ZnO nanocrystals incorporating PEIE and a fluorene-based polyelectrolyte as electron transport layers for pure cesium-containing perovskite light-emitting devices

We demonstrate inverted perovskite light-emitting devices (PeLEDs) based on ZnO nanocrystals (NCs) and cesium lead bromide (CsPbBr3) film as the electron transport and emission layers, respectively. Polyethyleneimine ethoxylated (PEIE) and an ionic polyfluorene derivative containing trimethylammonium hexafluorophosphate groups (namely P2-PF6) were introduced between ZnO NCs and CsPbBr3 film. The introduction of the PEIE/P2-PF6 bilayer decreased the work function of ZnO NCs to achieve balanced charge injection into the emission layer. Furthermore, the bilayer also effectively improved CsPbBr3 coverage and morphology, thereby reducing current leakage in PeLEDs. The improved CsPbBr3 film showed better photoluminescence, owing to anti-quenching capability of the PEIE/P2-PF6 and prolonged carrier lifetime. PeLEDs with the structure ITO/ZnO NCs/ PEIE/P2-PF6/CsPbBr3 film/poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenyl amine) (TFB)/Au were fabricated and evaluated, employing TFB as the hole transport layer. The PeLED based on the PEIE/P2-PF6 showed a turn-on voltage of 2.8 V, a max luminance of 3,927 cd/m2 and max current efficiency of 0.2 cd/A that was significantly higher than those without PEIE/P2-PF6 bilayer.

本研究展示了基于氧化锌纳米晶（ZnO NCs）与溴化铯铅（CsPbBr3）薄膜分别作为电子传输层与发光层的倒置型钙钛矿发光器件（PeLEDs）。在氧化锌纳米晶与溴化铯铅薄膜之间，引入了乙氧基化聚乙烯亚胺（PEIE）以及一种带有六氟磷酸三甲基铵基团的离子型聚芴衍生物（命名为P2-PF6）。PEIE/P2-PF6双层结构的引入可降低氧化锌纳米晶的功函数，实现向发光层的电荷平衡注入。此外，该双层结构还可有效提升溴化铯铅薄膜的覆盖度与形貌质量，进而降低钙钛矿发光器件中的电流泄漏问题。得益于PEIE/P2-PF6的抗淬灭能力以及载流子寿命的延长，经优化的溴化铯铅薄膜展现出更优异的光致发光性能。本研究制备并表征了结构为氧化铟锡（ITO）/ZnO NCs/PEIE/P2-PF6/CsPbBr3薄膜/聚(9,9-二辛基芴-co-N-(4-丁基苯基)二苯胺)（TFB）/金（Au）的钙钛矿发光器件，并以TFB作为空穴传输层。搭载PEIE/P2-PF6双层结构的器件展现出2.8 V的启亮电压、3927 cd/m²的最大亮度以及0.2 cd/A的最大电流效率，各项性能均显著优于未引入该双层结构的对照器件。