A General Method: Designing a Hypocrystalline Hydroxide Intermediate to Achieve Ultrasmall and Well‐Dispersed Ternary Metal Oxide for Efficient Photovoltaic Devices

Abstract

Solution‐process fine metal‐oxide nanoparticles are promising carrier transport layer candidates for unlocking the full potential of solution process in solar cells, due to their low cost, good stability, and favorable electrical/optical properties. However, exotic organic ligands adopted for achieving small size and monodispersion can mostly cause poor conductivity, which thus impedes their electrical application. In this work, a concept of constructing a hypocrystalline intermediate is proposed to develop a general method for synthesizing various ternary metal oxide (TMO) nanoparticles with a sub‐ten‐nanometer size and good dispersibility without exotic ligands. Particularly, a guideline is summarized based on the understandings about the impact of metal ion intercalation as well as water and anion coordination on the hypocrystalline intermediate. A general method based on the proposed concept is developed to successfully synthesize various sub‐ten‐nanometer TMO nanoparticles with excellent ability for forming high‐quality (smooth and well‐coverage) films. As an application example, the high‐quality films are used as hole transport layers for achieving high‐performance (stability and efficiency) organic/perovskite solar cells. Consequently, this work will contribute to the development of TMO for large‐scale and high‐performance optoelectronic devices and the concept of tailoring intermediate can leverage the fundamental understandings of synthesis strategies for other metal oxides.