Enhanced hole injection in a polymer light emitting diode using a small molecule monolayer bound to the anode

A monolayer of quarterthiophene-2-phosphonate (4TP) was chemically bound to the surface of indium tin oxide (ITO) and was then p-doped with the strong acceptor, tetrafluorotetracyanoquinodimethane (F4-TCNQ). This interface modification strongly reduced the barrier for hole injection compared to unmodified ITO. This doped monolayer surface treatment was also superior to the commonly used anode coating poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PPS) at driving voltages above 5.2 V.