[1] Tang C W. VanSlyke S A. Organic electroluminescent diodes[J]. Applied Physics Letters, 1987, 51(12): 913-915.

[2] McCarthy M A, Liu B, Donoghue E P, et al. . Low-voltage, low-power, organic light-emitting transistors for active matrix displays[J]. Science, 2011, 332(6029): 570-573.

[3] Gu G, Forrest S R. Design of flat-panel displays based on organic light-emitting devices[J]. IEEE Journal of Selected Topics in Quantum Electronics, 1998, 4(1): 83-99.

[4] Shih C J, Lee C C, Yeh T H, et al. Versatile exciplex-forming co-host for improving efficiency and lifetime of fluorescent and phosphorescent organic light-emitting diodes[J]. ACS Applied Materials & Interfaces, 2018, 10(28): 24090-24098.

[5] Sotoyama W, Satoh T, Kinoshita M, et al. 39.3: material and device structure design of blue phosphorescent OLEDs for high efficiency and enhanced stability[J]. SID Symposium Digest of Technical Papers, 2010, 41(1): 556-559.

[6] Zhou L, Jiang Y L, Cui R Z, et al. Efficient red organic electroluminescent devices based on trivalent europium complex obtained by designing the device structure with stepwise energy levels[J]. Journal of Luminescence, 2016, 170(2): 692-696.

[7] Li Y N, Zhou L, Jiang Y L, et al. High performance pure blue organic fluorescent electroluminescent devices by utilizing a traditional electron transport material as the emitter[J]. Journal of Materials Chemistry C, 2017, 5(17): 4219-4225.

[8] Tao Y T, Yang C L, Qin J G. Organic host materials for phosphorescent organic light-emitting diodes[J]. Chemical Society Reviews, 2011, 40(5): 2943-2970.

[9] Sasabe H, Kido J. Multifunctional materials in high-performance OLEDs: challenges for solid-state lighting[J]. Chemistry of Materials, 2011, 23(3): 621-630.

[10] Kim B S, Lee J Y. Phosphine oxide type bipolar host material for high quantum efficiency in thermally activated delayed fluorescent device[J]. ACS Applied Materials & Interfaces, 2014, 6(11): 8396-8400.

[11] Cho Y J, Yook K S, Lee J Y. A universal host material for high external quantum efficiency close to 25% and long lifetime in green fluorescent and phosphorescent OLEDs[J]. Advanced Materials, 2014, 26(24): 4050-4055.

[12] Li W, Li J Y, Wang F, et al. Universal host materials for high-efficiency phosphorescent and delayed-fluorescence OLEDs[J]. ACS Applied Materials & Interfaces, 2015, 7(47): 26206-26216.

[13] Zhou X, Qin D S, Pfeiffer M, et al. High-efficiency electrophosphorescent organic light-emitting diodes with double light-emitting layers[J]. Applied Physics Letters, 2002, 81(21): 4070-4072.

[14] Li Y N, Zhou L, Jiang Y L, et al. Green organic light-emitting devices with external quantum efficiency up to nearly 30% based on an iridium complex with a tetraphenylimidodiphosphinate ligand[J]. RSC Advances, 2016, 6(68): 63200-63205.

[15] Yang Q, Hao Y Y, Wang Z G, et al. Double-emission-layer green phosphorescent OLED based on LiF-doped TPBi as electron transport layer for improving efficiency and operational lifetime[J]. Synthetic Metals, 2012, 162(3/4): 398-401.

[16] Lee S J, Koo J R, Lim D H, et al. Highly efficient and stable white organic light emitting diode base on double recombination zones of phosphorescent blue/orange emitters[J]. Journal of Nanoscience and Nanotechnology, 2011, 11(8): 7151-7154.

[17] Lee J, Lee J I, Chu H Y. Investigation of double emissive layer structures on phosphorescent blue organic light-emitting diodes[J]. Synthetic Metals, 2009, 159(14): 1460-1463.

[18] Lan Y H, Hsiao C H, Lee P Y, et al. Dopant effects in phosphorescent white organic light-emitting device with double-emitting layer[J]. Organic Electronics, 2011, 12(5): 756-765.