Alloying of Lead-Free Layered Double Perovskite Nanocrystals for Tailoring Structural and Optoelectronic Properties

Popular Abstract

The race towards sustainability
In a rapidly advancing society, energy consumption has increased in tandem with the rise of digitalisation and modern lifestyles. However, the recent situation of producing energy is to use finite resources such as fossil fuels. Furthermore, the use of said resource has side effects that are highly undesirable, as it is a huge contributor towards global warming. Although other alternative energy resource, particularly nuclear energy, has become an effective low-carbon emitting energy source, a set of problems emerges for humans and the environment. The radioactive waste from nuclear plants is very harmful and requires safe disposal to avoid potential radioactive contamination of bodies of water, etc.
The duality of energy production allows us to propel our civilisation forward and improve the way of living – at the same time, if we are not careful or resourceful, we might end up getting overwhelmed by all the harmful “side-effects” of energy production. This has led scientists all over the world to explore a more sustainable, safer and cheaper approach to energy production.
To replace fossil fuels, what is the alternative energy source? Looking at nature, we can see that mother nature has already shown us another way of producing energy, that is by utilizing the energy emitted by the sun and converting the harvested solar energy into another form of energy, chemical energy. The sun, which gives out free energy, is a very excellent and sustainable candidate as our energy source. By using photocatalysts, the energy absorbed by the light can be utilized to facilitate the transformation from “common” and “low value” chemicals to industrially valuable chemicals.
One potential candidate for photocatalysis is metal-halide perovskite (MHP), of which their properties have been extensively explored in parallel to the exploration of lead (Pb)-based perovskite (LP) in solar cells. LPs have shown excellent qualities in terms of electronic and optical properties, which opens up possibilities in visible light-driven applications.
Despite the excellent properties of LPs, the material suffers from some unattractive features, particularly that LP are inherently toxic, this proves to be a major hindrance for large scale application. Another obstacle is the low stability of LPs in various environmental exposures, such as oxygen, heat and light. To address the toxicity and stability, we require a benign element and a new strategy. Tin (Sn), which is the 5th period analogue to lead, is a potential replacement for Pb, with lower toxicity but still advanced optoelectronic properties and has been further pushed out into the limelight of lead-free halide perovskites.
As such, the driving force behind this master's thesis is using Sn-based nanocrystal perovskites. The size of the crystals is selected due to the exciton Bohr radius being 5-7 nm for CsPBr3. Making the perovskites in nanoscale may reach the new perovskites’ exciton Bohr radius and as such would make the bandgap dependent on the size of the crystals, effectively tuning the band positions and possibly the absorbed wavelength of light. This modification enables the possibilities of absorbing a more precise wavelength to facilitate reactions or emitting light in a certain wavelength. The change in band positions can also serve as a tuning point where the band position can be adjusted to fit different photoreactions1.
Sn, a 5d analogue to lead and further develop its properties through the use of alloying to modify and enhance the desired properties of Sn-based perovskite, while maintaining some of the attractive features that Pb have and keeping the lower toxicity. A strategy to tune both its structure and composition is through the use of either doping. These methods incorporate another element in either a small/trace amount or substitute one of the previous components. This addition changes the electronic states of the final compound, which can either enhance the different properties, such as PL, its PEC etc. Perovskites are usually made up of many different ions, allowing the newly incorporated element to have different possible mechanisms, depending on which element substitutes, the properties are changed accordingly2-3.

• author: Tan, Niklas
• supervisor: Maning Liu; Sunardi Rahman
• organization: Department of Chemistry
• course: KEMR30 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: Lead-free halide perovskites, Doping and alloying, Layered double perovskite, Structural transition, Colloidal nanocrystals, Photoelectrochemistry (PEC), Self-trapped excitons (STE)
• language: English
• additional info: Abstract omitted due to confidential information
• id: 9202697
• date added to LUP: 2025-06-30 13:57:14
• date last changed: 2025-06-30 13:57:14