Green Phosphorescent Dendrimer for Light-Emitting Diodes

Abstract

Highly efficient organic LEDs made by solution processing are reported. It is shown that the dendritic architecture (see Figure) can be used to solubilize luminescent chromophores and form uniform films of blends. The simple device structures containing a light‐emitting chromophore are amongst the most efficient solution‐processed devices reported. Thanks to this technique, the inkjet printing of phosphorescent materials becomes feasible.

Highly efficient single-layer dendrimer light-emitting diodes with balanced charge transport

“…11 We have found that the charge balance can be improved further at some expense of complexity by introducing an electron transporting/hole blocking layer to give a highly efficient bilayer device. 15 Even simpler device structures are desirable and, in this letter, we demonstrate device efficiency enhancement in a single-layer OLED structure. This is achieved by means of blending the components used in two-layer devices, thereby overcoming the limitations of poor charge injection and balance that are usually encountered in simple single-layer devices, and so giving major improvements in device performance, especially in terms of power efficiency.…”

Singlet energy transfer and singlet-singlet annihilation in light-emitting blends of organic semiconductors

“…7,8 The results show that IrG1 dendrimers can form uniform blends with CBP without any significant phase separation. We also report a study of singlet-singlet exciton annihilation in CBP films and discuss the implications for LEDs and lasers.…”

“…11,[15][16][17][18][19][20] A particularly widely used host for organic LEDs is the organic semiconductor 4 , 4Ј-bis͑N-carbazolyl͒biphenyl ͑CBP͒. [2][3][4][5][6][7][8][9] CBP is also of current interest as a host for laser gain media, with the potential for low threshold or even electrical pumping. 11,12 Given the widespread use of guest-host systems it is important to understand the energy transfer process from host to guest and the role of exciton-exciton annihilation in the host material.…”

Simple color tuning of phosphorescent dendrimer light emitting diodes

“…13,14 The HOMO levels of Ir-G1 and Ir͑ppy͒ 2 btp are 0.3 eV above those of CBP, implying that holes are readily trapped on both. 6,14 Figure 4 also suggests that electrons will be trapped on the dendrimers. Hence excitons are expected to form directly on the dendrimers, and this is supported by the absence of CBP emission.…”

“…We have therefore pursued the development of solution-processible electrophosphorescent dendrimers based on iridium ͑III͒ complexes. [5][6][7] Light-emitting dendrimers consist of a core, dendrons, and surface groups. They have shown great promise, with efficiencies of 55 cd/ A ͑40 lm/ W͒ at 4.5 V and 400 cd/ m 2 reported for two layer green emitting OLEDs 6 while in single layer devices a maximum power efficiency of 12.8 lm/ W at 8.1 V and 550 cd/ m 2 has been observed for the same dendrimer.…”