Low-dimensional copper (I) halides such as Cs₃Cu₂I₅ are attracting considerable attention in the field of photonics due to their high PLQYs. A new mixed-anion strategy is used to explore new candidates, and a new compound, Cs₅Cu₃Cl₆I₂, with a 1D zigzag chain structure is discovered. This material exhibits blue emission with a near-unity quantum yield of 95%. Moreover, the iodine-bridged 1D connectivity significantly enhances the chemical stability, compared with the pure chloride phase. The present findings provide a new perspective for developing air-stable alkali copper(I) halides with highly efficient luminescence.

2D Ruddlesden-Popper (RP) phases are an emerging class of halide perovskites that are now restricted on the only choice of organic spacers. We started the pioneering work on the explorations of all-inorganic 2D halide perovskites and found that both the specific halide choice and cation size are essential to construct a 2D framework. The finding of all-inorganic Sn- and Pb-based RP phases expands the low-dimensional halide perovskites and opens new opportunities for functionality beyond photovoltaics like optoelectronic response and radiation detection.

Operational stability is the major drawback of perovskite solar cells. We investigate the thermal degradation of inverted-structured perovskite solar cells and expose their thermal degradation mechanism through directly observing the ion diffusion of I^- and CH₃NH₃⁺ under thermal stress. Three components are believed to be beneficial for thermally stable devices: robust perovskite absorbers, halide-ion-blocking transporting layers, and chemically inert electrodes. Following these rules, we fabricated CsSnBr₂I solar cells with carbon electrodes and achieved highly stable devices against thermal stress even under 200 °C.

Interfaces are important in perovskite solar cells. To reduce the undesired interfaces (like TiO₂/HTM) and improve the desired interfaces (like perovskite/electrodes), interfacial reaction kinetics were studied and engineering work was conducted, e.g. block the notorious insertion of Li⁺ into TiO₂ with a Li-consuming modifier; control the formation of perovskite/C electrode interface using a solvent vapor assisted method.