아주대학교

초록/요약

The main contents of the paper are the fabrication of new structured quantum dots (QDs) and their specific application including light-emitting-diodes (LEDs) and photovoltaic cell. Novel synthetic routes to cadmium free, new type I-III-VI and various QDs are presented. The development of new structure core/shell/shell QDs (ZnSe/InP/ZnS, InP/GaP/ZnS) is discussed in the context of structure analysis of QDs and making highly luminous efficiency and stable White-LEDs. In Chapter 1, Highly luminescent cadmium-free QDs with a reverse type-I core/shell/shell structure consisting of ZnSe/InP/ZnS were developed. Their emission color could be tuned from violet to red by controlling the InP shell thickness. The final layer of ZnS improved the quantum yield. (QY) In Chapter 2, Highly stable and luminescent InP/GaP/ZnS QDs with a maximum quantum yield of 85% were synthesized by in situ method. The GaP shell rendered passivation of the surface and removed the traps. Time Correlated Single Photon Counting (TCSPC) data showed an evidence for the GaP shell. InP/GaP/ZnS QDs show better stability than InP/ZnS. We studied the optical properties of white QD-LEDs corresponding to various QD concentrations. Among various concentrations, the white QD-LEDs with 0.5 mL of QDs exhibited a luminous efficiency of 54.71 lm/W, Ra of 80.56, and CCT of 7864 K. We present new method for new type I-III-VI or gradient alloy QDs such as CuInTe2, CuInTe2-xSex. In addition, a simple method for fabricating size-tunable and stable HgTe, PbS, and PbSSe QDs in the NIR region in order to application for solar cells. The synthesis and characterization of CuInTe2, CuInTe2-xSex, PbS, PbSSe, and HgTe QDs is discussed. In Chapter 3, we report the first synthesis of colloidal CuInTe2, CuInTe2–xSex gradient alloyed QDs through a simple hot injection method. We confirmed the composition of synthesized QDs to cationic rich phase of CuIn1.5Te2.5 and Cu0.23In0.36Te0.19Se0.22 with X-ray Photoelectron Spectroscopy (XPS) and Inductively Coupled Plasma (ICP) analysis, and we have also found that the gradient alloyed Cu0.23In0.36Te0.19Se0.22 QDs exhibit greatly improved stability over the CuIn1.5Te2.5 QDs. The solution-processed solar cell based on the gradient alloyed Cu0.23In0.36Te0.19Se0.22 QDs exhibited 17.4 mA/cm2 of short circuit current density (Jsc), 0.40 V of open circuit voltage (Voc), 44.1% of fill factor (FF), and 3.1% of overall power conversion efficiency at 100 mW/cm2 AM 1.5G illumination. In Chapter 4, Bandgap-engineered monodisperse HgTe NCs of different sizes were synthesized by means of a facile temperature-control method, a non-aqueous and non-Te-gas process. The photo-physical properties of the synthesized NCs in a simple photovoltaic device were tested. It was shown that this cell is capable of processing signals up to the 100 kHz level below 3 dB and hence is suitable for use in NIR photodetection and We have demonstated the successful fabrication of multiplelayer colloidal quantum dot (CQD)-sensitized near-infrared (NIR) photovoltiac (PV) cells using the solution processible HgTe CQDs and poly-3(hexylthiophene) (P3HT) as hole10 conducting polymer. The cells showed the 3.6 fold enhancement in power conversion efficiency under NIR light illumination by the post-ethandithiol chemical treatment. In Chapter 5, PbS colloidal quantum dot (CQD)-sensitized inorganic–organic heterojunction solar cells fabricated by using the PbS CQDs co-capped by the oleic acid (OA) and 1-dodecanethiol (DT) ligand showed better device stability with aging time under ambient conditions without encapsulation. Furthermore, the device performance is better than the cell fabricated from PbS CQDs without DT ligand. The enhancement of performance in OA and DT co-capped systems is investigated by impedance spectroscopy. An upward displacement of the TiO2 conduction band, with a consequent increase of Voc, results in the improved performance when CQD with DT are employed. In Chapter 6, we present an incorporation technique for inorganic nanocrystals (NCs) in organic solar cells (OSCs) for the improvement of power conversion efficiency (PCE). Ternary PbSSe NCs constitute stable conformations with regular poly(3-hexylthiophene):phenyl-C70 butyric acid methyl ester (P3HT:PCBM) organic composites under two hetero-junction systems, and significant solar performance modification was obtained.