Abstract
Though optically pumped lasing has been realized for years, electrically pumped lasing has not yet been achieved in organic semiconductor devices. In order to make a better understanding of the laser mechanisms of the organic materials, we prepared organic thin films consisting of three efficient laser dyes of a blue emitter, 4″,4″′-N,N-diphenylamine-4,4′-diphenyl-1,1′-binaphthyl (BN), a green emitter, 1,4-bis[2-[4-[N,N-di(p-tolyl)amino] phenyl]vinyl]benzene (DSB), and a red emitter, 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidy-l-9-enyl)-4H-pyran (DCJTB) with different doping concentrations for the first time to investigate the cascade energy transfer process. The energy transfer schemes in the co-doped thin films in photoluminescence and electroluminescence have been investigated. The results indicated that the DSB molecules acted as a bridge to deliver energy more effectively from the host (BN) to the guest (DCJTB). Meanwhile, the maximum current efficiency (CE) and power efficiency (PE) of the organic light-emitting devices (OLEDs) with the emitting layer of lower doping concentration were 13.5 cd/A and 14.1 lm/W, respectively.
Highlights
The realization of electrically pumped lasing is still considered as a significant challenging research subject in the field of organic semiconductor devices, though various approaches have been attempted [1,2,3]
BN has a strong emission in the deep blue (436 nm) region, followed by a shoulder at 510 nm, while the absorption peak of DCJTB is fitly at 468 nm, and the spectra overlap ratio is 86.05%, providing possibilities for efficient energy transfer
We discover that the overlap between the PL spectrum of BN and the absorption spectrum of DSB is large and the superposition between the PL spectrum of DSB and the absorption spectrum of DCJTB is enormous as well, with the spectra overlap ratios of 61.68% and 91.92%, respectively
Summary
The realization of electrically pumped lasing is still considered as a significant challenging research subject in the field of organic semiconductor devices, though various approaches have been attempted [1,2,3]. At present, stimulated emission behavior, including amplified spontaneous emission (ASE), is observed in organic lasing dyes [4,5,6,7,8,9,10], yet the stimulated emission is eventually hampered by the low-efficiency energy transfer mechanism and concomitant singlet-triplet annihilation, which prohibits a sustained population inversion [11,12]. The low efficiency problem caused by annihilation can be resolved by adding an auxiliary film-forming polymer to dilute the laser dye mixed solutions [13,14]. We demonstrated a cascade host-guest energy system by mixing three high-efficiency organic laser dyes (4′′,4′′′-N,N-diphenylamine-4,4′-diphenyl-1,1′-binaphthyl (BN), 1,4-bis[2-[4-[N,N-di(p-tolyl)amino] phenyl]vinyl]benzene (DSB), and 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7tetramethyljulolidy-l-9-enyl)-4H-pyran (DCJTB)) in an organic polymer film. We inserted the hybrid thin film into organic light-emitting devices (OLEDs) serving
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