西安交大科研人員製備具有高穩定性鈣鈦礦藍光電致發光二極體
Highly StablePerovskiteBlue-emitting Electroluminescent Diodes Made by XJTU Researchers
藍光材料及其發光二極體在照明和顯示中起著至關重要的作用。近年來，得益於其低成本、光譜易調諧、高載流子遷移率及高螢光量子效率等優勢，基於鈣鈦礦材料的發光二極體（PeLED）由於高發光效率成為國際研究熱點。目前，綠光、紅光及紅外光波段PeLED器件的外量子效率（EQE）均超過20%。相比來說，藍光PeLED研究卻進展緩慢，成果寥寥。作為白光三原色之一，與綠光和紅光相比，藍光二極體已被證明是最具挑戰性的。藍光PeLED器件性能低下的主要原因是藍光鈣鈦礦材料成膜質量差（薄膜不連續、輻射效率低、材料不穩定等）以及器件結構設計不合理（能級不匹配、載流子有效注入差及漏電流大）。目前為止，大量工作通過離子摻雜、界面工程及維度調控等方式實現了藍光PeLED器件性能的提升。然而，兼具高效且穩定的藍光PeLED器件的實現仍具挑戰。
Blue-lightmaterials and their light emitting diodes（LEDs）play a vitalrole in lighting and displays. In recent years, LEDs based on organomentalhalide perovskite (PeLED) has become an international research hotspot due toits low cost, tunable emittingwavelength with high photoluminescence quantum yield (PLQY) and good mobility. Inspiringly,green, red and near-infrared PeLEDs with external quantum efficiency (EQE) over20% have been reported recently. In contrast, the blue-emitting PeLED research hasshown limited advancement. Blue is one of the three primary colors of whitelight and the blue-light diode has proven to be the most challenging comparedwith its green or red counterparts. The main reasons for the poor performanceof blue light PeLED devices are poor film quality of the blue-emittingperovskite materials (film discontinuity, lowradiation efficiency, material instability, etc.) and unscientific devicestructure (energy mismatch, poor carrier injection and high leakage current).So far, by means of ion doping, interface engineering and dimension control,performance of blue-emitting PeLED device has been improved by unremittingefforts. Nevertheless, developing efficient and stable blue PeLED devices isstill challenging.針對以上藍光PeLED器件中存在的問題，西安交大吳朝新教授團隊採用調製「雞尾酒」的方式，在無機鈣鈦礦CsPb(Cl/Br)3中引入多重陽離子Rb/FA/PEA/K，協同作用，各司其職，解決藍光鈣鈦礦材料固有缺點（輻射複合效率低及穩定性差等）的同時，通過離子誘導結晶改善成膜質量，製備出兼具高螢光量子效率（~17.1%）、高平整度及高穩定性的多重陽離子鈣鈦礦(Cs/Rb/FA/PEA/K)Pb(Cl/Br)3薄膜；結合課題組提出的「絕緣層-鈣鈦礦-絕緣層」結構，即將鈣鈦礦薄膜置於兩層超薄絕緣層LiF之間，通過載流子隧穿效應，誘導載流子進入鈣鈦礦晶體內實現有效輻射複合，該結構能夠有效減少針孔引起的漏電流，抑制激子淬滅。最終，基於多重陽離子鈣鈦礦薄膜的藍光PeLED器件在電致發光波長484 nm處實現了最大發光亮度4015 cd/m2，最大EQE為2.01%的出色性能。最為重要的是，該器件表現出優異的工作穩定性，其連續工作狀態下的半衰壽命超過300 min。
In response to problemswith blue PeLED devices, the team led by Professor Wu Chaoxin from XJTU, via「cocktail」 strategy, introduced multiple cations Rb/FA/PEA/K into inorganicperovskite CsPb (Cl/Br)3. While multiple cations work incoordination to solve the inherent defects of blue light perovskite materials(such as low radiation recombination efficiency and poor stability etc.), italso develops the multiple-cations perovskite (Cs/Rb/FA/PEA/K)Pb(Cl/Br)3film with high fluorescence quantum efficiency（~17.1%）, highsmoothness and high stability by ion-induced crystallization to improve thequality of the film. Combined with 「insulating -perovskite-insulating」 (IPI) structureproposed by the research group, the perovskite film is placed between twoultra-thin insulator layers LiF, which are used to induce the charge injection intoperovskite crystals due to the tunneling effect. The structure proves effectivein blocking leakage currents caused by pinhole and avoiding exciton quenching. Finally,the blue PeLED device based on the multiple-cations perovskite film exhibits amaximum luminance of 4015 cd/m2 at 484 nm ofelectroluminescent wavelength., EQE of 2.01%. Most importantly, the deviceshows half-life stability over 300 minutes under continuous operation.這項工作表明多重陽離子調控策略為新型發光材料的設計開闢了新的途徑。同時，多重陽離子調控與「絕緣層—鈣鈦礦—絕緣層」結構的強強聯合，為未來設計兼具高效且高穩定的藍光PeLED器件提供了一個具有參考價值的新策略。
The research showsthat multiple-cations control strategy blazes a trail for the design of newluminescent materials. Meanwhile, the combination of multiple-cations controlwith the structure of IPI provides an original strategy with reference valuefor future design of high-efficiency and highly stable blue PeLED devices.該項研究工作近期發表於國際期刊《美國化學會能源快報》（ACS Energy Letters，影響因子16.331）。第一作者為課題組專職科研博士後袁方博士，吳朝新教授為唯一通訊作者，西安交通大學為第一作者單位和唯一通訊作者單位。該工作得到自然科學基金委項目、博士後面上項目、中央高校基本業務費等項目的支持。
The study hasrecently been published in an international journal the American ChemicalSociety Energy Letters (ACS Energy Letters, impactfactor 16.331). The first author is Dr. Yuan Fang, a full-time postdoctoralresearcher of the research group. Professor Wu Chaoxin is the onlycorresponding author and XJTU the affiliation of the first and the only correspondingauthors. The research project has been funded by the Nature Science FoundationCommittee (NSFC),China Postdoctoral Science Foundation,and Fundamental Research Funds for the Central Universities and others.吳朝新教授團隊長期研究新型功能材料的「光—電」與「電—光」物理機制及其器件應用如太陽能電池與發光二極體，近期有多項重要成果發表於國際頂級期刊：Joule，Advanced Materials, Advanced Functional Materials, Angewandte ChemieInternational Edition, ACS Energy Letters, Nano Energy等，更多研究內容可參見吳朝新教授主頁：http://zhaoxinwu.gr.xjtu.edu.cn。
Professor WuChaoxin’s team has longdedicated to the research of 「light-electricity」 and 「electricity-light」 physicalmechanism of new functional materials and its application in making devices,such as solar cell and LED. Recently, multiple important outcomes have beenpublished in top international journals: Joule, Advanced Materials, AdvancedFunctional Materials, Angewandte Chemie International Edition, ACS EnergyLetters, Nano Energy, etc. For more information, please visit ProfessorWu’s homepage:http://zhaoxinwu.gr.xjtu.edu.cn.