Optoelectronic Properties Of Copper Indium Sulfide Based Semiconductor Quantum Dots And Their Application

The semiconductor quantum dots (QDs) have more attention with the uniqueoptical properties because the quantum confinement. These properties made the QDsattractive for biological, optoelectronic and photovoltaic applications. Based on theopinion of green chemistry, this dissertation investigated the low toxic I-III-VI QDsincluding the synthesis, optical mechanism and applications. The main results arelisted as follows:1. The reaserch of the optical mechanism has been suggested. We synthesize theCuInS2QDs, CuInS2/ZnS core/shell QDs, and ZnCuInS/ZnSe/ZnS core/shell/shellQDs. The optical properties have been observed such as the wide spectra and largeStokes shift. Those were determined by the structure of gap band and opticalmechanism. The large Stokes shift proved that the transition was related to the defectlevels. The optical band gap shift with different size obviously were observed whichwas because of the quantum confinement effect. This proved that the dominatingrecombination was not DAP recombination. The temperature-dependentphotoluminescence (PL) and time-resolved PL spectra of ZnCuInS/ZnSe/ZnS QDs,CuInS2and CuInS2/ZnS QDs with different Cu/In ratio (CuxIn1-xS) have beenmeasured. According to the analysized the spectra above, the recombination of thoseQDs have been investigated deeply. There were several progress of recombination,they were surface-related recombination, conduction band-defect levelrecombination, and DAP recombination. And then, we changed the Cu/In ratio ofCuxIn1-xS and CuxIn1-xS/ZnS QDs. The mechanism of recombination with differentCu/In ratio has been investigated through the temperature-dependent PL spectra. Theresult indicated that the proportion of DAP recombination was boosted by theincrease of In composition.2. The application of a micrometer resolution and plane-array temperature sensing using the PL of ZnCuInS/ZnSe/ZnS QDs. The QDs were directly depositedon a printed circuit board (PCB) to analyze the surface temperature of the devices onit. An optical fiber monochromator and a high-power microscope were employed tofabricate a system which could collect the temperature-dependent QD emission fromthe micrometer area for the temperature measurements. This system realizes theimaging of the surface temperature distribution in the planar micrometer area. Thetemperature sensitivity of the PL intensity reached0.66%/oC-1, and the relative errorwas lower than1.9%.3. The quantum dot light-emitting diodes (QD-LEDs) were fabricated by red-,yellow-, and green-emitting ZnCuInS/ZnSe/ZnS QDs and blue GaN chips. Thepower efficiencies were measured as14.0lm/W for red,47.1lm/W for yellow, and62.4lm/W for green LEDs at2.6V. The temperature effect of ZnCuInS/ZnSe/ZnSQDs on these LEDs was investigated using CIE chromaticity coordinates, spectralwavelength, full width at half-maximum (FWHM) and power efficiencies (PE). Thethermal quenching induced by the increased surface temperature of the device wasconfirmed to be one of the important factors to decrease power efficiencies while theCIE chromaticity coordinates changed little due to the low emission temperaturecoefficients of0.022,0.050and0.068nm/°C for red-, yellow-and green-emittingZnCuInS/ZnSe/ZnS QDs. This indicates that ZnCuInS/ZnSe/ZnS QDs are moresuitable for down-conversion LEDs compared to CdSe QDs.