Exciton Science/Gavan Mitchell & Michelle Gough 

In our move towards net zero, solar panels are essential technology. We have been seeing a decrease in silicon-based solar panel costs, but there seemed to be no significant efficiency improvements until perovskite solar panels popped up. They aren't supply-limited and have a more straightforward, lower-carbon process.

But while they are cheaper to manufacture and are more flexible, they haven't become commercially viable yet as they can be too unstable when exposed to heat, light, moisture, and oxygen.

This is where Jamie Laird's device comes in. A Research Fellow at the ARC Centre of Excellence in Exciton Science and the University of Melbourne, Laird invented the new machine for testing the defects in perovskite solar cells, the first of its kind anywhere in the world.

It was a do-it-yourself device that started as a hobby and took off during Covid-19; and now it could help unlock the next generation of solar energy, including advanced technology for space missions.

Laird’s work was published in the journal Small Methods.

The device, an example of micro-spectroscopy, is a combination of a microscope and a special laser. It produces pictures and maps of the defects within solar cells, thereby revealing where the cells are losing power or efficiency over time and use. What's better is it also provides data to indicate why.

The technique was originally intended to analyze minerals and was solely meant as a personal project for Laird.

But when he joined Exciton Science, Laird realized that his gadget could be a handy tool to help his colleagues and other solar cell researchers around the world. It would help them better understand the issues that kept perovskites from fulfilling their "exciting promise".

"The basis of the technique is microscopy but merging it with frequency analysis. We use a laser beam and we focus on a spot and scan across the device to measure the quality of the solar cell. This new method allows us to do imaging analysis of whole or complete solar cells and look at how they perform, how they change with time and aging, and how good a solar cell they are," Laird said in a release.

Other than partners at Monash University, a team from Oxford University has already sent samples of cutting-edge prototypes to be tested by Laird's machine. Members of the University of Sydney working on experimental solar cells for satellites and other space vehicles are also on the waiting list.

"You can’t have a solar cell that decomposes quickly when it’s meant to last 20 years in the field. This is a missing link in the repertoire of techniques we have to throw at that problem," Laird added.

In this report, a large-area laser beam-induced current microscope that has been adapted to perform intensity modulated photocurrent spectroscopy (IMPS) in an imaging mode is described. Microscopy-based IMPS method provides a spatial resolution of the frequency domain response of the solar cell, allowing correlation of the optoelectronic response with a particular interface, bulk material, specific transport layer, or transport parameter. The system is applied to study degradation effects in back-contact perovskite cells where it is found to readily differentiate areas based on their markedly different frequency response. Using the diffusion-recombination model, the IMPS response is modeled for a sandwich structure and extended for the special case of lateral diffusion in a back-contact cell. In the low-frequency limit, the model is used to calculate spatial maps of the carrier ambipolar diffusion length. The observed frequency response of IMPS images is then discussed.