Fig. 3: Change of energy level and morphology.

a Illustration for the electron transfer between PolyTPD and BCF. b Flat energy level (band) diagrams for the explanation of electron transfer-mediated doping mechanism between PolyTPD and BCF. c Phase-mode AFM images (2 μm × 2 μm) for the PolyTPD:BCF films (48 h) according to the doping time. d Change of root-mean-square roughness (Rg) and phase angle (AP) according to the doping time for the PolyTPD:BCF films (48 h).