Browsing by Subject "Light-emitting diode"

Now showing 1 - 5 of 5

Open Access
Color-enrichment semiconductor nanocrystals for biorhythm-friendly backlighting
(De Gruyter, 2018) Erdem, T.; Demir, Hilmi Volkan
Nanocrystals (NCs) offer great opportunities for developing novel light-emitting devices possessing superior properties such as high quality indoor lighting, efficient outdoor lighting, and display backlighting with increased color definition. The narrow-band emission spectra of these materials also offer opportunities to protect the human daily biological rhythm against the adverse effects of display backlighting. For this purpose, here we address this problem using color converting NCs and analyzed the effect of the NC integrated color converting light-emitting diode (NC LED) backlight spectra on the human circadian rhythm. We employed the three existing models including the circadian light, the melanopic sensitivity function, and the circadian effect factor by simultaneously satisfying the National Television Standards Committee (NTSC) requirements. The results show that NC LED backlighting exhibits (i) 33% less disruption on the circadian cycle if the same color gamut of the commercially available YAG:Ce LED is targeted and (ii) 34% wider color gamut while causing 4.1% weaker disruption on the circadian rhythm compared to YAG:Ce LED backlight if the NTSC color gamut is fully reproduced. Furthermore, we found out that blue and green emission peaks have to be located at 465 with 30 nm bandwidth and at 535 nm with 20 nm bandwidth, respectively, for a circadian rhythm friendly design while the red component offers flexibility around the peak emission wavelength at 636 nm as opposed to the requirements of quality indoor lighting. These design considerations introduced as a new design perspective for the displays of future will help avoiding the disruption of the human circadian rhythm.
Open Access
High-performance deep red colloidal quantum well light-emitting diodes enabled by the understanding of charge dynamics
(American Chemical Society, 2022-07-11) Hu, S.; Shabani, Farzan; Liu, B.; Zhang, L.; Guo, M.; Lu, G; Zhou, Z.; Wang, J.; Huang, J.C.; Min, Y.; Xue, Q.; Demir, Hilmi Volkan; Liu, C.
Colloidal quantum wells (CQWs) have emerged as a promising family of two-dimensional (2D) optoelectronic materials with outstanding properties, including ultranarrow luminescence emission, nearly unity quantum yield, and large extinction coefficient. However, the performance of CQWs based light-emitting diodes (CQW-LEDs) is far from satisfactory, particularly for deep red emissions (≥660 nm). Herein, high efficiency, ultra-low-efficiency roll-off, high luminance, and extremely saturated deep red CQW-LEDs are reported. A key feature for the high performance is the understanding of charge dynamics achieved by introducing an efficient electron transport layer, ZnMgO, which enables balanced charge injection, reduced nonradiative channels, and smooth films. The CQW-LEDs based on (CdSe/CdS)@(CdS/CdZnS) ((core/crown)@(colloidal atomic layer deposition shell/hot injection shell)) show an external quantum efficiency of 9.89%, which is a record value for 2D nanocrystal LEDs with deep red emissions. The device also exhibits an ultra-low-efficiency roll-off and a high luminance of 3853 cd m−2. Additionally, an exceptional color purity with the CIE coordinates of (0.719, 0.278) is obtained, indicating that the color gamut covers 102% of the International Telecommunication Union Recommendation BT 2020 (Rec. 2020) standard in the CIE 1931 color space, which is the best for CQW-LEDs. Furthermore, an active-matrix CQW-LED pixel circuit is demonstrated. The findings imply that the understanding of charge dynamics not only enables high-performance CQW-LEDs and can be further applied to other kinds of nanocrystal LEDs but also is beneficial to the development of CQW-LEDs-based display technology and related integrated optoelectronics.
Open Access
InGaN stress compensation layers in InGaN/GaN blue LEDs with step graded electron injectors
(Academic Press, 2018) Sheremet, V.; Gheshlaghi, N.; Sözen, M.; Elçi, M.; Sheremet, N.; Aydınlı, A.; Altuntaş, I.; Ding, K.; Avrutin, V.; Özgür, Ü.; Morkoç, H.
We investigate the effect of InGaN stress compensation layer on the properties of light emitting diodes based on InGaN/GaN multiple quantum well (MQW) structures with step-graded electron injectors. Insertion of an InGaN stress compensation layer between n-GaN and the step graded electron injector provides, among others, strain reduction in the MQW region and as a result improves epitaxial quality that can be observed by 15-fold decrease of V-pit density. We observed more uniform distribution of In between quantum wells in MQW region from results of electro- and photoluminescence measurement. These structural improvements lead to increasing of radiant intensity by a factor of 1.7-2.0 and enhancement of LED efficiency by 40%.
Open Access
Management of electroluminescence from silver-doped colloidal quantum well light-emitting diodes
(Cell Press, 2022-05-18) Liu, Baiquan; Sharma, Manoj; Yu, Junhong; Wang, Lin; Shendre, Sushant; Sharma, Ashma; Izmir, Merve; Delikanlı, Savaş; Altıntaş, Yemliha; Dang, Cuong; Sun, Handong; Demir, Hilmi Volkan
Impurity doping is a promising strategy to afford colloidal nanocrystals exhibiting novel optical, catalytic, and electronic characteristics. However, some significant properties of noble metal-doped nanocrystals (NMD-NCs) remain unknown. Here, we report the electroluminescence (EL) from NMD-NCs. By doping silver impurity into cadmium selenide colloidal quantum wells (CQWs), dual-emission emitters are achieved and a light-emitting diode (LED) with a luminance of 1,339 cd m−2 is reported. In addition, the proposed energy gap engineering to manage exciton recombination is a feasible scheme for tunable EL emissions (e.g., the dopant emission is tuned from 606 to 761 nm). Furthermore, an organic-inorganic hybrid white LED based on CQWs is realized, reaching a color rendering index of 82. Moreover, flexible CQW-LEDs are reported. The findings present a step to unveil the EL property of NMD-NCs, which can be extended to other noble metal impurities, and pave the pathway for NMD-NCs as a class of electronic materials for EL applications. © 2022 The Authors
Open Access
Nanocrystal light-emitting diodes based on type II nanoplatelets
(Elsevier BV, 2018) Liu, B.; Delikanli S.; Gao, Y.; Dede, D.; Gungor K.; Demir, Hilmi Volkan
Colloidal semiconductor nanoplatelets (NPLs) have recently emerged as a new family of semiconductor nanocrystals with distinctive structural and electronic properties originating from their atomically flat architecture. To date, type II NPLs have been demonstrated to possess great potential to optoelectronic applications, such as solar cells and lasers. Herein, nanocrystal light-emitting diodes (LEDs) based on type II NPLs have been developed. The photoluminescence quantum yield of these used type II NPL (CdSe/CdSe0.8Te0.2 core/crown) is close to 85%. By exploring an effective inverted structure with the dual hole transport layer, the NPL-LEDs exhibit i) a turn-on voltage of 1.9 V, ii) a maximum luminance of 34520 cd m−2, iii) an EQE of 3.57% and a PE of 9.44 lm W−1. Compared with previous NPL-based LEDs, the performance of our devices is remarkably enhanced. For example, the luminance is 350-fold higher than the best inverted NPL-based LED. The findings may not only represent a significant step for NPL-based LEDs, but also unlock a new opportunity that this class of type II NPLs materials are promising for developing high-performance LEDs.