- Perovskites are predicted to be a game changer in future solar technology, but they are now declining for shorter life expectancy and efficiency as they rise to larger sizes.
- Scientists have improved the stability and efficiency of solar cell modules by mixing pioneering materials with ammonium chloride in manufacturing
- The active perovskite layer of improved solar modules is thicker and has larger specimens with fewer defects
- Both 5 x 5 cm2 and 10 x 10 cm2 the perovskite module has maintained high efficiency for over 1000 hours
Researchers at the University of Okinawa University of Science and Technology (OIST) have created perovskite solar modules with better stability and efficiency, using a new manufacturing technique that reduces defects. Their findings were published on the 25thth January 2021, year Advanced energy materials.
Perovskites are one of the most promising materials for the next generation of solar technology, with an efficiency increase of slightly between 3.8% and 25.5% in a decade. Solar cells are inexpensive to produce perovskites and have the ability to be flexible, increasing their versatility. But there are still two barriers to marketing: long-term instability and increasing difficulties.
“Perovskite material is brittle and prone to decomposition, which means that solar cells struggle to maintain high efficiency over a long period of time,” said Dr. Guoqing Tong, postdoctoral fellow in the OIST Energy Materials and Surface Sciences Unit. Yabing Qi. “And small-sized perovskite solar cells have a high efficiency and work just as well as their silicon counterparts. Once they go up to larger solar modules, the efficiency goes down.”
In a functional solar device, the perovskite is located in the middle of the layer, located between the two transport layers and the two electrodes. As the active layer of perovskite absorbs sunlight, it generates transport charges, which then flow through the transport layers to the electrodes and generate a current.
However, pinholes in the perovskite layer and defects in the boundaries between the individual perovskite grains can disrupt the flow of load carriers from the perovskite layer to the transport layers, reducing efficiency. Moisture and oxygen at these fault sites can begin to damage the perovskite layer, shortening the life of the device.
“It is difficult to increase the scale because the larger the size of the modules, the more difficult it is to create a uniform layer of perovskite and these defects become more pronounced,” explains Dr. Tong. “We wanted to find a way to manufacture large modules to deal with these problems.”
Today, most of the solar cells created have a thin layer of perovskite – they are only 500 nanometers thick. In theory, a thin layer of perovskite improves efficiency because the load carriers have less distance to travel to reach the upper and lower transport layers. But in manufacturing larger modules, the researchers found that a thin film often caused more errors and pinholes.
So the researchers decided to make it 5 x 5 cm2 and 10 x 10 cm2 solar modules with double-thickness perovskite films.
Scientists from the OIST Energy Materials and Surface Sciences Unit show solar perovskite modules in operation, powering a fan and a toy car. Credit: OIST
However, making thicker perovskite films came with its own set of challenges. Perovskites are materials that allow many compounds to react together as a solution and then crystallize.
However, scientists made efforts to dissolve a sufficient concentration of iodine lead – one of the pioneers of the materials used to form perovskite – needed for thicker films. As they found that the crystallization step was fast and uncontrollable, the thick films had many small grains, which had more grain limits.
The researchers therefore added ammonium chloride to increase the solubility of lead iodine. This allowed lead iodine to be dissolved evenly in the organic solvent, resulting in a more uniform perovskite film with much larger grains and fewer defects. Ammonia was removed from the perovskite solution, lowering the level of impurity inside the perovskite film.
Generally, solar modules measuring 5 x 5 cm2 it showed an efficiency of 14.55% in ammonium chloride-free modules, 13.06%, and they were able to work for 1600 hours – over two months – with more than 80% of this efficiency.
Larger 10 x 10 cm2 the modules had an efficiency of 10.25% and remained at high efficiency levels for more than 1100 hours, which is almost 46 days.
“This is the first time that the measurement of the life span of solar modules of perovskite has been reported, which is really exciting,” Dr. Tong said.
This work was supported by the Proof-of-Concept Program of the OIST Technology Development and Innovation Center. These results are a promising future in terms of efficiency and stability in the production of commercial-sized solar modules that are compatible with silicon.
In the next stage of the research, the team intends to further optimize its technique by manufacturing perovskite solar modules using steam-based methods rather than using a solution, and they are now trying to scale up to 15 x 15 cm.2 modules.
“Transition to 5 x 5 cm from laboratory-sized solar cells2 the solar modules were hard. Jumping into 10 x 10 cm solar modules2 it was even harder. And it will go to 15 x 15 cm2 the solar modules will be even tougher, “Dr. Tong said.” But the team is looking at the challenge. “
Reference: “90 cm scalable fabrication2 Perovskite Solar Modules> Based on an intermediate phase strategy with operational stability of 1000 h “Guoqing Tong, Dae – Yong Son, Luis K. Ono, Yuqiang Liu, Yanqiang Hu, Hui Zhang, Afshan Jamshaid, Longbin Qiu, Zonghao Liu and Yabing Qi- by., January 25, 2021, Advanced energy materials.
DOI: 10.1002 / aenm.202003712