Although organic light-emitting devices have been commercialized as flat panel displays since 1997, only singlet excitons were emitted. Full use of singlet and triplet excitons, electrophosphorescence, has attracted increasing attentions after the premier work made by Forrest, Thompson, and co-workers. In fact, red electrophosphorescent dye has already been used in sub-display of commercial mobile phones since 2003. Highly efficient green phosphorescent dye is now undergoing of commercialization. Very recently, blue phosphorescence approaching the theoretical efficiency has also been achieved, which may overcome the final obstacle against the commercialization of full color display and white light sources from phosphorescent materials. Combining light out-coupling structures with highly efficient phosphors (shown in the table-of-contents image), white emission with an efficiency matching that of fluorescent tubes (90 lm/W) has now been realized. It is possible to tune the color to the true white region by changing to a deep blue emitter and corresponding wide gap host and transporting material for the blue phosphor. In this article, recent progresses in red, green, blue, and white electrophosphorescent materials for OLEDs are reviewed, with special emphasis on blue electrophosphorescent materials.

Recently, lead‐free double perovskites have emerged as a promising environmentally friendly photovoltaic material for their intrinsic thermodynamic stability, appropriate bandgaps, small carrier effective masses, and low exciton binding energies. However, currently no solar cell based on these double perovskites has been reported, due to the challenge in film processing. Herein, a first lead‐free double perovskite planar heterojunction solar cell with a high quality Cs2AgBiBr6 film, fabricated by low‐pressure assisted solution processing under ambient conditions, is reported. The device presents a best power conversion efficiency of 1.44%. The preliminary efficiency and the high stability under ambient condition without encapsulation, together with the high film quality with simple processing, demonstrate promise for lead‐free perovskite solar cells.

High efficiency in organic light-emitting devices (OLEDs) is a crucial factor to promote the application of OLEDs in the next generation of flat panel displays. In an OLED, the generation of light is the consequence of the recombination of holes with electrons within the organic emitting material (EM) injected from the electrodes. Therefore, the efficiency of an OLED is composed of the recombination efficiency of holes with electrons and the photoluminescence quantum yield of the EM. Based on the conventional layered structure of an OLED, an emission extraction efficiency of 1/(2n 2 ) can be obtained (where n is the refractive index of the organic material, which is about 1.6 [1] ). In the case of a fluorescent emitter, 25% of internal quantum efficiency (IQE, which corresponds to $5% of an external quantum efficiency (EQE)) can be obtained from the 25% of singlet spin states. When a phosphorescent emitter is applied, the remainder 75% of triplet spin states can also emit light. Therefore, an IQE of 100% (which corresponds to $20% of EQE) can theoretically be obtained. [2] In fact, (87 AE 7)% of an IQE (which corresponds to about 19% of an EQE) was obtained in a green-light electrophosphorescent device using a phosphorescent dye, bis(2-phenylpyridinato)iridium(III) acetylacetonate [(ppy) 2 Ir (acac)], as the emitter.[3] Recently, a near theoretical limitation of green-light emission (over 20% of EQE) was obtained using fac tris(2-phenylpyridinato)iridium(III) [Ir(ppy) 3 ] as the phosphorescent emitter. [4] In the case of a blue-light electrophosphorescent device, although the EQE can be effectively improved up to 16% by using an exothermic host-guest energy transfer from a wideenergy-gap (E g ) host with high enough triplet energy (E T ) to confine the triplet excitons of the blue-light emitter iridium(III) bis [(4,6-(FIrpic), [5] there is still room for further improvement in efficiency. In comparison to the higher efficiency of green-light emission previously reported, [3,4] a further improvement in the efficiency of blue light is crucial to realize the full colorization of OLEDs. Blue light is not only one of the three primary colors, from which white light can be obtained, [6] but can also generate other low-energy emissions, such as green and red, by using a color-change medium. Kawamura et al. demonstrated that the photoluminescence quantum yield of FIrpic could reach nearly 100% when doped in the wide E g host of N,N 0 -dicarbazolyl-3,5-benzene (mCP).[7] Therefore, an effort should be made to improve the charge recombination efficiency by using efficient chargetransporting materials to maintain the charge balance in the devices. In general, the mobility of holes is much higher than that of electrons in organic semiconducting materials.[8] To further improve the efficiency, the development of efficient electrontransporting (ET) materials is still a major objective. Although some reports have been conducted towards this, for example, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), [9a,9b] aluminum(I...