Adrian Paul Burden

Au-ITO anode for efficient polymer light-emitting device operation

A thick gold layer is deposited on indium tin oxide (ITO) to improve the interface quality between the ITO anode and the organic layer in organic light-emitting diodes (LEDs). With this improvement, the device with structure ITO/Au/hole-transport-layer(HTL)/poly(p-phenylenevinylene)/Ca/Ag, achieved a lower turn-on voltage from 4 V to about 1.6 V and an increase in luminescence intensity by more than a factor of two at the same voltage. The work function of the Au facilitates the formation of an ohmic contact and good mechanical adhesion to the HTL. The experimental results suggest that the ITO contact limits the supply of current for radiative recombination. The improvement of the device performance is due to the smoother Au surface and the matching of the Au work function with the highest occupied molecular orbital level of adjacent HTL layer.

Indium-tin-oxide-free organic light-emitting device

Sapphire substrates coated with a gold (Au) layer in place of indium-tin-oxide (ITO) on glass substrates are used as hole-injecting anodes in organic light-emitting devices (OLEDs). Due to the unique quality of the sapphire/Au interface and the match of the Au work function with the highest occupied molecular orbital level of the adjacent hole transport layer (HTL) and the smoothness of the interface, the ITO-free OLED, with the structure sapphire/Au/HTL/poly(p-phenylenevinylene)/Ca/Ag, achieved an increase in current efficiency by more than a factor of three. In addition, the flawless sapphire substrate and anode/polymer interface make dark nonemissive areas decrease in number and area. The diodes show substantially slower degradation, and the lifetime in air increases by a factor of two or more.

Blocking Impurities in Organic Light Emitting Device by Inserting Parylene Interlayer

Secondary-ion mass spectrometry is used to study ion diffusion from a substrate into an organic film, which is considered as one of the reasons for organic-light-emitting-device degradation and instability. Results show that a 1 µm-thick parylene layer inserted between an indium–tin–oxide (ITO) anode and a soda-lime glass substrate effectively controls the diffusion of sodium, potassium, silicon and sulphur ions from the substrate to the device. The effect is the same as that in the case of using a plastic substrate which is sodium- and potassium-free. Also a 3 nm-thick parylene layer grown in between an ITO anode and a hole transport layer (HTL) not only shows improvement in device performance, but also is capable of blocking impurities such as sodium, potassium, silicon and sulphur ions. This study shows that the use of a parylene layer is effective for controlling contamination coming from the substrate.