Transparent organic light-emitting diodes using metal acethylacetonate complexes as an electron injective buffer layer

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Abstract
We studied transparent organic light-emitting diodes, which had a transparent top electrode deposited by sputtering, for possible application to a transparent light-emitting display. In the fabrication of a transparent electrode on an organic layer, steps must be taken to reduce the damage incurred by the organic layer during the sputter deposition process. We report the results of our study where we found that we could reduce the damage to the organic layer by suppressing the temperature rise of substrate resulting from the intermittent plasma irradiation. We also found that a thin film of metal acethylacetonate complexes [Mt(acac)2] is useful as a buffer layer to prevent an underlying emission layer from incurring damage in the sputter process. In previous reports, a thin film of copper phthalocyanine (CuPc) was used as an electron injective buffer layer. However, the absorption of the CuPc Q bands at λ=620 and 665 nm decreased the total optical transmission of the device. Transmittance in the visible region of our device reached ∼90%, because Mt(acac)2 has no absorption properties that reduce the transmittance of visible light. The device using Ni(acac)2 as a buffer layer showed better electron injection properties and luminance of 1500 cd/m2 than the one using CuPc.