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    ItemOpen Access
    Large-area semi-transparent light-sensitive nanocrystal skins
    (Optical Society of America, 2012) Akhavan, S.; Guzelturk, B.; Sharma, V. K.; Demir, Hilmi Volkan
    We report a large-area, semi-transparent, light-sensitive nanocrystal skin (LS-NS) platform consisting of single monolayer colloidal nanocrystals. LS-NS devices, which were fabricated over areas up to 48 cm(2) using spray-coating and several cm-squares using dip-coating, are operated on the principle of photogenerated potential buildup, unlike the conventional charge collection. Implementing proof-of-concept devices using CdTe nanocrystals with ligand removal, we observed a substantial sensitivity enhancement factor of similar to 73%, accompanied with a 3-fold faster response time (<100 ms). With fully sealed nanocrystal 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. (C) 2012 Optical Society of America
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    ItemOpen Access
    Plasmonic backcontact grating for P3HT:PCBM organic solar cells enabling strong optical absorption increased in all polarizations
    (Optical Society of America, 2011) Sefunc, M. A.; Okyay, Ali Kemal; Demir, Hilmi Volkan
    In P3HT:PCBM based organic solar cells we propose and demonstrate numerically plasmonic backcontact grating architectures for strong optical absorption enhanced in both transverse-magnetic and transverse-electric polarizations. Even when the active material is partially replaced by the metallic grating (without increasing the active layer film thickness), we show computationally that the light absorption in thin-film P3HT:PCBM is increased by a maximum factor of similar to 21% considering both polarizations under AM1.5G solar radiation and over a half-maximum incidence angle of 45 degrees (where the enhancement drops to its half) compared to the same cell without a grating. This backcontact grating outperforms the typical plasmonic grating placed in PEDOT:PSS layer. (C)2011 Optical Society of America.
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    ItemOpen Access
    Simultaneous enhancement of electron overflow reduction and hole injection promotion by tailoring the last quantum barrier in InGaN/GaN light-emitting diodes
    (AIP Publishing, 2014-04-24) Kyaw, Z.; Zhang Z.-H.; Liu W.; Tan S.T.; Ju, Z. G.; Zhang, X. L.; Ji Y.; Hasanov N.; Zhu B.; Lu S.; Zhang, Y.; Teng, J. H.; Wei, S. X.; Demir, Hilmi Volkan
    A three-step graded undoped-InGaN layers embedded between the GaN last quantum barrier layer and the p-AlGaN electron blocking layer was proposed and its effect on the performance of InGaN/GaN light-emitting diodes was investigated both experimentally and theoretically. In the proposed structure, the electron leakage is found to be effectively reduced, while the hole injection efficiency is simultaneously increased significantly, hence enabling a greatly enhanced radiative recombination rate within the active region. As a result, improvements of 12.25% in the optical output power and 11.98% in the external quantum efficiency are obtained from the proposed device with the respect to the reference device.