Herein, we report flexible deep‐red quantum‐dot light‐emitting diodes on ITO/PEN substrates with narrow bandwidth, long shelf‐life, external quantum efficiency up to 8.3%, and high brightness of 42214 cd/m 2 (8 mm 2 pixel at 5.8 V) equivalent to 19.6 mW/cm 2 .sr, which are ideal light sources for photomedicine, i.e. photodynamic therapy and photobiomodulation.