We all know that we need more energy to power our growing world. But how can we get it in a clean and cheap way? One possible answer is using materials that can turn sunlight into electricity. These materials are called semiconductors, and they have been getting better and better over the years. One of the most promising semiconductors is called perovskite, which is very efficient, easy to make, and has other cool features. But there is a catch: perovskite is very sensitive to things like light, water, heat, air, and some liquids. This means that it can easily break down and lose its power. How can we use perovskite to solve our energy problems if it can’t handle the environment it’s supposed to work in?
Luckily, scientists have been working hard to make perovskite more stable and durable. One way they do this is by mixing perovskite with other materials, such as organic molecules, plastics, glasses, and metal-organic frameworks (MOFs). These mixtures, called composites, can often perform better than perovskite alone, but they also have some challenges. For example, when we put these composites into devices like lights or solar panels, the contact between different materials can affect how well they work. To make better devices, we need to understand what happens at these contacts, or interfaces. But studying these interfaces is not easy. Some composites are too unstable to last long enough for testing. Others are too similar to tell apart the different materials.
That’s why we are using a special kind of composite, made of perovskite and MOF hybrid glass. This composite has many advantages: it has a lot of variety, it has a clear contrast between the materials, and it is very stable. This makes it ideal for studying the interfaces using advanced techniques, such as electron microscopy, X-ray analysis, and Terahertz spectroscopy. These techniques can reveal important information about the structure, chemistry, and physics of the interfaces, which can help us design more efficient and stable devices. This composite is also very good at resisting the environment, so we can store it without worrying about it breaking down.
We made different kinds of composites by mixing perovskite and MOF hybrid glass with different amounts and heating them at different temperatures. Then we measured how bright they glow when exposed to light. The brightest one was made of 25% perovskite and 75% MOF hybrid glass, and heated at 275 °C. We found that if we use more than 40% perovskite, the composites lose their glow quickly. We also used a special microscope to see where the light was coming from. We saw that the perovskite particles were very small and scattered in the MOF hybrid glass. The light they emitted was different from the light of the whole composite. We also noticed that the brightness of the light did not depend on the size of the particles, which means that there was something else going on.
We wanted to know more about what happens at the interface, where the perovskite and the MOF hybrid glass touch each other. This is important because it affects how bright the composite glows. We used some fancy techniques to see the details of the interface at the atomic level. We found that the interface has a different chemical environment than the rest of the composite. This changes the shape of the perovskite peaks, which are related to its light emission. The interface also has some new bonds between different atoms, like Zn-I, Pb-N, and Pb-Zn. These bonds help to reduce the surface traps, which can lower the brightness. We also found that there is more iodine outside the perovskite than inside. This means that the iodine is moving from the perovskite to the MOF hybrid glass. We also saw that the interface has some short-range order, but not long-range order. This means that the atoms are arranged in a random way, not in a regular pattern. These results show that the interface is not just a simple contact, but a complex region with its own structure and chemistry.
This paper introduces a novel approach to control the formation of an interdiffusion alloying layer by sintering. This layer stabilises the optoelectronic phases of CsPbI3 and passivates its trap states. On the other hand, alloying can create non-stoichiometric perovskite regions and quench PL during subsequent high-temperature sintering, despite preserving short-range rigid halide structures in the nanometer-thick alloying layer. This study has significant implications for the fundamental understanding of defect formation and control in perovskite materials as well as the design of related devices through interfacial engineering. Our research suggests that achieving a perfect crystal structure is not a prerequisite for obtaining remarkable performance in this particular class of semiconductors. Rather, further research efforts should be focused on interfacial engineering, considering the different diffusion behaviours of various perovskite components.