SPACE-CHARGE LIMITED INJECTION INTO TRAP-FREE POLYMERS

The existence of trap-free unipolar charge transport polymers designed for application in electrophotographic receptors is exploited in a te st for distinguishing ohmic from emission limited contacts. The test i nvolves comparison of dark injection transients created by the applica tion of a voltage step with time-of-flight transients obtained by UV p hotoexcitation, and comparison of steady-state dark-injection currents with the current values predicted for space charge limited currents i n these materials. Contacts are characterized between electrodes such as carbon-black filled polymer, gold, indium-tin oxide and aluminum, a nd trap-free hole transport media, enyl-N,N'-bis(3-methylphenyl)-[1,1' -biphenyl]-4,4' -diamine (TPD) and a condensation polymer containing T PD transport-active units (PTPB). Evidence is provided that many of th ese contacts are truly ohmic.