Layer-by-Layer Assembled Oxide Nanoparticle Electrodes with High Transparency, Electrical Conductivity, and Electrochemical Activity by Reducing Organic Linker-Induced Oxygen Vacancies

Solution-processable transparent conducting oxide (TCO) nanoparticle (NP)–based electrodes are limited by their low electrical conductivity, which originates from the low level of oxygen vacancies within NPs and the contact resistance between neighboring NPs. Additionally, these electrodes suffer from the troublesome trade-off between electrical conductivity and optical transmittance and the restricted shape of substrates (i.e., only flat substrates). An oxygen-vacancy-controlled indium tin oxide (ITO) NP-based electrode is introduced using carbon-free molecular linkers with strong chemically reducing properties. Specifically, ITO NPs are layer-by-layer assembled with extremely small hydrazine monohydrate linkers composed of two amine groups, followed by thermal annealing. This approach markedly improves the electrical conductivity of ITO NP-based electrodes by significantly increasing the level of oxygen vacancies and decreasing the interparticle distance (i.e., contact resistance) without sacrificing optical transmittance. The prepared electrodes surpass the optical/electrical performance of TCO NP-based electrodes reported to date. Additionally, the nanostructured ITO NP films can be applied to more complex geometric substrates beyond flat substrates, and furthermore exhibit a prominent electrochemical activity. This approach can provide an important basis for developing a wide range of highly functional transparent conducting electrodes.