Charge injection and transport in spiro-linked arylamine compounds

We use dark-injection space-charge-limited current (DI-SCLC) and admittance spectroscopy (AS) to study charge injection and transport properties of spiro-linked arylamine compounds. Examples are spiro-linked TPD and spiro-linked NPB which are both important amorphous hole transporters for organic light-emitting diodes (OLEDs). With PEDOT:PSS as the hole-injection layer, the contact is demonstrated to be generally Ohmic. Both techniques can be used to measure the carrier mobilities of thick films (>μm) of spiro-compounds. DI-SCLC can be viewed as a pulse technique whereas AS can be treated as an ac technique. For the hole mobilities evaluation of the spiro-compounds, both techniques are in general agreement to each other. However, for the case of the thinner films of less than 1μm, AS is superior over the DI-SCLC technique. The advantages of AS will be highlighted. It appears that AS is broadly applicable to characterize transport properties of organic thin films.