基于有机小分子和有机-无机杂化钙钛矿复合发光层的白光PeLED

White PeLED employing a mixed emission layer composed of a small organic molecule and an organic-inorganic hybrid perovskite

由于优越的光电特性和溶液加工特性,有机-无机杂化钙钛矿材料在发光显示领域展示出极大的应用前景.近两年,有机-无机杂化钙钛矿电致发光器件(Pe LED)得到了快速发展,电致发光效率已经达到了传统有机电致发光器件(OLED)的水平.由于白光是显示和照明领域的最主要光源,因此开发白光Pe LED具有重要的科学和商业价值.本文报道了以有机小分子1,3-bis(9-carbazolyl)benzene(m CP)和有机-无机杂化钙钛矿CH3NH3Pb Br3混合膜作为发光层的一种新型白光Pe LED.首先,通过一步旋涂工艺得到了均匀致密、覆盖度较高的m CP:CH3NH3Pb Br3晶体薄膜.然后以m CP:CH3NH3Pb Br3膜作为发光层的白光Pe LED(器件结构为ITO/PEDOT:PSS/m CP:CH3NH3Pb Br3/tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl(TPBI)/Li F/Al),器件的启亮电压为~3.2 V,最大亮度为~170 cd/m2,电致发光效率为~0.15 cd/A.当偏压为7 V时,Pe LED的CIE色坐标达到了(0.32,0.31),得到了理想的白光.该白光Pe LED基本达到了工业化的要求,同时也为进一步开发更高效、更稳定的白光Pe LED提供了参考思路.

Organic-inorganic hybrid perovskites are classes of direct-bandgap semiconductors that enjoy outstanding optoelectric properties and feasible solution processing. Besides being demonstrated as a new class of photovoltaic materials for next-generation （solar cell with efficiency〉20%）, the organic-inorganic hybrid perovskites are showing great potential in lightings and displays because of their high brightness and tunable color across the entire visible range. Since Chondroudis and Mitzi first reported the room-temperature electroluminescence from organic-inorganic hybrid perovskites, remarkable progresses have been made in organic-inorganic hybrid perovskite electroluminescent devices （PeLED）, including reducing the grain size of polycrystalline perovskite, improving the morphologies of perovskite film and bipolar charge injection into the emissive layer. Notably, electroluminescence （EL） efficiencies of organic-inorganic hybrid perovskites have been recently boosted to 42.9 cd/A by Cho et al. via a nanocrystal pinning method, getting close to the level of organic light-emitting diodes （OLED）. Despite these advantages and the potential described above, the studies were mostly concerned in ＂green＂ PeLED based on CHaNHaPbBr3 or CsPbBr3 and there are few reports on white PeLED. Because white light plays most important role in daily life＇s lightings and displays, the developments of white PeLED should have significant values in both scientific research and commercial applications. In this work, a white PeLED employing a mixed emission layer composed of a small organic molecule of 1,3-bis（9-carbazolyl） benzene （mCP） and an organic-inorganic hybrid perovskite of CH3NH3PbBr3 was newly reported. Thus, the merits of good processability of organic small molecules and the excellent charge transportation properties of organic-inorganic hybrid perovskites can be well combined. The white PeLED were fabricated as follows： firstly, uniform and dense mCP：CH3NH3PbBr3 crystal film was prepared through one-step spin-coating techniques, resulting in relatively higher film coverage than that of pure CH3NH3PbBr3 film. Secondly, white PeLED composed of such mCP： CHaNHaPbBr3 mixed film was fabricated with the structure of ITO/PEDOT： PSS/mCP： CHaNHaPbBr3/tri（1-phenyl- 1H-benzo[d]imidazol-2-yl）phenyl （TPBI）/LiF/A1 through thermal evaporation, where the ITO was functionalized as the anode, the PEDOT：PSS was used as the hole injection layer, mCP： CH3NHaPbBr3 was emissive layer, TPBI was employed as electron transporting layer and hole blocking layer, and LiF/AI was the electron injection layer/cathode. Under electrical excitation, EL spectra show that the emissions of white PeLED were composed of RGB lights, i.e., deep-blue light （peak around 380 nm） coming from mCP molecules, green light （peak around 520 nm） coming from CH3NH3PbBr3 perovskites, and deep-red light （peak around 780 nm） coming from exciplex between mCP molecules and CH3NH3PbBr3 perovskites. The turn-on voltage of white PeLED was ~3.2 V, the maximum luminance was -170 cd/m2, and the EL efficiency was -0.15 cd/A. Moreover, the recombination zone can be effectively broadened with increasing the driving voltage, which tunes the color of white PeLED. At a driving voltage of 7 V, we got white emission with CIE coordinated at （0.32, 0.31 ）, indicating the white light was ideal. The results indicate that our white PeLED has already met the basical requirements of industry, and may provide a route for more efficient and stable white PeLED in the future.