ABSTRACT
Organic Interfaces ...................................................................................... 185 6.4 Experimental Techniques ......................................................................... 187 6.5 Electronegativity Model for Barrier Formation at Metal/Organic
Interfaces ..................................................................................................... 189 6.5.1 Work Function versus Electronegativity .................................... 189 6.5.2 Extension of the Electronegativity Concept ............................... 194
6.6 O/O Heterojunctions ................................................................................. 195 6.6.1 Substrate Effect on Alq3/CuPc Interface ..................................... 196 6.6.2 Energy-Level Alignment at Different O/O
Heterojunctions .............................................................................. 199 6.7 Implications ................................................................................................ 203
6.7.1 Ambipolar Organic Field-Effect Transistor ................................ 203 6.7.2 Stacked Organic Light-Emitting Diode ...................................... 204
6.8 Conclusions ................................................................................................. 207 Acknowledgment ................................................................................................ 208 References ............................................................................................................. 208
An epoch of using organic materials for electrical, electronic, and optoelectronic applications has been going on since 1977, when Chiang et al. [1] discovered a tremendous increase of 11 orders of magnitude in electrical conductivity of polymer when halogen was introduced into polyacetylene. A new nomenclature of “organic semiconductors” was therefore coined
specifi cally for this new class of conducting materials. In the last 20 years, organic semiconductors have graduated rapidly from a topic of research interest to a material with a wide range of applications, which include polymer light-emitting diodes (PLEDs) [2,3], small-molecule-based organic light-emitting diodes (OLEDs) [4-7], organic lasers [8,9], organic transistors [10-12], solar cells [13-15], organic memory [16,17], etc.
