Enhancing device efficiencies of solid-state white light-emitting electrochemical cells by employing waveguide coupling

Cheng, Chia Yu; Wang, Chi Wei; Cheng, Jing Rong; Chen, Hsiao-Fan; Yeh, Yun Shiuan; Su, Hai‐Ching; Chang, Chih‐Hao; Wong, Ken‐Tsung

doi:10.1039/c5tc00765h

Cited by 45 publications

(34 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Furthermore, in addition to Au nanoparticles and Ag nanorods dispersed in interlayers, Au nanoparticles and Ag nanoparticles that adhere to the surface of MHP NCs can induce surface plasmon resonance and maximize the light extraction from PeLEDs toward the outside. We also expect that the combination of high‐index electrode and low‐index HIL, optimization of electrode or interlayer thicknesses, corrugated device structure, and light‐outcoupling layers would help to extract the light and increase the EL efficiency of PeLEDs. Optical simulation may assist to optimize the device structure to maximize the outcoupling efficiency, as it did in OLEDs…”

Section: Discussionmentioning

confidence: 99%

Strategies to Improve Luminescence Efficiency of Metal‐Halide Perovskites and Light‐Emitting Diodes

2018

View full text Add to dashboard Cite

emitters (FWHM ≈ 30 nm; color gamut ≈100% in NTSC standard and <90% in Rec. 2020 standard). [11][12][13][14][15] MHPs are composed of three atoms or molecules in simple crystal structures, ABX 3 or A 2 BX 4 , where A is an organic ammonium (OA, e.g., methylammonium (MA; CH 3 NH 3 + ) and formamidinium (FA; CH(NH 2 ) 2 + )) or an alkali metal cation (e.g., Cs + ), B is a transition metal cation (e.g., Au 2+ , Sn 2+ , Mn 2+ , and Pb 2+ ), and X is a halide anion (I − , Br − , and Cl − ). In 3D ABX 3 cubic crystal structure, one B cation is coordinated to the six halide anions in a corner of BX 6 octahedral con figuration and A is located in the octahe dral voids. Although bandgap formation mechanism of MHP crystals is still under debate, electronic structure of MHP crys tals is mainly contributed by the inor ganic BX 6 octahedra rather than by the A cations; [16][17][18] these studies indicate that emission wavelength λ of MHP emitters can easily be tuned (380 ≤ λ ≤ 1000 nm) by totally or partially replacing B cations or X anions. Perov skite crystal structure is also affected by Asite cations due to hydrogen bonding and vibrational coupling between BX 3 − and A + , so bandgap and concomitant λ of MHPs can be controlled by tuning the Asite cations. [19,20] These emission spectra with high color purity and wide λ tunability do not depend on the size of grains or crystals of MHP emitters when their dimen sion is larger than exciton Bohr diameter D B ; [21,22] this size independent high color purity of MHPs is particularly suited as a vivid natural color emitter in future display technology.Because of their unique crystal structure (e.g., ionic bonding) and bandgap formation mechanism, MHPs have balanced and high charge carrier mobility (e.g., both electron and hole mobility ≈ 1000 cm 2 (V s) −1 in CsPbBr 3 single crystals [23] ) and have comparable energy level to those of organic semiconduc tors. [24] Furthermore, MHP emitters have low material cost and good compatibility with diverse solution processes to synthe size MHP crystals; these are great advantages of MHPs to mass production and commercialization.In the early 1990s, several researchers tried to fabricate the MHP lightemitting diodes (PeLEDs) by using layered MHP emitters as an emitting layer (EML). [25,26] However, MHPs showed low photoluminescence quantum efficiency (PLQE), and yielded bright electroluminescence (EL) only at cryogenic temperature, which may be ascribed to immature MHP crystalli zation processes, ineffective confinement of electrons and holes, Metal-halide perovskites (MHPs) are well suited to be vivid natural color emitters due to their superior optical and electrical properties, such as narrow emission linewidths, easily and widely tunable emission wavelengths, low material cost, and high charge carrier mobility. Since the first development of MHP light-emitting diodes (PeLEDs) in 2014, many researchers have tried to understand the properties of MHP emitters and the limitations to luminescence efficiency (LE) of PeLEDs, and have devoted ...

show abstract

Section: Discussionmentioning

confidence: 99%

Strategies to Improve Luminescence Efficiency of Metal‐Halide Perovskites and Light‐Emitting Diodes

2018

View full text Add to dashboard Cite

show abstract

“…A large amount of waveguided EL is still trapped inside the ITO layer. To extract that EL, waveguide coupling was used in white LECs based on complex 1 doped with 0.2 % [Ir(ppy) 2 (biq)]PF 6 (complex 2 ; where ppy is 2‐phenylpyridine, and biq is 2,2′‐biquinoline) . As shown in Figure , two TPR layers doped with TiO 2 NPs were inserted between the ITO layer and glass substrate.…”

Section: Light Extractionmentioning

confidence: 99%

“… Structure of the LEC using waveguide coupling. The optical field distributions of the EL trapped in ITO and bottom waveguide layers are shown as dashed lines …”

Section: Light Extractionmentioning

confidence: 99%

Optical Techniques for Light‐Emitting Electrochemical Cells

2018

ChemPlusChem

Self Cite

View full text Add to dashboard Cite

The concept of solid‐state light‐emitting electrochemical cells (LECs), proposed in 1995, opened a new field in display and lighting technologies. The key advantage of this technology derives from a single emissive layer containing an emissive material and an ionic salt. Mobile ions in the emissive layer induce electrochemical doping at electrodes and thus the operation voltage can be reduced even if using air‐stable electrodes. Since the first demonstration of LECs, many materials‐oriented efforts have been made in improving device performance of LECs. However, some difficulties arising from material properties limit further optimizing the device characteristics of LECs. Recently, optical techniques have been shown to achieve better device properties without using new materials. Light extraction techniques recycle the light trapped in layered device structure and thus enhance the light output and efficiency of LECs. Recombination zone probing techniques offer direct evidence of carrier balance in LECs and is helpful in optimizing device performance. Spectral filtering based on microcavity effects and localized surface plasmon resonance from metal nanoparticles have the advantages of easy fabrication and compatibility with device processing of LECs. This Minireview provides an overview of the three categories of recent advances in optical techniques for LECs.

show abstract

“…However, the electrochromic device, serving an optical filter, is bulky. In comparison to these novel methods to produce white LECs and control CCT, conventional methods using color conversion layers (CCLs) to generate white LECs is cost‐effective (because no expensive equipment is needed for fabrication) and the LECs are still thin enough (especially in comparison with the electrochromic device) . However, like the host–guest method, careful control of the concentration of the red dye in CCLs is needed.…”

Section: Introductionmentioning

confidence: 99%

Tuning the Color Temperature of White‐Light‐Emitting Electrochemical Cells by Laser‐Scanning Perovskite‐Nanocrystal Color Conversion Layers

Wang

Chan

et al. 2017

ChemPlusChem

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Enhancing device efficiencies of solid-state white light-emitting electrochemical cells by employing waveguide coupling

Abstract: Device efficiency of white LECs can be enhanced by recycling the trapped EL in the ITO layer to the forward direction.

Cited by 45 publications

References 41 publications

Strategies to Improve Luminescence Efficiency of Metal‐Halide Perovskites and Light‐Emitting Diodes

Strategies to Improve Luminescence Efficiency of Metal‐Halide Perovskites and Light‐Emitting Diodes

Optical Techniques for Light‐Emitting Electrochemical Cells

Tuning the Color Temperature of White‐Light‐Emitting Electrochemical Cells by Laser‐Scanning Perovskite‐Nanocrystal Color Conversion Layers

Contact Info

Product

Resources

About