Wavelength-Turnable Organic Microring Laser Arrays from Thermally Activated Delayed Fluorescent Emitters

Abstract

Organic solid-state lasers (OSSLs) have been paid great attention due to their ease-of-fabrication, low cost and tailor-made molecular tunability. Optical gain materials of OSSLs are currently focused on fluorescent materials, which can bring only 25% exciton utilization for future current-injection OSSLs due to spin statics under electrical excitation. While thermally active delayed fluorescent (TADF) materials can obtain a theoretical 100% internal quantum efficiency by harvesting triplet excitons. However, OSSLs based on TADF materials remain largely unexplored yet. Here, we report the first TADF-based OSSL from whispering-gallery mode microring resonator arrays fabricated by a confined solution-growth method. The newly designed TADF emitter of carbozyl borondifluoride curcuminoid derivative, namely, CAZ-A, when doped into a host matrix of 4,4′-bis(N-carbazolyl)-1,10-biphenyl (CBP), reaches the highest gain-coefficient of 640 cm–1 at 4 wt %. These MRs with well-controlled sizes and uniform geometries constitute a high quality (cavity quality factor Q ∼ 1300) built-in WGM resonators and exhibit outstanding multimode laser behaviors. By varying TADF molecule doping concentration, the laser wavelength can be continuously tuned in the red spectral range from 650 to 725 nm. As CBP is usually used as the host material for active layers in OLEDs, we believe that CAZ-A/CBP doping material is good candidate for future electrically driven OSSLs.