Completed

Subject

Physics

Language

English

Link

http://prr.hec.gov.pk/jspui/bitstream/123456789/12619/1/Ambreen%20ayub%20chughtai%20QAU%20isb%20physics%20year%202019.docx

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676726998170

Asian Research Index Whatsapp Chanel
Asian Research Index Whatsapp Chanel

Join our Whatsapp Channel to get regular updates.

Similar


Owing to the growing importance of quantum dots in future materials and devices, this thesis mainly concerns with the synthesis, characterization and applications of quantum dots in conducting polymer composites and devices such as Schottky diodes and quantum dot sensitized solar cells (QDSSCs). Quantum dots (QDs) involved in these studies include II-VI semiconductors cadmium selenide (CdSe) and cadmium sulfide (CdS) and IV-VI semiconductor lead sulfide (PbS). As regards the work related to application of QDs in functional materials, CdSeQDs have been synthesized, characterized and incorporated in polyaniline (PANI). CdSe/PANI nanocomposites have been prepared with varying amounts of CdSe QDs in PANI by in-situ polymerization technique. Pure PANI, CdSeQDs and their composites have been characterized by using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and UV-VIS absorption spectroscopy. The surface morphologies have been investigated by Scanning Electron Microscopy (SEM). The electrical and dielectric properties have been studied by using 4-probe mechanism and LCR meter respectively. The DC conductivity of the nanocomposites has been studied in the temperature range from 298 to 368 K and it is increased with the temperature risedepicting the semiconducting behavior of the samples. DC conductivity is found to follow Mott’s 1D (one dimension) variable range hopping model. It is observed that AC conductivity of the samples is enhanced with the increase in temperature and the frequency dependent AC conductivity follows the universal power law. Dielectric behavior of the nanocomposites discussed as a function of frequency and temperature exhibits a rapid fall of dielectric constant with rise in frequencywhich can be described by Maxwell-Wagner capacitor model. It is observed that the dielectric constant is increased with the increasing temperature and also with the increase of QDconcentration in the nanocomposites. Two Schottky devices have also been fabricatedto study the device application ofCdSe/PANI nanocomposites. One device was fabricated employing layer-by-layer deposition of PANI and CdSe films on PEDOT-PSS/ITOcoated glass substrate {ITO (indium tin oxide)/PEDOT-PSS [poly (ethylene dioxy thiophene) poly (styrene sulphonate)]/PANI (polyaniline)/CdSe (cadmium selenide)} and the other by depositing PANI-CdSeQDs composite film on the same substrate (ITO/PEDOT-PSS/CdSe-PANI) using spin coating technique. The diode performance parameters have been compared and J-V characteristics of these devices show a rectifying contact with aluminum metal, however, with variation in performance parameters like barrier height, ideality factor and reverse saturation current density, the ITO/PEDOT-PSS/CdSe-PANI/Al (composite assembly) device exhibits better diode performance as compared to ITO/PEDOT-PSS/PANI/CdSe/Al (layer-by-layer) device.This work has been presented in Chapter 5 of this thesis. Fabrication and study of two series of low cost QDSSC devices prepared by varying successive ionic layer adsorption and reaction (SILAR) cycles: ITO/TiO2/CdS/CdSe/ZnS QDSSCs and FTO/TiO2/PbS/CdS/CdSe/ZnS QDSSCsare reported in Chapter 6 of this thesis.The structural, optical, morphological and electrical properties of these devices have been studied. Different modes of vibrations in the deposited films have been studied by RAMAN spectroscopy. X-ray Diffraction (XRD) patterns show that the particle size of the QDs increases with the number of SILAR cycles. However, the intensity peak of CdS QDs has not been observed after three SILAR cycles. UV-VIS spectroscopy measurement of the devices show enhancement in absorbance upto three SILAR cycles and saturation for further SILAR cycles. The SEM images of devices reveal capping of CdS QDs by CdSe QDs for four and higher SILAR cycles, resulting decrease in power conversion efficiency (PCE) of these devices. The J-V characteristics show that in order to achieve the best performance of QDSSC, the optimum parameters for CdS and CdSe QDs deposition are three cycles. The highest PCE of 5.0 % has been achieved after an optimization of dipping SILAR cycles. After adding 3 SILAR cycles of PbS QDs, the PCE value has been improved upto 6.43 %. Electrochemical Impedance Spectroscopy has been performed under dark conditions in order to discuss the physical mechanism of QDSSCs. Maximum values of recombination resistance (Rrec) and constant phase element (CPE) have been found for efficient devices with three SILAR cycles: ITO/TiO2/3CdS/3CdSe/3ZnS and FTO/TiO2/3PbS/3CdS/3CdSe/3ZnS QDSSCs. Lower and higher numbers of SILAR cyclesgive lower values of Rrec and CPE in all other QDSSCs. This shows that the charge carriers in QDSSCs with three SILAR cycles can be efficiently transported because of longer carrier lifetimes in these devices.
Loading...
Loading...

Similar Books

Loading...

Similar Chapters

Loading...

Similar News

Loading...

Similar Articles

Loading...

Similar Article Headings

Loading...

پنڈت جواہر لال نہرو

آہ جواہر لال
ہندوستان کی عظمت کا آفتاب غروب ہوگیا
جس نازک وقت کا خطرہ کروڑوں دلوں کو مضطرب کیے رہتا تھا بالآخر پیش آکر رہا اور جو آواز تقریباً نصف صدی تک ہندوستان کے در و دیوار میں گونجتی رہی ہمیشہ کے لیے خاموش ہوگئی وہ حیات آفریں جس نے ہندوستان کی مردہ رگوں میں زندگی کی روح پھونکی، خود موت کے آغوش میں سوگیا۔ وہ آفتاب جس کی ضیاباریوں نے نہ صرف ہندوستان کو منور کیا بلکہ دوسرے ملکوں تک اس کی روشنی پھیلی، ۲۷؍ مئی کو عین دوپہر کے وقت ہمیشہ کے لیے غروب ہوگیا۔ پنڈت جواہر لال کی موت ایسا حادثہ نہیں جس کو زمانہ کی گردش بھلاسکے، ان کا جسم گوخاک میں مل چکا ہے لیکن ان کی روح ہندوستان میں ہمیشہ زندہ رہے گی اور اس کے ذر ے ذرے پر ان کا نام ثبت رہے گا۔
وہ آزاد ہندوستان ہی کے بانی اور اس کے معمار نہ تھے، بلکہ پورے ایشیا کی آبرو اور دنیا کی عظیم شخصیتوں میں تھے، ہندوستان نے اب تک جتنی بڑی شخصیتیں پیدا کیں ان میں بعض قدیم مذہبی پیشواؤں کو چھوڑ کر پنڈت جواہر لال کا درجہ سب میں بلند تھا، انھوں نے نصف صدی تک ہندوستان کی مسلسل اور ان تھک خدمت کی، وہ جنگ آزادی کے سپہ سالار بھی تھے، آزاد ہندوستان کے معمار بھی اور اس کے محبوب لیڈر بھی، اس لیے انھوں نے دلوں پر حکمرانی کی اور کل سترہ سال میں جو قوموں اور ملکوں کی عمر کے لحاظ سے نہایت قلیل مدت ہے، ہندوستان کا درجہ ساری دنیا میں بلند کردیا۔
پنڈت جواہر لال کی جیسی تاریخ ساز شخصیتیں صدیوں میں پیدا ہوتی ہیں اور اپنا نام صفحہ عالم پر ہمیشہ کے لیے ثبت کرجاتی ہیں، ان میں جتنے اوصاف جمع تھے مشکل ہی سے کسی ایک انسان...

Historical, Cultural and Geographical Ties Between Pakistan and Iran

In order to get a vivid picture of Pakistan-Iran relations, the paper delves into the past with Iranian history and Iranian sphere of influence in South Asia. Both South Asia and Iran have ancient historical, cultural and religious ties since the times of the Cyrus the Great to the present. The Persian language and literature particularly the Persian classical poetry have left a great impression on sub-continent’s cultural and educational canvass. Pakistan-Iran border which was drawn by the British in the 1880s, remains still intact. Though the border is a wasteland with little agriculture but on the sea-front both the countries have access to the Strait of Hormuz which is of great strategic importance. Moreover, ethnic Baloch live on both sides of the border and crossborder and trade and livestock is the mainstay of cross-border economy. During the Cold War period, both Pakistan and Iran were subservient to the US policies against the Soviet Union; consequently, both received massive arms and equipment. This paper also indicates that during Mohammed Reza Shah’s time, the relations between Pakistan and Iran were quite friendly but they underwent a change after the Iranian revolution and during General Zia’s time. The main issues have been spelled out up-till 1979 and the minor frictions between the two countries could be managed through diplomacy. External pressures are also influencing the contemporary relations between the two countries and have put Pakistan in a dilemma. Historical and secondary sources have been used for the conduct of the study. Historical research has an important role to play in the Social Sciences. It helps us to understand the present by highlighting the past events.

Aromatic/ Heterocyclic Sulfonamides Containing Chromone Moieties and Their Transition Metal Complexes: Synthesis, Structural Elucidation and Evaluation of Biological Activities

Carbonic anhydrases (CA E.C. 4.2.1.1) are zinc containing metalloenzymes found in both prokaryotes and eukaryotes where they perform important physiological functions. CA has at least 16 different isozymes many of which are important drug targets. Sulfonamides and its metal derivatives are well established inhibitors of CA. The task of developing a new class of chromone containing sulfonamide CA inhibitors was taken up in this research/thesis. Consequently cobalt (II), nickel (II) and copper (II) transition metal complexes were also synthesized and tested as inhibitors of CA. An assortment of structurally diverse aromatic/heterocyclic sulfonamides containing chromone moieties were synthesized by condensation of various substituted and un-substituted 4-oxo-4H-1-benzopyran-3-carboxaldehydes with different aminobenzenesulfonamides. Compounds L1, L4, L7 and L10 were prepared by reacting 4-oxo-4H-1-benzopyran-3-carboxaldehyde (C10H6O3) and substituted 4- oxo-4H-1-benzopyran-3-carboxaldehydes (R1R2-C10H4O3, R1 = F, Br; R2 = H, Br) with 4-aminobenzenesulfonamide (4-ABS). Compounds L2, L5, L8 and L11 were prepared by reacting above chromone-3-carboxaldehydes with 3- aminobenzenesulfonamide (3-ABS). Similarly compounds L3, L6, L9 and L12 were obtained by reaction with 2-aminobenzenesulfonamide (2-ABS). Compounds L13- L17 were prepared by reaction of 4-oxo-4H-1-benzopyran-3-carboxaldehyde and 4- oxo-6-fluoro -4H-1-benzopyran-3-carboxaldehydes with N-(heteroaryl)substituted sulfonamides. In case of reactions with 3-ABS and 4-ABS, enamine products of type and 4-[{(2-ethoxy-6-(un)substituted-4-oxo-chroman)3-ylidene}methylamino] xv benzenesulfonamides were obtained. However, on reaction with 2-ABS, a benzothiadiazine product containing chromone moiety at 3-position resulted due to cyclization. Only 4-oxo-6,8-dibromo-4H-1-benzopyran-3-carboxaldehyde proved to be the only exception giving an enamine product, 2-[{(2-ethoxy-6,8-dibromo-4-oxo- chroman)3-ylidene}methylamino]benzenesulfonamide. Stable, non electrolyte, non polymeric metal complexes were obtained in good yields by reacting Co (II), Ni (II) and Cu (II) acetates with above compounds under basic conditions. Molecular structure of all fifty three compounds (both ligands and their complexes) was ascertained by means of IR, 1H-NMR, 13C-NMR, MS and elemental (C, H, N) analysis. The metal content of the metal complexes was determined by AAS. In case where suitable crystals were available, single crystal X-ray diffraction was carried out. In view of CA inhibitory role of sulfonamides and their metal complexes, CA inhibitions activity of all the compounds and their metal complexes was evaluated against bovine cytosolic enzyme containing CA-I and CA-II. All compounds containing free sulfonamide group showed excellent CAI activity (IC50values are in the range 4.31 to 29.12 μmoles). Compounds containing substituted sulfonamide group were found to be inactive as CAIs. Among metal complexes copper complexes were most active followed by some nickel complexes; cobalt complexes were not very active as CAIs. DPPH radical scavenging activity for all the compounds was also evaluated. Only compounds L12 and L14 showed moderate activity (67 and 41 % inhibition respectively). None of the other compounds showed outstanding radical scavenging activity.