Fig. 3

Electroluminescence (EL) in cavity-free and cavity-based OLEDs. a The device structure of cavity-free F8BT OLED. b Broad EL spectrum for cavity-free OLED. c Negligible magneto-EL at different injection currents for broad EL in cavity-free OLED. d Narrow EL spectra for cavity-based OLEDs with different Q-factors. e Magneto-EL for cavity-based OLEDs with different Q-factors at constant injection current (20 mA cm−2)