A novel use of solar panel material can substantially upgrade durability

A collaborative research effort between scientists at universities in the U.K. and Japan has found the secret to the 'Achilles heel' of perovskites, a low-cost alternative for making cells for solar panels, Phys.org reported. This could pave the way for durable photovoltaics in the near future. 

Tapping highly abundant solar power is one of the methods countries are using in their bid to move away from fossil fuels. Manufacturing solar panels at scale requires specialized infrastructure for silicon processing that comes with a heavy capital outlay. This is reflected in the high cost of solar panels, which has become a major impediment in transitioning to this form of renewable energy.

Perovskite, a naturally occurring mineral of calcium titanate has been found to be a cheaper alternative to silicon for making photovoltaic cells but the road to using them commercially is not that straightforward. 

The problem with perovskites

A typical solar panel made using silicon typically lasts for 20-25 years. To compete with the high durability of these panels, perovskite-made panels need to remain operable for at least a decade. However, this has not been achieved even in research settings. At a commercial scale, the performance of these panels is expected to drop further. 

Researchers at the University of Cambridge in the U.K. and the Okinawa Institute of Science and Technology (OIST) in Japan, therefore, studied the perovskite-made solar panels to their nanomolecular scale to understand why these panels degrade over time. 

Previous research by the team to understand why the performance of perovskite-photovoltaics fails over time led them to a phenomenon called carrier traps. Using electron microscopy, the researchers were able to observe the changes that were occurring in these carrier traps and now, they're able to link them to the longevity of the solar cell. 

The solution to making sustainable solar cells 

Perovskites can be prepared in liquid ink and printed to form a thin layer of solar cells. By slightly changing the chemical composition of the perovskites, the researchers were able to change how the perovskite film forms while being printed and contain the formation of the carrier traps. The researchers expect photovoltaics made with these changes to remain operable for longer periods of time and bring us closer to commercially available perovskite photovoltaic devices soon. 

"Manufacturing processes need to incorporate careful tuning of the structure and composition across a large area to eliminate any trace of these unwanted phases," said Dr. Sam Stranks from Cambridge University who led the research. "This is a great example of fundamental science directly guiding scaled manufacturing."

Manufacturing perovskite photovoltaics does not require the costly infrastructure that silicon photovoltaics do and can be set up in areas that do not have facilities for processing silicon. This is a major boon for low-and middle-income countries that are looking to transition to solar energy, the press release said. 

The researchers published their findings in the journal Nature.

Abstract

Understanding the nanoscopic chemical and structural changes that drive instabilities in emerging energy materials is essential for mitigating device degradation. The power conversion efficiency of halide perovskite photovoltaic devices has reached 25.7% in single junction and 29.8% in tandem perovskite/silicon cells^1,2, yet retaining such performance under continuous operation has remained elusive³. Here, we develop a multimodal microscopy toolkit to reveal that in leading formamidinium-rich perovskite absorbers, nanoscale phase impurities including hexagonal polytype and lead iodide inclusions are not only traps for photo-excited carriers which themselves reduce performance^4,5, but via the same trapping process are sites at which photochemical degradation of the absorber layer is seeded. We visualize illumination-induced structural changes at phase impurities associated with trap clusters, revealing that even trace amounts of these phases, otherwise undetected with bulk measurements, compromise device longevity. The type and distribution of these unwanted phase inclusions depends on film composition and processing, with the presence of polytypes being most detrimental for film photo-stability. Importantly, we reveal that performance losses and intrinsic degradation processes can both be mitigated by modulating these defective phase impurities, and demonstrate that this requires careful tuning of local structural and chemical properties. This multimodal workflow to correlate the nanoscopic landscape of beam sensitive energy materials will be applicable to a wide range of semiconductors for which a local picture of performance and operational stability has yet to be established.