The mass production of high-performance perovskite solar cells could soon become easier now that researchers in Taiwan and the US have discovered a simple alteration to the manufacturing process. The technique was developed by Leeyih Wang at National Taiwan University and colleagues, who showed that it boosts both the power conversion efficiency and operational lifetime of a perovskite mini-module. Their innovation could soon open new routes towards the large-scale manufacture of perovskite solar cells, making them a strong competitor to existing silicon-based cells.
Perovskite materials are widely seen as some of the most promising candidates for low-cost, large-area solar cells. Owing to their excellent optoelectronic properties, recent experiments have demonstrated conversion efficiencies as high as 22%, over areas of 0.5 cm2. So far, however, similar performances on larger scales have been hindered by the difficult manufacturing requirements of thin perovskite films.
Currently, the fabrication process usually involves dripping an antisolvent onto a perovskite precursor that has been spin-coated onto a substrate. Ideally, this technique can create films with uniform, high-quality crystal structures. However, the conditions of the process must be tightly controlled, and the antisolvent must be applied within a time window of just 9 s following the initial deposition. Otherwise, the resulting perovskite film could be rough and uneven – diminishing its performance as a solar cell. As films become larger, it becomes increasingly difficult to implement this process.
New antisolvent
To combat this issue, Wang’s team, which also included researchers at Los Alamos National Laboratory, introduced a technique that significantly broadened the post-deposition time window. They did this using sulfolane as an antisolvent, which enabled them to fabricate uniform, high-quality, and large-area perovskite films in their experiment. To investigate the molecular mechanisms responsible for this improvement, they studied the chemical reactions involved using a combination of X-ray diffraction and infrared spectroscopy.
Caffeine boosts perovskite solar cells
They found that hydrogen bonding between sulfolane molecules and perovskite precursor ions slowed down the crystallization process significantly, thereby extending the time window for antisolvent addition to 90 s. This enabled compact, highly uniform crystal structures to form in far less stringent processing conditions. To demonstrate this improvement, Wang and colleagues fabricated a perovskite solar cell mini-module with an active area of 36.6 cm2.
Their device achieved a very respectable power conversion efficiency of over 16%, and retained around 90% of its initial performance after operating for 250 hours at 50 °C – the point at which it extracted the maximum possible amount of power. This high efficiency and long operational lifetime set the stage for large-scale perovskite solar cell production, in far more flexible manufacturing conditions. Wang’s team hope that the technology could soon become widely available commercially and may even become a viable competitor to silicon-based solar cells – boosting the outlook for renewable solar energy.
The research is described in Joule.
