A Yellow-Emitting Homoleptic Iridium(III) Complex Constructed from a Multifunctional Spiro Ligand for Highly Efficient Phosphorescent Organic Light-Emitting Diodes

Bao-Yi Ren; Run-Da Guo; Dao-Kun Zhong; Chang-Jin Ou; Gang Xiong; Xiang-Hua Zhao; Ya-Guang Sun; Matthew Jurow; Jun Kang; Yi Zhao; Sheng-Biao Li; Li-Xin You; Lin-Wang Wang; Yi Liu; Wei Huang

doi:10.1021/acs.inorgchem.7b01034

A Yellow-Emitting Homoleptic Iridium(III) Complex Constructed from a Multifunctional Spiro Ligand for Highly Efficient Phosphorescent Organic Light-Emitting Diodes

Inorg Chem. 2017 Jul 17;56(14):8397-8407. doi: 10.1021/acs.inorgchem.7b01034. Epub 2017 Jun 28.

Authors

Bao-Yi Ren^{1

2}, Run-Da Guo³, Dao-Kun Zhong¹, Chang-Jin Ou², Gang Xiong¹, Xiang-Hua Zhao², Ya-Guang Sun¹, Matthew Jurow, Jun Kang, Yi Zhao³, Sheng-Biao Li⁴, Li-Xin You¹, Lin-Wang Wang, Yi Liu, Wei Huang²

Affiliations

¹ Key Laboratory of Inorganic Molecule-Based Chemistry of Liaoning Province, College of Applied Chemistry, Shenyang University of Chemical Technology , Shenyang 110142, P. R. China.
² Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing University of Posts & Telecommunications , 9 Wenyuan Road, Nanjing 210023, P. R. China.
³ State Key Laboratory on Integrated Optoelectronics, College of Electronics Science and Engineering, Jilin University , Changchun 130012, P. R. China.
⁴ College of Chemistry, Central China Normal University , Wuhan 430070, P. R. China.

PMID: 28657296
DOI: 10.1021/acs.inorgchem.7b01034

Abstract

To suppress concentration quenching and to improve charge-carrier injection/transport in the emission layer (EML) of phosphorescent organic light-emitting diodes (PhOLEDs), a facial homoleptic iridium(III) complex emitter with amorphous characteristics was designed and prepared in one step from a multifunctional spiro ligand containing spiro[fluorene-9,9'-xanthene] (SFX) unit. Single-crystal X-ray analysis of the resulting fac-Ir(SFXpy)₃ complex revealed an enlarged Ir···Ir distance and negligible intermolecular π-π interactions between the spiro ligands. The emitter exhibits yellow emission and almost equal energy levels compared to the commercial phosphor iridium(III) bis(4-phenylthieno[3,2-c]pyridinato-N,C²')acetylacetonate (PO-01). Dry-processed devices using a common host, 4,4'-bis(N-carbazolyl)-1,1'-biphenyl, and the fac-Ir(SFXpy)₃ emitter at a doping concentration of 15 wt % exhibited a peak performance of 46.2 cd A^-1, 36.3 lm W^-1, and 12.1% for the current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE), respectively. Compared to control devices using PO-01 as the dopant, the fac-Ir(SFXpy)₃-based devices remained superior in the doping range between 8 and 15 wt %. The current densities went up with increasing doping concentration at the same driving voltage, while the roll-offs remain relatively low even at high doping levels. The superior performance of the new emitter-based devices was ascribed to key roles of the spiro ligand for suppressing aggregation and assisting charge-carrier injection/transport. Benefiting from the amorphous stability of the emitter, the wet-processed device also exhibited respectful CE, PE, and EQE of 32.2 cd A^-1, 22.1 lm W^-1, and 11.3%, respectively, while the EQE roll-off was as low as 1.7% at the luminance of 1000 cd m^-2. The three-dimensional geometry and binary-conjugation features render SFX the ideal multifunctional module for suppressing concentration quenching, facilitating charge-carrier injection/transport, and improving the amorphous stability of iridium(III)-based phosphorescent emitters.