Synergy of solid-state solvation and microcavity effects for efficient blue OLEDs based on green thermally activated delayed fluorescence emitter

Emission spectral shift has a significant influence on the color purity of organic light-emitting diodes (OLEDs) for the applications in full-color displays and solid-state lighting. However, the controllable shift of the emission spectra from one color to another provides a promising method to solve the problem in high-performance blue emitters. Here, we demonstrate the tunable emission colors from green to blue with the use of a green emitter of 2,4,5,6-tetrakis(carbazol-9-yl)-1,3-dicyanobenzene (4CzIPN) with different doping concentrations. Upon an optimal 4CzIPN doping concentration of 1 wt%, the OLED achieves a blue emission at 488 nm with the maximum current efficiency of 41.69 cd/A, the maximum power efficiency of 43.66 lm/W, and Commission International de I'Eclairage (CIE) coordinates of (0.19, 0.39). By investigating the factors of the polarity of the host materials and the use of electron-transport layers, it has been clarified that the electroluminescence spectral shift arises from the synergistical effects of solid-state solvation and microcavity. These findings pave the way for the development of high-efficiency blue OLEDs without blue materials.