Improved green thermal activated delayed fluorescence OLEDs based on thermally evaporated distributed Bragg reflector (DBR) of MgF2/ZnS

Yanqiong Zheng; Juncong Chen; Weiguang Li; Chao Wang; Junbiao Peng; Bin Wei; Xifeng Li

doi:10.1088/1361-6528/ac1b51

Improved green thermal activated delayed fluorescence OLEDs based on thermally evaporated distributed Bragg reflector (DBR) of MgF₂/ZnS

Nanotechnology. 2021 Aug 20;32(45). doi: 10.1088/1361-6528/ac1b51.

Authors

Yanqiong Zheng¹, Juncong Chen^{1

2}, Weiguang Li^{1

2}, Chao Wang^{1

2}, Junbiao Peng³, Bin Wei¹, Xifeng Li¹

Affiliations

¹ Key Laboratory of Advanced Display and System Applications of Ministry of Education, School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200072, People's Republic of China.
² School of Materials Science and Engineering, Shanghai University, Shanghai 200072, People's Republic of China.
³ State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, People's Republic of China.

PMID: 34415853
DOI: 10.1088/1361-6528/ac1b51

Abstract

Unlike the traditional fabrication of distributed Bragg reflector (DBR) structure via atomic layer deposition or spin-coating, here the 1-6 pairs of magnesium fluoride (MgF₂)/zinc sulfide (ZnS) alternative dielectric layers were grown via thermal evaporation. The absorption, transmission, reflection, and photoluminescence (PL) spectra were evaluated. 5 pair MgF₂/ZnS denotes the largest reflectance (88.5% at 535 nm) together with a stopband at 450-650 nm among the 1- 6 pair dielectric layers, exhibiting the potential for using as DBR. Relative to the bare 4,4'-bis(carbazol-9-yl)biphenyl(CBP):(4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl) isophthalonitrile (4CzIPN) film, the PL intensity of CBP:4CzIPN/5 pair MgF₂/ZnS DBR is enhanced and splitted into two peaks. The 5 pair alternative dielectric film presents more uniform aggregation over 4 pair MgF₂/ZnS. The cross-sectional scanning electron microscopic image denotes explicit layering for the MgF₂and ZnS. The organic light-emitting diode (OLED) incorporating 5 pair MgF₂/ZnS DBR layers illustrates significantly improved electroluminescent (EL) performance due to the photons concentrated in the direction perpendicular to the DBR. The slightly narrowed EL spectrum is originated from the microcavity effect between the two Al electrodes. Here we develop a universal method for the DBR fabrication suitable to most of OLEDs.

Keywords: MgF2/ZnS; distributed Bragg reflector; green delayed fluorescence OLED; thermal evaporation.