Novel light-sensitive nanocrystal skins

buir.advisorDemir, Hilmi Volkan
dc.contributor.authorAkhavan, Shahab
dc.departmentGraduate Program in Materials Science and Nanotechnologyen_US
dc.descriptionAnkara : Materials Science and Nanotechnology and the Graduate School of Engineering and Science of Bilkent Univ., 2013.en_US
dc.descriptionThesis (Master's) -- Bilkent University, 2013.en_US
dc.descriptionIncludes bibliographical references leaves 89-100.en_US
dc.description.abstractLight sensing devices traditionally made from crystalline or amorphous silicon, operating at the visible and near-infrared wavelengths, have led to a multibillion-dollar annual market. However, silicon faces various limitations including weak detection at long wavelengths (insufficient beyond 1.1 µm) with a cut-off at short wavelengths (in the ultraviolet) and small-area applications. On the other hand, solution-processed semiconductor nanocrystals (NCs), also known as colloidal quantum dots, offer large-area light sensing platforms with strong absorption cross-section. In this thesis we propose and demonstrate a new class of large-area, semi-transparent, light-sensitive nanocrystal skin (LS-NS) devices intended for large-surface applications including smart transparent windows and light-sensitive glass facades of smart buildings. These LS-NS platforms, which are fabricated over areas up to many tens of cm2 using spraycoating and several cm-squares using dip-coating, are operated on the basis of photogenerated potential buildup, as opposed to conventional charge collection. The close interaction of the monolayer NCs of the LS-NS with the top interfacing metal contact results in highly sensitive photodetection in the absence of external bias, while the bottom side is isolated using a high dielectric spacing layer. In operation, electron-hole pairs created in the NCs of the LS-NS are disassociated and separated at the NC monolayer - metal interface due to the difference in the workfunctions. As a result, the proposed LS-NS platforms perform as highly sensitive photosensors, despite using a single NC monolayer, which makes the device semi-transparent and reduces the noise generation Furthermore, because of the band gap tunability, it is possible to construct cascaded NC layers with a designed band gap gradient where the NC diameters monotonically change. Here we present the first account of exciton funneling in an active device, which leads to significant performance improvement in the device. We show highly photosensitive NC skins employing the exciton funneling across the multiple layers of NC film. To further enhance the device photosensitivity performance, we demonstrate embedding plasmonic nanoparticles into the light-sensitive skins of the NCs. In addition, we exhibit the LS-NS device sensitivity enhancement utilizing the device architecture of semi-transparent tandem skins, the addition of TiO2 layer for increased charge carrier dissociation, and the phenomenon of multiexciton generation in infrared NCs. With fully sealed NC monolayers, LS-NS is found to be highly stable under ambient conditions, promising for low-cost large-area UV/visible sensing in windows and facades of smart buildings. We believe the findings presented in this thesis have significant implications for the future design of photosensing platforms and for moving toward next generation large-surface light-sensing platforms.en_US
dc.description.statementofresponsibilityAkhavan, Shahaben_US
dc.format.extentxviii, 100 leaves, illustrations, graphicsen_US
dc.publisherBilkent Universityen_US
dc.subjectQuantum dotsen_US
dc.subjectplasmonic nanostructuresen_US
dc.subjectmultiexciton generationen_US
dc.subjectlight sensingen_US
dc.subjecttime resolved fluorescenceen_US
dc.subject.lccQC611.8.N33 A44 2013en_US
dc.subject.lcshNanocrystals--Optical properties.en_US
dc.subject.lcshSemiconductors--Optical properties.en_US
dc.subject.lcshQuantum dots.en_US
dc.subject.lcshExciton theory.en_US
dc.subject.lcshPlasmons (Physics)en_US
dc.titleNovel light-sensitive nanocrystal skinsen_US
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