High hole mobility in the molecularly orderd oligosilanes

A single-dispersed oligosilane with a mesophase (smectic B) was utilized for fabricating molecularly ordered films. Their carrier transport properties were examined by the time-of-flight (TOF) transient photocurrent technique. In polycrystalline films of permethyldecasilane, molecular orientation almost parallel to bias electric field and a multi-layered structure were found, possessing large domain size (> 20 μ m). This unique molecular order resulted in non-dispersive TOF photocurrent with a clear plateau, whose hole mobility exceeded 1×10 −3 cm 2 /V s at 293 K, 1×10 5 V/cm. The high carrier mobility with small distribution can be ascribed to their well-ordered hopping sites. The unprecedented structure together with possible control of hopping sites makes oligosilanes a new class of hole transport materials.