Unique Mono-Core Growth to Realize Single-Crystal Perovskite Films for Highly Efficient and Stable Optoelectronic Devices

Professor Choy, Wallace Chik Ho   (Principal Investigator (PI))

Professor Ke Xiaoxing   (Co-Investigator)

Professor Yin Wanjian   (Co-Investigator)

Dr Yu Fei   (Co-Investigator)

36

2020-01-01

2022-12-31

462342

Unique Mono-Core Growth to Realize Single-Crystal Perovskite Films for Highly Efficient and Stable Optoelectronic Devices

metastable state, mono-core growth, nucleation and growth, perovskite films, single crystals

Photonics

Engineering (E)

17201819

General Research Fund (GRF)

2019

Completed

1) Enlarging perovskite grains beyond the film thickness regime while maintaining good film quality. Perovskite grain size is limited to the film thickness by the ""specimen thickness effect"". Meanwhile, grain enlargement in crystallization/recrystallization inevitably leads to poor film quality due to surface tension-driven shrinkage. To simultaneously achieve grain enlargement and maintain good film quality in perovskites (e.g., good morphology, well-packed grains, low density of voids/cracks, etc.), we will study exaggerated grain growth in perovskites and control the growth by modifying the adjacent layers of perovskites. We will also study the grain size enlargement to understand the growth mechanism. Consequently, we target to enlarge grains while maintaining high film quality, and obtain the foundational knowledge for improving the quality of polycrystalline perovskite films and device performances; 2) Unique mono-core growth for substrate-integrated SGC perovskite films. By leveraging the know-how on exaggerated grain growth, we propose a new concept of mono-core growth in MVAD for controlled growth of SGC perovskite films from one small core to a large area in a metastable state triggered by exotic energy perturbation. The ""mono-core"" concept relies on the fact that thermodynamically less-stable small grains are swallowed by large grains during the growth of a plurality of grains (which were formed after energy perturbation). We will study the perovskite transformation in MVAD. Then the stable state will be studied experimentally as described in ""Plan and Methodology, Part II-2(b)"". We will promote one core growth to form SGC films and eliminate polycrystalline perovskites by avoiding the transformation at unstable state where multi-nucleation occurs. Perovskite films made by MVAD are compatible with substrates because of the bridging effect of inorganic halide films. Thickness of perovskite SGC films will be controlled by tuning film formation parameters of the inorganic layers. Consequently, we aim to achieve different on-substrate crystalline perovskite films for device applications, and gain the knowledge of nucleus formation, grain growth and crystal film formation; 3) Fundamental investigation on interfaces. We will comprehensively study the interfaces (i.e., GBs and interfacial contacts between perovskites and interface layers), which are critical for understanding grain growth and optimizing device performances and stability. Notably, GB migration holds the key to exaggerated grain growth and mono-core growth of the crystalline films. By combining with the understanding of grain growth in Objective (1), we will investigate GB migration and convection in quasi-solid films. We will then study GB and bulk diffusion of typical ions (i.e., organic cations, inorganic anions and metal ions) in crystalline perovskite films. Meanwhile, we will study the interfaces to achieve the good interfacial contacts with decent electrical transport/collection. Consequently, we will conclude the influences of GBs, defects, SGC quality, and interfaces targeted for exploring performance limits of SGC perovskite devices, which also address the myth of low efficiency of SGC perovskite devices nowadays.