Could you introduce yourself to our readers and tell us about your current position and research activities?
My name is Jack Jasieniak and I am a professor of materials science and engineering at Monash University. I am also the Pro Vice-Chancellor of Research Infrastructure at Monash. My research concerns the development of next-generation materials for new energy technologies as well as advanced sensing applications. Our most recent activity is a collaboration between Monash University and the Commonwealth Scientific and Industrial Research Organization (CSIRO), which is a key partner focused on achieving large-scale printed perovskite devices.
Could you summarize the results of your recent research?
When you look at a solar cell in general, it is a multilayer device. a perovskite device generally has five layers. It is important to understand the materials in each of these layers and how each of these layers is then interconnected. Recently, we have focused on a layer called the electron transport layer, which allows electrons to be selectively transported from a solar cell material. For perovskite devices, you have a metal halide perovskite as the absorber layer, which is sandwiched between two selectively charged layers, one for electrons (negative charges) and the other for holes (positive charges), and covered with appropriate electrodes. Once you absorb the light, it creates electrons and holes within the perovskite, which then must be efficiently channeled through the appropriate charge transport layer to reach the electrodes. Thus, the electron transport layer plays an important role in determining half of the function of this device. Developing such a layer that is printable, scalable and stable is critical and something we have managed to achieve. Image Credit: Audio and Advertising/Shutterstock.com
What are nanoparticle inks?
Nanoparticle inks are formulations where you have nanocrystals dispersed in a specific liquid along with appropriate stabilizers and additives that allow printing and provide the right kind of structure to the printed form. Now, we are looking at taking a “one-pot approach” to developing easily compoundable inks. In this particular case, we have focused on developing tin oxide inks using tin-based salts in an alcohol mixture consisting of benzyl alcohol and a small amount of ethanol to provide some additional polarity. We then applied microwaves to this salt solution to induce heat, which drove a chemical reaction and the formation of tin oxide. The beauty of this reaction is that microwaves cause this transformation. Benzyl alcohol adsorbs on the surface of the nanocrystals and provides a clean passivation layer, which prevents the nanoparticles from agglomerating effectively and allows them to disperse. By doing this, you effectively have a fast and very high conversion rate that is also very easy. Plus, we’ve broken down how you can use this ink directly in your printing process. So not only have you made your particles, but you’ve made a dispersion that is very, very stable. You can take it, dilute it with suitable solvents and then use it directly in your printer. In our case, we used slot-dye printing to demonstrate the concept. Printed perovskite devices (left) and the cross-sectional electron micrograph showing the individual layers, (right), including the thin tin oxide electron transport layer. Image source: Jacek Jasieniak
The slot-dye method, also known as roll-to-roll, is commonly associated with newspaper printing. why was this approach used to make solar cells?
Slot-dye is a simple approach as it allows the ink to flow efficiently through a nozzle positioned above a moving printing surface. By controlling the rate of substrate movement, nozzle height, as well as the rate of liquid addition, you can control the thickness of the layer inside the device to a high degree. This creates a scalable approach to obtain simple structures suitable for thin-film solar cells integrated as modules. This is because printed modules are essentially multi-layered structures that are slightly offset in some of the layers. Slot-dye allows you to print such simple linear features and displacement is relatively simple.
Did the team encounter challenges or limitations in using this approach?
There are certainly some challenges to using the slot-dye method. For example, you need to develop ink formulations well so that they allow the flow and drying conditions to be correct and bond to subsequent layers. Nevertheless, groove dyeing is a very versatile approach and is considered as a truly progressive approach for developing thin film solar cells using printing approaches. Image credit: DJ Srki/Shutterstock.com
Metal halides are reported as promising materials for solar cells. What properties of tin oxide, in particular, made it particularly suitable for this research? Would you consider any other materials in future research?
Tin oxide is a suitable charge transport material because it has a high lattice energy, making it very stable as a chemical compound. It also crystallizes at a moderate temperature making it feasible for these types of reactions. Due to its high electron mobility, tin oxide can charge transport very efficiently and acts as a selective electron transport material very well. Its energy levels are suitable for use in metal halide perovskite solar cells, particularly those with a near-infrared band gap. There are alternative materials that people commonly use for electron transport layers. TiO2 (titania) is an example, but requires a much higher temperature to crystallize. This is a challenge to overcome, so if one could do it at a lower temperature, that would be beneficial for printing. It’s hard to say whether titania would ultimately be a better or worse material for printed perovskite solar cells, but it would certainly be an interesting comparison.
What do you think are the main obstacles limiting the translation of high-performance perovskite solar cell research into actual industrial practice and mass manufacturing?
Most perovskite research is done in devices that are not compatible with mass production. As a result, a lot of innovation is focused on developing high-performance, sometimes high-stability devices using techniques that are, frankly, unrelated to scale devices. A practical example is the deposition of inks deposited using a conventional small-scale method such as spin coating compared to something that is fully scalable such as groove coating. These two approaches with the same ink will exhibit different flow characteristics, drying characteristics, and final build properties. I think there needs to be a transition in this whole field away from a focus on purely high performance to a focus on high performance, using related techniques that allow for realistic scalability. However, although this transition is important, it is not an easy one for the research community to make, because these techniques are, frankly, much more difficult to deposit and master. So this move is really based on key partnerships with labs that have access to and expertise in this equipment, and understanding how quickly we can translate small-scale device development into scalable techniques.
How did your partnership with CSIRO begin and what benefits has it brought to this research?
Before joining Monash in 2015, I was a team leader at CSIRO, the Commonwealth Scientific and Industrial Research Organisation.
It is a government research laboratory here in Australia and is heavily focused on translational applied research to address industry issues and bring devices to commercial stages. I already had very strong links with CSIRO, particularly in the group I was working in, which was about printed electronics.
In this particular area, we have joined forces to look at developments around printed perovskites through facile processing, meaning no special environments.
Partnerships with organizations such as CSIRO are critical because they bring this industry perspective. In this case, they brought their prototype, slot-die systems with roll-to-roll processing units with integrated drying, heating and monitoring devices. Such a design makes it possible to cross the bridge between small and large scale, which I think is a really big step.
What are the next steps for this research?
One of the areas in which we have an active program is solar window technologies. Solar windows can be leveraged from similar types of structures, perovskites, and can certainly leverage the printing approaches we’ve shown this ink in. The next set of work will look at understanding how we can develop printed structures that can function as solar window technologies. As a first point of reference, these can be as a laminate or a more complete feature of a double-glazed configuration. It doesn’t need to be flexible, but it needs to have that high-performance functionality while still allowing enough visible light to pass through with long-term stability. There is a huge market in this space that is growing exponentially. By 2025, reports indicate that this market will grow to be in the order of five, 6 billion USD. This is a niche market compared to global PV like silicon, but it’s one that will continue to grow.
About Professor Jacek Jasieniak
Jack…
