Browsing by Author "Bozkaya, Taylan"
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Item Open Access Light-sensitive monolayer-thick nanocrystal skins of face-down self-oriented colloidal quantum wells(Royal Society of Chemistry, 2023-10-20) Bozkaya, Taylan; Işık, Furkan; Bozkaya, İklim; Delikanlı, Savaş; Ünal, Emre; Demir, Hilmi VolkanColloidal quantum wells (CQWs), a quasi-two-dimensional, atomically-flat sub-family of semiconductor nanocrystals, are well suited to produce excellent devices for photosensing applications thanks to their extraordinarily large absorption cross-sections. In this work, we propose and demonstrate a new class of light-sensitive nanocrystal skins (LS-NS) that employ a monolayer of face-down orientation-controlled self-assembled CQWs as the active absorbing layer in the UV-visible range. This CQW LS-NS platform enables non-conventional photosensing operation that relies on the strong optical absorption of the monolayered assembly of CQWs and the subsequent photogenerated potential build-up across the device, allowing for self-powered operation. Here such self-oriented CQWs reduce the surface roughness in their monolayer-thick film, essential to high device performance. Owing to their ease of fabrication and low cost, these devices hold great promise for large-scale use in semi-transparent photosensing surfaces.Item Unknown Monolayer-thick light-sensitive nanocrystal skins of oriented colloidal quantum wells(Bilkent University, 2023-05) Bozkaya, TaylanColloidal quantum wells (CQWs), a two-dimensional member of semiconductor nanocrystals, featuring very tight vertical quantum confinement, possess giant oscillator strengths. Also, CQWs exhibit remarkably large absorption cross-sections, thanks to their oscillator strengths combined with their laterally large geometries. Additionally, as a powerful tool of fabrication, CQWs lend themselves to be conveniently self-assembled into monolayer-thick films in a single orientation of our choice: either face-down (lying down on their large lateral surfaces and side by side leaving no large gap between them similar to a mosaic pattern) or edge-up (standing up on their thin edges and facing each other in a very dense superstructure formation of repeating chains). In this thesis, to make use of the attractive absorption properties of CQWs and leverage on our ability to construct their orientation-controlled self-assemblies, we show the first account of monolayer-thick light-sensitive nanocrystal skins (LS-NS) that employ self-oriented CQWs as their active absorptive layer. These CQW LS-NS devices operate on the principle of strong optical absorption of the monolayered assembly of CQWs and the subsequent photogenerated potential build-up across their strongly capacitive thin device for sensing in the visible to ultraviolet. Such oriented CQWs in the LS-NS device architecture yield profoundly reduced surface roughness in their monolayer-thick films, essential to high device performance. Here, specifically, we developed and demonstrated two groups of LS-NS devices: one group consisting of all face-down oriented CQWs and the other, of all edge-up ones. We systematically studied their photocharging effect, spectral sensitivity and decay times. We observed in all LS-NS devices that the spectral sensitivity complies with the first (heavy-hole) and second (light hole) excitonic peaks of the absorption of the CQWs. We also found that, as the excitation power is increased, the peak photovoltage readout increases while the sensitivity decreases. The photocharging effect was further observed as the excitation was turned off. Finally, using the edge-up orientation, we identified a profound peak photovoltage signal enhancement. These findings of the thesis indicate that the proposed LS-NS devices of the orientation-controlled CQW monolayers hold great promise for applications in photos-sensing facades over larger surfaces.Item Unknown On the rational design of core/(multi)-Crown Type-II Heteronanoplatelets(American Chemical Society, 2023-05-09) Demir, Hilmi Volkan; Delikanlı, Savaş; Canımkurbey, Betül; Hernández-Martínez, P. L.; Shabani, Farzan; Işık, Ahmet Tarık; Özkan, İlayda; Bozkaya, İklim; Bozkaya, Taylan; Işık, Furkan; Durmuşoglu, E. G.; İzmir, M.; Hakan, AkgünSolution-processed two-dimensional nanoplatelets (NPLs) allowing lateral growth of a shell (crown) by not affecting the pure confinement in the vertical direction provide unprecedented opportunities for designing heterostructures for light-emitting and -harvesting applications. Here, we present a pathway for designing and synthesizing colloidal type-II core/(multi-)crown hetero-NPLs and investigate their optical properties. Stoke's shifted broad photoluminescence (PL) emission and long PL lifetime (∼few 100 ns) together with our wavefunction calculations confirm the type-II electronic structure in the synthesized CdS/CdSe1-xTexcore/crown hetero-NPLs. In addition, we experimentally obtained the band-offsets between CdS, CdTe, and CdSe in these NPLs. These results helped us designing hetero-NPLs with near-unity PL quantum yield in the CdSe/CdSe1-xTex/CdSe/CdS core/multicrown architecture. These core/multicrown hetero-NPLs have two type-II interfaces unlike traditional type-II NPLs having only one and possess a CdS ending layer for passivation and efficient suppression of stacking required for optoelectronic applications. The light-emitting diode (LED) obtained using multicrown hetero-NPLs exhibits a maximum luminance of 36,612 cd/m2and external quantum efficiency of 9.3%, which outcompetes the previous best results from type-II NPL-based LEDs. These findings may enable designs of future advanced heterostructures of NPLs which are anticipated to show desirable results, especially for LED and lasing platforms. © 2023 American Chemical Society. All rights reserved.