Engineering carrier transport across organic heterojunctions by interface doping

Two common hole transporting materials, 4,4('),4(')-tris(N-3-methylphenyl-N-phenyl-amino) triphenylamine (MTDATA) and N,N-'-diphenyl-N,N-'-bis(1-naphthyl) (1,1(')-biphenyl)-4,4(')diamine (NPB), and a p-type dopant tetrafluorotetracyanoquinodimethane (F-4-TCNQ) were used to build various hole-only heterojunction devices. Both experimental results and theoretical modeling show that the current flow in such devices is limited by the heterojunction potential barrier or band offset at the MTDATA/NPB interface. It was found that the device current flow can be modulated to increase or decrease dramatically by introducing a 2 nm p-doped NPB:F-4-TCNQ or MTDATA:F-4-TCNQ interlayer, respectively. The observed phenomena were discussed using quasi-Fermi energy level realignment at the doped/undoped organic-organic interface. (c) 2007 American Institute of Physics.