Luminescence efficiency

A sample holder, including optics for focusing the incident light and collecting the luminescence. Efficient light collection is important, and the sample holder may need to allow for a cryostat, pressure cell, magnet, or electrical contacts. 

The composition of the copolymer determines its electroluminescence efficiency. Optimal efficiency (0.3%) was achieved in system 34 when the feed ratio of monomer 4 to monomer 34 was 9 1. This represents a 30-fold improvement in luminescence efficiency relative to PPV in the same device configuration (AlALOj/polymer/Al) 58, 62. Copolymer 33 has found uses as waveguides and... 

In electroluminescence devices (LEDs) ionized traps form space charges, which govern the charge carrier injection from metal electrodes into the active material [21]. The same states that trap charge carriers may also act as a recombination center for the non-radiative decay of excitons. Therefore, the luminescence efficiency as well as charge earner transport in LEDs are influenced by traps. Both factors determine the quantum efficiency of LEDs. 

Fig. 9. Temperatures dependence of the luminescence efficiency of the system Cai-jPbiWO for three values of X (modified from JA Groenink, thesis, Utrecht, 1979)...

EL from tetraalkoxy-substituted PPV 20, synthesized by Gilch polymerization, was recently reported [84], A multilayer device ITO/PEDOT/20/PBD/LiF/Al with PBD as an ETL emits green-yellow light with a luminescent efficiency of 0.121m/W, a maximum brightness of 8200 cd/m2, and a turn-on voltage of 5 V. 

Ma and coworkers [154] synthesized a bipolar luminescent PPV-based polymer 111, which contained both donor triarylamine and acceptor oxadiazole moieties in the backbone. A device fabricated with this polymer (ITO/PEDOT/111/CsF/Al) showed a maximum brightness of 3600 cd/m2 and a maximum luminescent efficiency of 0.65 cd/A (< el = 0.3%), about 15 times brighter and more efficient than the device of the same configuration with a nonoxadiazole polymer 112. 

A certain balance should be kept in distortion of the thiophene planarity as a way to prevent the formation of interchain aggregates. Introducing two substituents at positions 3 and 4 of PT allows a shift of the emission through the entire visible range and prevents interchain interactions (resulting in a smaller decrease of the quantum yield in the solid state compared to solution). Highly crowded disubstituted PTs 418 421 show very low luminescence efficiency already in solution (Table 2.5) due to substantial distortion of the backbone [107,498],... 

Spiro-shaped HTMs have been studied extensively (Scheme 3.16) [88,89], The introduction of a spiro center improves the thermal stability of the amorphous state without significantly changing charge-transport properties. Compared with using NPD, TPD HTMs, using 43 in ITO/HTM/Alq3/LiF/Al devices showed very high luminescent efficiency [90]. 

Kodak recently applied for a patent on a series of green dopants based on the [1,2,3-cd]perylene skeleton (140) [197,198,199]. They claim using the [1,2,3- /]pcrylene dopant improves the luminescent efficiency (7.4 cd/A) and stability (lifetime >2200 h at 70°C)... 

Ueno studied a series of different triaryl- or tetraaryl-benzene host materials and found that using triarylbenzene (TPB3, 190) (Scheme 3.58) as a host material with a DSA-amine (Ide 102, 191) doped OLED showed a peak luminance of 142,000 cd/m2 at 12 V. This device also showed a luminescent efficiency of 6.0 lm/W at 5 V and 820 cd/m2 and an external efficiency of 2.4%. The lifetime of the device is also better than that of a device with DPVBI as the host. 

Several groups have studied naphthalene substituted anthracene derivatives as hosts or emitter materials in blue OLEDs (121, 202-205) (Scheme 3.63). The Kodak group used ADN as a host and TBP as a dopant in ITO/CuPc/NPD/ADN TBP/Alq3/Mg Ag [241]. They achieved a narrow vibronic emission centered at 465 nm with CIE (0.154, 0.232) and a luminescent efficiency as high as 3.5 cd/A. In comparison, the undoped device shows a broad and featureless bluish-green emission centered at 460 nm with CIE (0.197, 0.257) and an EL efficiency below 2.0 cd/A. The operational lifetimes of the doped device and the undoped device were 4000 and 2000 h at an initial luminance of 636 cd/m2 and 384 cd/m2, respectively. 

Spiro-FPAl/TPBI/Bphen Cs/Al. A very low operating voltage of 3.4 V at luminance of 1000 cd/m2 was obtained, which is the lowest value reported for either small-molecule or polymer blue electroluminescent devices. Pure blue color with CIE coordinates (0.14, 0.14) have been measured with very high current (4.5 cd/A) and quantum efficiencies (3.0% at 100 cd/m2 at 3.15 V) [245]. In another paper, Spiro-FPA2 (126) was used as a host material with an OLED device structure of ITO/CuPc/NPD/spiro-FPA2 l%TBP/Alq3/LiF that produces a high luminescent efficiency of 4.9 cd/A [246]. 

Beryllium chelates such as bis[2-(2-hydroxyphenyl)-pyridine]beryllium (Beq2, 86) (Scheme 3.74) emit pure blue light with an emission peak centered at 465 nm [269]. ITO/NPD/Bepp2/LiF/Al exhibited a maximum luminance of 15,000 cd/m2 and amaximum luminescent efficiency of 3.43 lm/W (3.8 cd/A). The emission color may have contributions from both NPD and Bepp2 as stated by the authors. 

Very recently, UDC claimed that they have successfully achieved a luminescent efficiency of 22 cd/A for a sky blue PHOLED with CIE (0.16,0.37) with over 15,000 h operating lifetime at 200 cd/m2 [317], The possible chemical structure of this sky blue emitter probably involves replacing the phenyl ring of phenylpyrazolyl with an extended fluorenyl unit, which has effective emission at room temperature, as presented at a recent ACS meeting by Forrest [318]. 

In their follow-up paper, they also demonstrated 100% efficient energy transfer of both singlet and triplet excited states. The device exhibits peak external efficiency and power efficiency of 25 cd/A and 17 lm/W at 0.01 mA/cm2, respectively [343]. Liu demonstrated a high-efficiency red OLED employing DCJTB as a fluorescent dye doped in TPBI with a green phosphorescent Ir(ppy)3 as a sensitizer. A maximum brightness and luminescent efficiency of... 

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