Browsing by Author "Sarma, Monima"

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A demonstration of solid-state white light-emitting electrochemical cells using the integrated on-chip plasmonic notch filters
(2016)
Lee, Ya-Ju
;
Lin, Chia-Ching
;
Lee, Hsiao-Chin
;
Yao, Yung-Chi
;
Sarma, Monima
In this study, we demonstrate solid-state white light-emitting electrochemical cells (LECs) using an integrated plasmonic notch filter to tailor the electroluminescence (EL) spectrum of non-doped blue-green emissive material. The plasmonic notch filter is composed of randomly distributed silver nanoparticles (Ag-NPs) embedded in the anode contact of indium tin oxide (ITO). This plasmonic notch filter strongly absorbs green light due to local surface plasmon (LSP) resonance of the Ag-NPs embedded in ITO. Thus, the emission green light of the solid-state LEC is strongly suppressed, leaving the blue and red light output to generate a white EL emission. Moreover, the duration of white EL can be maintained for a longer time under operation, which overcomes the issues regarding the short lifetime of white EL generated by the microcavity effect. In addition, the Ag-NPs can be readily fabricated by the thermal annealing of Ag film, which is compatible with current fabrication technologies typically used in light-emitting diode (LED) industry. Therefore, solid-state white LECs using an integrated on-chip plasmonic notch filter have great potential for applications in solid-state lighting.
Adjusting Color Temperature of Electroluminescence from White Light-Emitting Electrochemical Cells by Laser-Scanned Annealing of Nanoparticles
(2017-01-01)
Lee, Hsiao-Chin
;
Chiang, Chien-Ming Fan
;
Wu, Po-Yi
;
Yao, Yung-Chi
;
Sarma, Monima
Color temperature of electroluminescence from white light-emitting electrochemical cells can be adjusted by locally laser-scanned thermal annealing on a semi-continuous thin Ag film embedded between indium tin oxide anode and glass substrate. The proposed technique offers programmable versatility to control white electroluminescence and is compatible with display manufacturing technologies.
Dynamically tuning the correlated color temperature of white light-emitting electrochemical cells with electrochromic filters
(2017-09-01)
Chiou, Bo-Ruei
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Lee, Hsiao-Chin
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Jang, Yea-Fen
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Yang, Zu-Po
;
Wang, Yao-Chin
Recently, white solid-state light-emitting electrochemical cells (LECs) have drawn great attention since they exhibit advantages such as low-voltage operation, compatibility with solution processes and employing inert cathode metals. Since different correlated color temperatures (CCTs) of background illumination are necessary for various lighting applications, a real-time tunable CCT of white LECs would be highly desired in modern smart lighting systems. In this work, a widely and dynamically tuning CCT (>10000 K) of white LEC is demonstrated by employing an electrochromic device (ECD) as a real-time controllable color filter. By increasing the applied bias on the ECD to attenuate more the red parts of white EL from the white LEC, the LEC-based white light source becomes more bluish and, in consequence, shows higher CCT. This proposed LEC-based white light source with the characteristics of wide CCT range and real-time tunability is suitable for most lighting applications and modern smart lighting systems. (C) 2017 Elsevier B.V. All rights reserved.
Improving color saturation of blue light-emitting electrochemical cells by plasmonic filters
(2017-12-01)
Chiang, Chien-Ming Fan
;
Chang, Bo-Ren
;
Lee, Ya-Ju
;
Sarma, Monima
;
Yang, Zu-Po
In consideration of the advantages of light-emitting electrochemical cells (LECs), it is desired to develop the saturated blue LECs for LEC display, which is hindered by the features of broad emission spectrum and emission peak not short enough. In this study, we demonstrated a novel method to improve blue saturation of the sky-blue LECs by engineering its emission spectrum through the plasmonic filters. These plasmonic filters composed of randomly distributed silver nanoparticles (Ag-NPs) can absorb the green and red emission tail of the sky-blue LECs due to localized surface plasmon resonance (LSPR). The LSPR wavelengths of Ag-NPs are tuned by manipulating the effective refractive index of materials around Ag-NPs through the accurate control of the TiO2 thickness using atomic layer deposition technique. By integrating with the plasmonic filters, the CIE1931 coordinate of the blue LECs can approach to (0.14, 0.22), which is comparable to or even better than the reported bluest values of blue LECs. Combination with the green and red LECs, the color gamut increases from 34% (without filters) to 54% of National Television System Committee (NTSC) color gamut, corresponding to 1.6 times enhancement. In addition, the blue LECs integrated with plasmonic filters still have better efficiency than those of the reported bluest LECs. (C) 2017 Elsevier B.V. All rights reserved.
Laser-Scanned Programmable Color Temperature of Electroluminescence from White Light-Emitting Electrochemical Cells
(2016-11-23)
Lee, Hsiao-Chin
;
Chiang, Chien-Ming Fan
;
Wu, Po-Yi
;
Yao, Yung-Chi
;
Sarma, Monima
Recently, the control of correlated color temperature (CCT) of artificial solid-state white-light sources starts to attract more attention since CTs affect human physiology and health profoundly. In this work, we proposed and demonstrated a method that can widely tune the CCTs of electroluminescence (EL) from white-light-emitting electrochemical cells (LECs) by employing plasmonic filters. These integrated on-chip plasmonic filters are composed of semicontinuous thin Ag film or Ag nanoparticles (NPs) both included in the indium tin oxide anode contact, which have different characteristics of plasmonic resonant absorptions that can tune the EL spectra of white LECs. The CCTs of EL from white LECs integrated with semicontinuous thin Ag film and randomly distributed Ag NPs are 5778 and 2350 K, respectively. A commercially available laser scanning system was used to locally thermal anneal the semicontinuous thin Ag film to form the randomly distributed Ag NPs on the scanned areas. Hence, these two kinds of filters can be integrated on the same chip of white LEC, giving more freedom to control the CCTs of white EL and more potential applications. In addition, the laser scanning system used here is quite often used in display manufactures so that our proposed method can be immediately adopted by the light-emitting diode industry.
Solid-state white light-emitting electrochemical cells based on scattering red color conversion layers
(2015-01-01)
Lin, Guan-Rung
;
Cheng, Jing-Rong
;
Wang, Chi-Wei
;
Sarma, Monima
;
Chen, Hsiao-Fan
Solid-state white light-emitting electrochemical cells (LECs) based on ionic transition metal complexes are capable of generating efficient white electroluminescence (EL). Recently, blue-emitting LECs combined with embedded red color conversion layers (CCLs), which were inserted between indium tin oxide (ITO) and a glass substrate, have been reported to offer an external quantum efficiency (EQE) >12%. However, the output spectrum of EL from such white LECs changed with time due to the altered microcavity effect when the recombination zone was moving. Furthermore, the device efficiency should be further improved to realize practical applications. In this work, TiO2 nanoparticles (NPs) of two sizes are incorporated into red CCLs to improve device performance. Large NPs (250 nm) can scatter and redirect the light passing through red CCLs and further enhance the extracted light. Small NPs (25 nm) increase the refractive index of red CCLs and raise the amount of light intensity in the evanescent tail of the waveguide mode near the ITO layer. Therefore, more trapped light in the evanescent tail of the waveguide mode can be recycled to the external mode by scattering. The peak EQE and power efficiency of white LECs employing scattering red CCLs reach 20.0% and 39.5 lm W-1, respectively. Furthermore, with scattering NPs to average the EL in different directions, white EL is almost invariant with time. These results show that blue-emitting LECs combined with scattering red CCLs would be effective to provide efficient and stable white EL.
Tuning the Color Temperature of White-Light-Emitting Electrochemical Cells by Laser-Scanning Perovskite-Nanocrystal Color Conversion Layers
(2018-04-01)
Wu, Wen-Kuang
;
Wang, Cheng-Ming
;
Chan, Ming-Che
;
Lien, Jiun-Yi
;
Su, Yong-Ming
The development of white-light-emitting electrochemical cells (LECs) has attracted great attention owing to their numerous advantages. Recently, perovskite materials have also shown many outstanding optoelectronic properties in light absorption and emission, and hence they are suitable for serving as the color conversion layers (CCLs) in solid-state white-light-emitting diodes (LEDs). Here, white LECs were fabricated by integrating non-doped blue-green LECs with CCLs made of a single composition of perovskite nanocrystal (NCs). Moreover, the correlated color temperatures (CCTs) of the white LECs can be tuned by modifying the optical properties of the perovskite NCs, in the same way as so as the color conversion properties of CCLs are tuned, through laser scan. By controlling the laser power, scanning number, and duty cycle of the scanned grating patterns on perovskite-NC CCLs, the CCTs of the white LECs can be tuned from 2502 K to nearly 4300 K. Since this method is much different from that used with conventional CCLs, which use multiple compositions of perovskite NCs to produce white light, the inherent anion-exchange issue of perovskite NCs can be avoided.