Researchers at Oxford University and Exciton Science have developed a new way to create stable perovskite solar cells that have the potential to rival silicon’s durability.
The researchers reduced the defects of perovskite solar cells by removing the solvent dimethyl-sulfoxide and introducing dimethylammonium chloride as a crystallisation agent. This allowed the team to better control the intermediate phases of the perovskite crystallisation process, leading to thin films of greater quality and enhanced stability. Large groups of sample devices were then subjected to a rigorous accelerated ageing and testing process at high temperatures and in real-world conditions.
The new perovskite solar cells created by the team were shown to outperform the control group, demonstrating resistance to thermal, humidity, and light degradation.
The study, ‘Intermediate-phase engineering via dimethylammonium cation additive for stable perovskite solar cells,’ led by Professor Henry Snaith and Professor Udo Bach, is a strong step forward to matching commercial silicon’s stability, making perovskite-silicon tandem devices a promising candidate for becoming the dominant next-generation solar cell.
Creating the new perovskite solar cells
The formamidinium-caesium perovskite solar cells were created using the new synthesis process, which enhanced their stability.
Oxford University PhD student Philippe Holzhey, a Marie Curie Early Stage Researcher and joint first author on the work, said: “It’s really important that people start shifting to realise there is no value in performance if it’s not a stable performance.
“If the device lasts for a day or a week or something, there’s not so much value in it. It has to last for years.”
The researchers found that the best device operated above the T80 threshold for over 1,400 hours under simulated sunlight at 65°C. T80 is a common benchmark within the research field, being the time it takes for a solar cell to reduce to 80% of its initial efficiency.
Beyond 1,600 hours, the control device fabricated using the conventional dimethyl-sulfoxide approach stopped functioning. However, devices fabricated with the new, improved design retained 70% of their original efficiency, under accelerated ageing conditions.
The same degradation study was performed on a group of devices at 85°C, with the new perovskite solar cells again outperforming the control group.
From the data collected from this, the team calculated that the new cells age by a factor of 1.7 for each 10°C increase in the temperature they are exposed to, which is close to the 2-fold increase expected of commercial silicon devices.
Dr David McMeekin, the corresponding and joint first author on the paper, said: “I think what separates us from other studies is that we’ve done a lot of accelerated aging. We’ve aged the cells at 65°C and 85°C under the whole light spectrum.”
The number of devices used in the study is also significant, with many other perovskite solar cell research projects being limited to just one or two prototypes.
“Most studies only show one curve without any standard deviation or any kind of statistical approach to determine if this design is more stable than the other,” Dr McMeekin added.
The researchers want their work to encourage more research on the intermediate phase of perovskite crystallisation as an important factor in achieving greater stability and commercial viability.
Perovskite solar cells are far cheaper to make than silicon photovoltaics, as they are artificially synthesised in laboratory conditions, and produced with greater flexibility and a tunable band gap.
Over the last decade, these cells have unexpectedly emerged, reaching impressive power-conversion efficiencies of over 25%.
However, researchers have previously focused too much on creating the most efficient perovskite solar cell, instead of resolving the fundamental problems inhibiting the material from being used in widespread commercial applications.
Compared to silicon, perovskite solar cells can degrade rapidly in real-world conditions, with exposure to heat and moisture causing damage and negatively impacting device performance.
Solving these stability issues is vital for perovskite solar cells to be able to match commercial silicon photovoltaics, which is what the researchers have been able to demonstrate with their new study.