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A study on the photoresponsive characteristics of CdSe/ZnS quantum dot and π-conjugated molecule hybrid 원문보기

  • 저자

    Han Yoon Deok

  • 학위수여기관

    고려대학교 대학원

  • 학위구분

    국내박사

  • 학과

    물리학과

  • 지도교수

    주진수

  • 발행년도

    2014

  • 총페이지

    156

  • 키워드

    quantum dot hybrid;

  • 언어

    eng

  • 원문 URL

    http://www.riss.kr/link?id=T13541922&outLink=K  

  • 초록

    Semiconducting quantum dots (QDs) have unique optical properties and are promising nanostructures for optoelectronics and photonics. The hybrid nanostructures of the n-type QDs with p-type π-conjugated molecules are new building blocks for nanoscience and nanotechnology, because of controllable electrical and optical properties due to energy and charge transfer effects. In this dissertation, the QD/π-conjugated molecule hybrids with various electrical and optical properties are studied in terms of energy and charge transfer effects. Hybrids consisting of an n-type CdSe/ZnS QD as a core and p-type π-conjugate molecules as a shell were fabricated using a ligand exchange method. The CdSe/ZnS QDs with various diameters and functionalized π-conjugated molecules have been synthesized for the hybridization. π-Conjugated macromolecular dioctyloxybenzodithiophene-based polythiophene (P3000), a single carbazole (CB) with insulating molecular blocks, or thiol-group functionalized poly(3-hexylthiophene) (P3HT) were attached to the QD surface. For the QD-P3HT hybrids, the various molecular weights (Mws) of P3HT were prepared. To study the morphology and structure of QD and π-conjugate molecule hybrids, high resolution transmission electron microscope (HR-TEM), electron energy loss spectroscopy (EELS) and Fourier transform infrared spectroscopy (FT-IR) experiments were performed. The ultra violet and visible (UV/Vis) absorption spectra and solution photoluminescence (PL) spectra were measured for optical properties. The nanoscale photoluminescence (PL) of the QD/π-conjugated-molecule hybrids were measured using the laser confocal microscope (LCM). Using the time-resolved PL (trPL) spectroscopy, the exciton dynamics were studied and transient absorption (TA) spectroscopy experiments were performed to investigate the energy/charge transfer between n-type QDs and the p-type π-conjugated molecules. The nanoscale LCM PL characteristics for the single QD were drastically changed through close contact with P3000 or functionalized P3HT owing to energy and charge transfer effects. Interestingly, with increasing the molecular weight (Mw) of P3HT, the charge transfer effect became severe. However, for the QD-CB hybrids, the LCM PL of the QD was dominant because of weak energy transfer resulting from the negligible spectral overlap and relatively longer insulating molecular block between the QD and the CB molecule. On the basis of the TA spectra, the charge transfer effect was founded for QD-P3000 and QD-P3HT hybrids not for QD-CB hybrids. From trPL spectra, the exciton lifetimes of the QD in the QD-P3000 (or QD-P3HT) hybrids and QD-CB hybrids were clearly different because of a distinct variation in the energy transfer rate. Depending on the structures of p-type π-conjugated molecules on the surface of QDs, the exciton lifetimes of the QD in the hybrids were drastically changed. To measure the photoresponsive electrical properties of QD/π-conjugated molecule hybrids, the conducting atomic force microscope (CAFM) was used. The photocurrents of the single QD-P3000 hybrid were considerably higher and actively responded to both forward and reverse biases due to the energy and charge transfer effects, while those of the single QD-CB hybrid exhibited diode characteristics. The photovoltaic characteristics of a single QD-P3HT hybrid drastically varied with the Mw of P3HT. Monochromatic power conversion efficiency of QD-P3HT hybrids increased with an increase in the Mw of P3HT, suggesting sufficient photoinduced charge transfer between the QD and highly ordered P3HT chains. The measured nanoscale optical characteristics of the QD/π-conjugate molecules hybrids support their distinct photoresponsive behaviors. In summary, the nanoscale optical and electrical properties of QD/π-conjugated molecules hybrids were controllable through the structures and Mw of π-conjugated molecules on the basis of the energy and charge transfer effect, resulting from the spectral overlap and the separation distance.


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