Discovering the Secret Life of Solids: Catching Materials Evolution in Real Time

Metal halide perovskites are remarkable materials with the ability to convert sunlight into electricity, emit colorful light, and detect radiation. However, making them typically requires harmful solvents, and the process of their formation has remained largely invisible to scientists. To address this, researchers combined an old technique—mechanochemistry, which involves grinding solids to trigger chemical reactions—with modern optical spectroscopy. By replacing traditional milling jars with transparent quartz and using a Time-Lapsed In Situ (TLIS) spectrometer, they created a system that allows scientists to observe perovskite formation in real-time, capturing every millisecond of change. This new tool acts like a high-speed camera for materials, revealing how disordered solid precursors evolve into structured, functional crystals.

Figure 1: The TLIS Spectrometer and Its Applications, see description below.

Using the TLIS spectrometer, the team made several key discoveries. They observed how a promising solar cell material, formamidinium lead triiodide (FAPbI₃), quickly degrades from a stable black phase to an ineffective yellow phase, but adding methylammonium (MA⁺) helped slow this process significantly. In another case, a lead-free perovskite unexpectedly "self-healed" over the weekend, improving its ability to emit light due to the slow migration of chloride ions within the solid. They also enhanced tin-based perovskites, which are more environmentally friendly than lead-based ones but degrade quickly, by creating a protective chloride shell. This breakthrough not only improves stability but also opens new possibilities for biomedical imaging. The ability to observe materials evolving in real time allows scientists to develop and optimize new materials much faster, reducing research time from months to days while eliminating the need for hazardous solvents. This work paves the way for more sustainable, efficient material discovery across industries like solar energy, electronics, and even food science.

Figure 1: The TLIS Spectrometer and Its Applications

Figure 1 illustrates how the Time-Lapsed In Situ (TLIS) spectrometer helps scientists observe changes in materials during chemical reactions in real-time.

• (a) Experimental Setup: The diagram shows the TLIS spectrometer, which includes a light source, a spectrometer, and a computer interface for collecting data. The system measures how materials interact with light while undergoing changes.
• (b) Diffuse Reflectance Mode: This mode tracks how perovskites like FAPbI₃ transition between different phases over time. The data reveals how the material shifts from its efficient black form (α-phase) to an unstable yellow form (δ-phase) by measuring changes in how much light the material absorbs.
• (c) Photoluminescence Mode: This mode detects how materials emit light after being excited. The graph shows how a lead-free perovskite, Cs₂Na₀.₉Ag₀.₁BiCl₆, changes in brightness due to ball milling (a grinding process) and later storage. This effect is linked to the slow movement of chloride (Cl⁻) ions, which help repair defects in the material, improving its ability to emit light.

These insights help scientists better understand how perovskites form and evolve, leading to more stable and efficient materials for solar cells, electronics, and optical applications.

Original Publication

SpringerCommunities
When a Forgotten Experiment Revealed the Secret Life of Solids
Published in Chemistry, Materials, and Sustainability, Feb 05, 2025
Xiao Yonghao, Research Fellow, Nanyang Technological University