Low Temperature Photochemical Sol-Gel Processing of Functional Thin Films and their Applications

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The project aims to develop general methodologies for the precise control of functional inorganic thin films in their low temperature solution processing for the realization of roll-to-roll fabrication of flexible electronics. This year, it was found that solution-processed amorphous metal-organic thin film zinc(II) methoxyethoxide (ZME) acts as an efficient and stable electron injection layer (EIL) in inverted organic light-emitting diodes (iOLEDs). In contrast, crystallized ZnO obtained either by utilizing vacuum ultraviolet (VUV) light irradiation or by high temperature annealing caused a strong electron leakage, reducing device efficiency. DC capacitance analysis revealed that ag-ZME has a highly dielectric behavior, allowing it to selectively inject electrons into the LUMO of the organic layer while preventing non-emissive direct reduction of holes. Calcium(II) methoxyethoxide (CME) was also employed as an EIL for comparison and showed nearly the same performance as ZME in iOLEDs, despite its strongly insulating properties. The 4s orbitals of Ca(II) and Zn(II) in ag-CME and ag-ZME are used to regulate the electron injection, these insights offer a new design strategy that uses amorphous dielectric metal-organic thin films as EILs, which may yield high-performance, flexible, and stable electronic devices, such as iOLEDs and perovskite solar cells.