Enhanced Emitting Dipole Orientation Based on Asymmetric Iridium(III) Complexes for Efficient Saturated-Blue Phosphorescent OLEDs

Kefei Shi; Chengcheng Wu; He Zhang; Kai-Ning Tong; Wei He; Wansi Li; Zhaoyun Jin; Sinyeong Jung; Siqi Li; Xin Wang; Shaolong Gong; Yuewei Zhang; Dongdong Zhang; Feiyu Kang; Yun Chi; Chuluo Yang; Guodan Wei

doi:10.1002/advs.202402349

Enhanced Emitting Dipole Orientation Based on Asymmetric Iridium(III) Complexes for Efficient Saturated-Blue Phosphorescent OLEDs

Adv Sci (Weinh). 2024 Oct;11(38):e2402349. doi: 10.1002/advs.202402349. Epub 2024 Aug 13.

Authors

Kefei Shi^{1

2}, Chengcheng Wu^{1

2}, He Zhang³, Kai-Ning Tong², Wei He², Wansi Li¹, Zhaoyun Jin², Sinyeong Jung^{1

2}, Siqi Li², Xin Wang², Shaolong Gong³, Yuewei Zhang⁴, Dongdong Zhang⁵, Feiyu Kang², Yun Chi⁶, Chuluo Yang⁷, Guodan Wei^{1

2}

Affiliations

¹ Tsinghua-Berkeley Shenzhen Institute (TBSI), Tsinghua University, Shenzhen, 518055, China.
² Institute of Materials Research, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen, 518055, China.
³ Hubei Key Lab on Organic and Polymeric Optoelectronic Materials, Department of Chemistry, Wuhan University, Wuhan, 430072, China.
⁴ Laboratory of Flexible Electronics Technology, Tsinghua University, Beijing, China.
⁵ Key Laboratory of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, China.
⁶ Department of Materials Science and Engineering, Department of Chemistry and Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Hong Kong SAR, 999077, China.
⁷ Shenzhen Key Laboratory of New Information Display and Storage Materials, College of Materials Science and Engineering, Shenzhen University, Shenzhen, 518060, China.

Abstract

Three novel asymmetric Ir(III) complexes have been rationally designed to optimize their emitting dipole orientations (EDO) and enhance light outcoupling in blue phosphorescent organic light-emitting diodes (OLEDs), thereby boosting their external quantum efficiency (EQE). Bulky electron-donating groups (EDGs), namely: carbazole (Cz), di-tert-butyl carbazole (tBuCz), and phenoxazine (Pxz) are incorporated into the tridentate dicarbene pincer chelate to induce high degree of packing anisotropy, simultaneously enhancing their photophysical properties. Angle-dependent photoluminescence (ADPL) measurements indicate increased horizontal transition dipole ratios of 0.89 and 0.90 for the Ir(III) complexes Cz-dfppy-CN and tBuCz-dfppy-CN, respectively. Analysis of the single crystal structure and density functional theory (DFT) calculation results revealed an inherent correlation between molecular aspect ratio and EDO. Utilizing the newly obtained emitters, the blue OLED devices demonstrated exceptional performance, achieving a maximum EQE of 30.7% at a Commission International de l'Eclairage (CIE) coordinate of (0.140, 0.148). Optical transfer matrix-based simulations confirmed a maximum outcoupling efficiency of 35% due to improved EDO. Finally, the tandem OLED and hyper-OLED devices exhibited a maximum EQE of 44.2% and 31.6%, respectively, together with good device stability. This rational molecular design provides straightforward guidelines to reach highly efficient and stable saturated blue emission.

Keywords: OLED; iridium; molecular orientation; outcoupling; phosphorescence.

Abstract

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