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Four emitters based on the naphthyridine acceptor moiety and various donor units exhibiting thermally activated delayed fluorescence (TADF) were designed and synthesized. The emitters exhibited excellent TADF properties with a small ΔE ST and a high photoluminescence quantum yield. A green TADF organic light-emitting diode based on 10-(4-(1,8-naphthyridin-2-yl)phenyl)-10H-phenothiazine exhibited a maximum external quantum efficiency of 16.4% with Commission Internationale de L'éclairage coordinates of (0.368, 0.569) as well as a high current and power efficiency of 58.6 cd/A and 57.1 lm/W, respectively. The supreme power efficiency is a record-high value among the reported values of devices with naphthyridine-based emitters. This results from its high photoluminescence quantum yield, efficient TADF, and horizontal molecular orientation. The molecular orientations of the films of the host and the host doped with the naphthyridine emitter were explored by angle-dependent photoluminescence and grazing-incidence small-angle X-ray scattering (GIWAXS). The orientation order parameters (ΘADPL) were found to be 0.37, 0.45, 0.62, and 0.74 for the naphthyridine dopants with dimethylacridan, carbazole, phenoxazine, and phenothiazine donor moieties, respectively. These results were also proven by GIWAXS measurement. The derivative of naphthyridine and phenothiazine was shown to be more flexible to align with the host and to show the favorable horizontal molecular orientation and crystalline domain size, benefiting the outcoupling efficiency and contributing to the device efficiency.

In this study, we develop a steady state and time-dependent exciton diffusion model including singlet and triplet excitons coupled with a modified Poisson and drift-diffusion solver to explain the mechanism of hyper triplet-triplet fusion (TTF) organic light-emitting diodes (OLEDs). Using this modified simulator, we demonstrate various characteristics of OLEDs, including the J-V curve, internal quantum efficiency, transient spectrum, and electric profile. This solver can also be used to explain the mechanism of hyper-TTF-OLEDs and analyze the loss from different exciton mechanisms. Furthermore, we perform additional optimization of hyper-TTF-OLEDs that increases the internal quantum efficiency by approximately 33% (from 29% to 40%).

Triplet is like a double-edged knife, that can degrade or benefit the electroluminescence performances of organic light-emitting diodes (OLEDs), especially for blue light. Therefore, efficient triplet harvesting for triplet-triplet fusion (TTF) fluorescence emission is essential to achieving high-efficiency blue TTF-OLEDs, which are known for their excellent reliability. This study presents a hyper-TTF mechanism for maximizing triplet exciton usage and avoiding triplet-polaron quenching to generate more photons through Dexter energy transfer (DET) and TTF processes. Specially, a triplet tank layer (TTL) was introduced adjacent to the TTF emitting layer (EML). Efficient carrier recombination and triplet generation are confined to the TTL of the device. Most triplets were observed to undergo DET from the TTL to the TTF EML; they subsequently became singlets exhibiting delayed fluorescence. Furthermore, the triplet-polaron quenching is suppressed by inhibiting hole into the TTF EML. A record-high TTF-OLED efficiency was achieved with an external quantum efficiency of 15.4%.

Developing a colloidal quantum-dot light-emitting device (QDLED) with high efficiency and good reliability is necessarily preliminary for the next-generation high-quality display application. Most QDLED reports are focused on efficiency improvement, but the device operational lifetime issue is less addressed and also the relevant degradation mechanisms. This study achieved a 1.72 times elongation in the operational lifetime and a 9 times improvement in the efficiency of QDLED by inserting a hole-transporting/electron-blocking poly(9-vinylcarbazole) (PVK) layer, which prevented operational degradation on poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-secbutylphenyl))-diphenylamine)] (TFB) hole-transporting layer and also confined the electron in the QD-emitting layer. Although the TFB/PVK HTL structure is a well-known pair to enhance the device performance, its detailed mechanisms were rarely mentioned, especially for relative operational lifetime issues. Herein, a new insight behind operational lifetime elongation of QDLED is disclosed through various fundamental experiments including steady-state photoluminescence, transient electroluminescence and single-carrier only devices. Evidently, other than QD degradation, this study found that the other crucial factor that decreased the device lifetime was TFB-HTL degradation using steady-state photoluminescence and transient electroluminescence analyses. The PVK electron-only device exhibited a stable voltage value when it was driven by fixed current, which also affirmed that PVK has excellent electron-stability characteristics.

This study reported the effects of electron transport layer (ETL) thickness on light extraction in corrugated organic light-emitting diodes (OLEDs) and each layer in OLEDs exhibited a periodical corrugated structure, which was determined by depositing thin films on a glass substrate with a nanoimprinted blazed grating structure. The insight is that light extraction in corrugated OLEDs significantly depends on the ETL thickness. Varying the ETL thickness changed the distribution of carrier recombination and led to exciton formation and optical interference, thereby resulting in different attribution of optical loss modes in OLEDs, which increased or even decreased light extraction and device efficiency. Trapped light extraction from the surface plasmon polariton (SPP) and waveguide (WG) modes was identified by splitting the light into transverse electric and transverse magnetic emissions. Thus, the contributions from the individual SPP and WG modes to the external quantum efficiency (EQE) were distinctly clarified by comparing the experimental results with the theoretical calculations. At the ETL thickness of 115 nm, the corrugated OLED exhibited a significantly enhanced (1.83-fold) EQE compared to the planar one due to the effective extraction of trapped light from the SPP and WG modes. The EQE was enhanced by 0.5%, wherein 0.39% came from the WG mode and 0.11% came from the SPP mode.

In this paper, a hardware implementation of a data hiding technique is proposed for efficient quality access control of images using lifting-based discrete wavelet transformation (DWT). Host image is decomposed into n-level wavelet tiles. A binary watermark image is transmuted and embedded into high–high DWT coefficients using adaptive dither modulation technique without self-noise suppression. The embedding of external information into the host image will degrade the visual quality. This feature may be utilized for access control. At the decoder side, an authorized user can enjoy superior quality image by extracting watermark bits using minimum distance decoding. Field-programmable gate array-based hardware architecture is proposed for real-time implementation of the scheme. The experiment is done over a large number of benchmark images, and the results are found to be superior to the related work which is present in the literature. It is also seen that (a) in real-time processing, the scheme saves 89.53% power than the related implementation found in the literature, and (b) a very high throughput of 23.8 MB/s is achieved for watermarking encoder and decoder, respectively, at a maximum operating frequency of 130.14 MHz for the processing of (512 × 512) sized images.

The efficient conversion of electron-hole (e-h) pairs into triplet excitons is a challenge for blue organic light-emitting diodes (OLEDs) based on triplet–triplet annihilation upconversion (TTAUC). The 25% fraction of e-h pairs that create singlet excitons represents a significant loss channel that can lead to parasitic red-shifted emission. In this study, an intermolecular intersystem crossing that relies on a “dark sensitizer” (DS) layer consisting of tris-(8-hydroxyquinoline)aluminum (Alq3) doped with tris[2-phenylpyridinato-C2,N]Iridium(III) (Ir(ppy)3) is demonstrated to enhance the TTAUC process. Carriers recombination and excitons generation are formed on Alq3 molecules. Alq3 singlet excitons are then quenched by the Ir(ppy)3 triplet state, followed by energy transfer to the Alq3 triplet state. The non-emissive, long-lived Alq3 triplets migrate from the sensitizer layer to an emitter layer where they undergo TTAUC to give blue fluorescence emission. This DS-TTAUC process promises no green emission from the Alq3. The efficiency of a blue OLED utilizing DS-TTAUC was improved by 34.2% compared to a standard TTAUC OLED. In addition, the device exhibited CIE coordinates of (0.15, 0.09). Furthermore, a high photoluminescence quantum yield fluorescence emitter is incorporated to enhance the singlet exciton emission in the emitter layer. A maximum external quantum efficiency of 7.54% can be achieved with recorded-high quantum yield of the TTAUC (ΦTTAUC) = 37.6% in solid state.

DG acknowledges funding from the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/177 . This research is/was funded by the European Regional Development Fund according to the supported activity ‘ Research Projects Implemented by World-class Researcher Groups ’ under Measure No. 01.2.2-LMT-K-718 . Ministry of Science and Technology (MOST), Taiwan , Grant No. MOST 106-2923-E-155-002-MY3 . This work was also supported by the Ministry of Education and Science of Ukraine (projects no. 0117U003908 and 0118U003862 ), and by the Olle Engkvist Byggmästare foundation (contract No. 189-0223 ). The quantum-chemical calculations were performed with computational resources provided by the High Performance Computing Center North (HPC2N) in Umeå, Sweden, through the project ‘‘Multiphysics Modeling of Molecular Materials” SNIC 2018-2-38., Flexible versus rigid molecular structures of donor-acceptor-donor type compounds are investigated with respect to efficiency of thermally activated delayed fluorescence (TADF) by theoretical and experimental approaches. Three highly efficient TADF emitters based on flexible diphenylsulfone and rigid dibenzothiophene-dioxide as acceptor units and di-tert-butyldimethyldihydroacridine as donor moiety were designed and synthesized. Despite they showed similar singlet-triplet splitting (0.01–0.02 eV) and high photoluminescence quantum yields in appropriate hosts, maximum external quantum efficiencies as different as 24.1 and 15.9/19.4% were obtained for organic light emitting devices based on these emitters with, respectively, flexible and rigid molecular structures. The high efficiency of the light-emitting compounds with the flexible molecular structure could be traced to the bi-configurational nature of the lowest singlet and triplet states resulting in higher spin-orbit coupling than for molecules with rigid structures. All derivatives showed bipolar charge transport character. High device efficiency with electron mobility of 3 × 10−5 cm2V−1s−1 and hole mobility of 1.3 × 10−4 cm2V−1s−1 at the electric field of 5 × 105 Vcm−1 was recorded for the layer of para-disubstituted diphenylsulfone with flexible molecular structure. This TADF emitter showed an excellent performance in the organic light emitting device, exhibiting a maximum current efficiency, power efficiency, and external quantum efficiency of 61.1 cdA-1, 64.0 lmW−1, and 24.1%, respectively., Ministry of Education and Science of Ukraine 0117U003908,0118U003862; Stiftelsen Olle Engkvist Byggmästare 189-0223; European Regional Development Fund 1.1.1.2/VIAA/1/16/177; European Regional Development Fund 01.2.2-LMT-K-718; Ministry of Science and Technology (MOST), Taiwan MOST 106-2923-E-155-002-MY3; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

The enhanced device performance of blue quantum dot light-emitting diodes (QD-LEDs) was demonstrated; a positive aging process was used to improve electron transport and suppress electroplex emission, which results from the interface between the QD-emitting layer and the ZnO electron-transporting layer (ETL). This electroplex interface functions as a low-energy recombination center, leading to energy loss and further decreasing the device performance. Without the positive aging process, the QD-LED exhibited poor electrical and electroluminescent (EL) characteristics, as well as an EL spectrum containing a strong electroplex emission with a peak at 635 nm. A positive aging process was applied by dripping a surface active reagent on the cathode before device encapsulation. The active reagent treatment led to suppression of the electroplex emission and enhanced device performance by promoting Al atoms into ZnO ETL to facilitate electron transport at the QD/ZnO interface. Furthermore, static positive aging was investigated by assessing the QD-LEDs at different storage times to observe the maturing process. After 409-hrs of maturing, the QD-LEDs exhibited an optimal device performance with favorable CEmax and EQEmax values of 6.2 cd/A and 8.7%, respectively. At a current density of 1 mA/cm2, the QD-LED exhibited a maximum overall efficiency enhancement factor of 7.1 after the positive aging process. In particular, electroplex suppression was correlated with the enhancement of device performance, caused by an upgraded QD/ZnO interface, formed during the positive aging process, benefits the electron transport.

In this study, we demonstrated a blue phosphorescent organic light-emitting diode (BPOLED) based on a host with two carbazole and one trizole (2CbzTAZ) moiety, 9,9′-(2-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)-1,3-phenylene)bis(9H-carbazole), that exhibits bipolar transport characteristics. Compared with the devices with a carbazole host (N,N’-dicarbazolyl-3,5-benzene, (mCP)), triazole host (3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole, (TAZ)), or a physical mixture of mCP:TAZ, which exhibit hole, electron, and bipolar transport characteristics, respectively, the BPOLED with the bipolar 2CbzTAZ host exhibited the lowest driving voltage (6.55 V at 10 mA/cm2), the highest efficiencies (maximum current efficiency of 52.25 cd/A and external quantum efficiency of 23.89%), and the lowest efficiency roll-off, when doped with bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) as blue phosphor. From analyses of light leakage of the emission spectra of electroluminescence, transient electroluminescence, and partially doped OLEDs, it was found that the recombination zone was well confined inside the emitting layer and the recombination rate was most efficient in a 2CbzTAZ-based OLED. For the other cases using mCP, TAZ, and mCP:TAZ as hosts, electrons and holes transported with different routes that resulted in carrier accumulation on different organic molecules and lowered the recombination rate.

In this paper, we investigate the carrier injection and transport characteristics in iridium(III)bis[4,6-(di-fluorophenyl)-pyridinato-N,C2']picolinate (FIrpic) doped phosphorescent organic light-emitting devices (OLEDs) with oxadiazole (OXD) as the bipolar host material of the emitting layer (EML). When doping Firpic inside the OXD, the driving voltage of OLEDs greatly decreases because FIrpic dopants facilitate electron injection and electron transport from the electron-transporting layer (ETL) into the EML. With increasing dopant concentration, the recombination zone shifts toward the anode side, analyzed with electroluminescence (EL) spectra. Besides, EL redshifts were also observed with increasing driving voltage, which means the electron mobility is more sensitive to the electric field than the hole mobility. To further investigate carrier injection and transport characteristics, FIrpic was intentionally undoped at different positions inside the EML. When FIrpic was undoped close to the ETL, driving voltage increased significantly which proves the dopant-assisted-electron-injection characteristic in this OLED. When the undoped layer is near the electron blocking layer, the driving voltage is only slightly increased, but the current efficiency is greatly reduced because the main recombination zone was undoped. However, non-negligible FIrpic emission is still observed which means the recombination zone penetrates inside the EML due to certain hole-transporting characteristics of the OXD.

In this paper, we investigated the effects of dopants on the electrical and optical characteristics of dichromatic and white organic light-emitting devices (OLEDs) with a double emitting layer (DEML). Such a DEML consisted of two host materials with bipolar transport characteristics doped with two distinct types of phosphorescent emitters. The host for EML1 (adjacent to the anode side) was N,N-dicarbazolyl-3,5-benzene (mCP), with a hole mobility higher than the electron mobility, whereas the host for EML2 (adjacent to the cathode side) was 2,2′-bis[5-phenyl-2-(1,3,4)oxadazolyl]biphenyl (OXD), with a higher electron mobility than the hole mobility. Phosphorescent blue emitters, 9% iridium(III)bis[4,6-di-fluorophenyl-pyridinato-N,C2]picolinate (FIrpic), and phosphorescent green emitters, 9% fac-tris(phenylpyridine) iridium [Ir(ppy)3], were doped into EML1 and EML2, respectively for dichromatic emission. In the dichromatic blue/green OLEDs, both the blue and green dopants helped to reduce the driving voltage. The dopants essentially played the role of carrier traps and recombination centers, from which the current density–voltage characteristics and electroluminescence (EL) spectra were derived. In this structure, EML1 and EML2 exhibited hole- and electron-rich bipolar transporting characteristics, respectively. Hence, the recombination was extended to the two EMLs, which reduced the efficiency roll-off and resulted in high efficiency levels even at high luminance levels. Through further incorporation of 0.5% of tris(2-phenylquinoline)iridium(III) [Ir(2-phq)3] into EML1, a white OLED with maximum current efficiency of 35.8 cd/A and quantum efficiency of 10.73% at 0.643 mA/cm2 was obtained. In this white OLED, the current efficiency decreased slightly by 2.51% from 35.8 cd/A at 230 cd/m2 to 34.9 cd/A at 1000 cd/m2. Carrier confinement was achieved at the D-EML interface, which not only contributed to the high current efficiency, but also resulted in stable color coordinates that varied a mere (−0.014, 0.004) from 100 to 10,000 cd/m2, without additional blocking layers between the two EMLs.

We report a corrugated structure to effectively extract the surface plasmon polaritons (SPP) and waveguiding modes in organic light-emitting diodes (OLEDs). This structure is formed by nano-imprint of blazed gratings. To study the optimum extraction condition in terms of grating pitches, we compare the light extraction efficiency of corrugated OLEDs with three kinds of pitches, showing a 42.00% external quantum efficiency (EQE) enhancement ratio with this internal structure. Due to the transfer of SPP and waveguiding modes into substrate mode, the EQE enhancement ratio can be further pushed to 103.02% by attaching a macrolens. The simulation verifies the experimental results and shows the extraction mechanism of the corrugated structure towards transverse electric (TE) and transverse magnetic (TM) waves. We foresee that this method is able to enhance the optical efficiency of devices for both mass-production OLED lighting and display in a cost-effective way.

In this paper, an organic light-emitting device (OLED) with low reflection for the entire visible range and at different viewing angles by using an absorptive and photo-sensitive material, N,N'-Bis(2,6-diisopropylphenyl)-1,7-bis(4-methoxyphenyl)perylene-3,4,9,10-tetracarboxydiimide (MPPDI), as a black layer (BL) structure was demonstrated. A semitransparent double-metal structure, Al/Ag, was used to reduce the driving voltage and enhance the destructive interference of the BL structure. Combined with the broad absorption band of the MPPDI, the reflectance of such a device shows a 12-times decrease compared to the conventional OLED. Also, a photocurrent enhancement effect was observed in our BL-OLED due to the photosensitive quality of the MPPDI.

To model the carrier transport in organic light-emitting diodes (OLEDs) with random dopant effects in the emitting layer, two-dimensional simulation was used. By including the Gaussian shape density of states and field-dependent mobility in the Poisson and drift-diffusion solver, the carrier transport, trapping in the dopant state, and radiative recombination were accurately modeled. To examine the model, the current-voltage characteristics of organic light-emitting devices were compared. The host material in the emitting layer was 2,2-bis(1-phenyl-1H-benzo[d]imidazol-2-yl)biphenyl (BImBP), which was doped with bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) at various concentrations. By including the random doping model, the trend of mobility was altered and the radiative efficiency fitted experimental values well.

A white organic light-emitting device (WOLED) based on a phosphorescent blue and green emitter combined with red fluorescent one doped in a single host is presented. In such a device, efficient phosphorescent sensitization (PS) was achieved from the green phosphorescent emitter to the red fluorescent one, which was directly observed from transient electroluminescence. An undoped region was inserted between the green and blue dopant region to stabilize the emission spectra. In this configuration, the main recombination zone was at the blue-emitting region, and the minor one was located at the green one near the undoped region. To avoid carrier trapping, the red fluorescent emitter with a reasonably high concentration (0.5%) was doped away from the minor recombination zone. That WOLED exhibited a longer operation lifetime than the phosphorescent blue/green device, because the PS provided a radiative efficient energy relaxation from the green phosphorescent emitter to the red fluorescent one.

This work demonstrated a-Si:H thin-film solar cells with backside TiO(2) / SiO(2) distributed Bragg reflectors (DBRs) for applications involving building-integrated photovoltaics (BIPVs). Selectively transparent solar cells are formed by adjusting the positions of the DBR stop bands to allow the transmission of certain parts of light through the solar cells. Measurement and simulation results indicate that the transmission of blue light (430 ~500 nm) with the combination of three DBR mirrors has the highest increase in conversion efficiency.

An efficient ITO-free top-illuminated organic photovoltaic (TOPV) based on small molecular planar heterojunction was achieved by spinning a buffer layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), on the Ag-AgOx anode. The PEDOT:PSS thin film separates the active layer far from the Ag anode to prevent metal quenching and redistributes the strong internal optical field toward dissociated interface. The thickness and morphology of this anodic buffer layer are the key factors in determining device performances. The uniform buffer layer contributes a large short-circuit current and open-circuit voltage, benefiting the final power conversion efficiency (PCE). The TOPV device with an optimal PEDOT:PSS thickness of about 30 nm on Ag-AgOx anode exhibits the maximum PCE of 1.49%. It appreciates a 1.37-fold enhancement in PCE over that of TOPV device without buffer layer.

Summary form only given. Characterization of third-order optical nonlinearity (/spl chi//sup (3)/) is essential in applications like optical switching and optical communication, etc. The existing methods, however, suffer from either the complexity of the experimental setup (such as four-wave mixing) or the low sensitivity (Z-scan). Recently, with femtosecond laser pulses, Wise et al. (1997-98) demonstrated a simple method to determine refractive, absorptive and Raman-induced /spl chi//sup (3)/, based on the spectrally-resolved two-beam coupling (SRTBC) method. The usage of their simple model is, however, limited to transform-limited laser pulses. We extend the SRTBC method to chirped pulses.

We have successfully fabricated a low-reflection organic light-emitting diode (LR-OLED) by replacing the highly reflective Al cathode of a conventional OLED with a Fabry–Pérot (FP) cavity cathode, which is simultaneously responsible for absorption, plasmonic absorption and destructive interference. The FP cavity cathode consisted of a front semi-transparent double thin metal layer (Al/Ag), an inserted organometallic black layer (BL) in the middle and a highly reflective Al mirror. The organometallic BL contained a high-mobility electron transport and broadband absorptive organic matrix, N,N′-bis(2,6-diisopropylphenyl)-1,7-bis(4-methoxy-phenyl)perylene-3,4,9,10-tetracarboxydiimide (MPPDI), and Ag-nanoparticle (NP) dopants which contributed not only to the plasmonic absorption but also to the metallic conductivity. By adjusting the thickness and Ag-NP concentration of the organometallic BL, one can optimize the destructive interference cavity effect. LR-OLEDs fabricated using the aforementioned characteristics of the Ag-NP yielded superior electrical performance and low reflection across almost the entire visible spectrum. With the exemption of surface reflection (air/glass ∼4%), a lowest reflection of 0% near 750 nm and an average reflection of 1.39% for the entire visible spectrum were obtained for a LR-OLED with a 65 nm organometallic BL (mixing ratio of MPPDI : Ag = 10 : 1). With the additional structural cavity cathode, the LR-OLEDs nonetheless exhibited similar electrical performances and continuous operational lifetimes to those of control devices with a traditional highly reflective Al cathode.

In this paper, we had quantitatively investigated the photoluminescence of organic emitter on a Si substrate with periodically corrugated metal thin film experimentally and theoretically. Due to the plasmonic coupling by the metal gratings, 4.3 times and 1.7 times enhancements in optical intensities were observed at specified and full viewing angles at certain wavelengths, respectively. Good agreement of angular-frequency versus in-plane wavevector (ω-k) curves between experiments and calculations were obtained when varying organic materials, metal materials, and grating pitches. Two different metal materials were used, which show slight shift in ω-k curves due to the high sensitivity of the surface plasmon to the relative permittivity.

In this paper, a highly conductive and strongly absorptive organic thin film by doping Ag into N,N′-bis (2,6-di-isopropylphenyl)-1,7-bis (4-methoxy-phenyl) perylene-3,4,9,10-tetracarboxydiimide (MPPDI) was demonstrated. Strong absorption resulted from the broadband absorption of MPPDI at visible range and plasmon-enhanced absorption around 420 nm of Ag nanoparticles. Ag dopants in MPPDI acted as quenchers, which resulted in a dramatic decrease in photoluminescence intensity of MPPDI. Besides, J-V characteristics of Ag:MPPDI thin film changed from trapped-charge-limited current to Ohmic conduction with increasing Ag concentrations. Conductivity of 1.15×10−6 Ω cm was achieved when MPPDI/Ag=5:1. This organic thin film has potential applications for low-reflectance organic light-emitting diode and organic photovoltaic device.

— A high-transmittance transflective device based on a hybrid structure consisting of a transparent organic light-emitting diode (OLED) stacked on top of a reflective liquid-crystal device (RLCD) was conceptually demonstrated. By placing the transparent OLED on top of a vertically aligned LCD operated under normally black mode, a transmittance as high as 75.7% was obtained due to the asymmetric emission characteristics of a transparent OLED. To further improve the performance in the transmissive mode, a polarizer-free LCD was used, which yielded an ultra-high transmittance (82.2% overall).