Future of High Efficiency Perovskite Solar Cells Shines a Little Brighter

The researchers used a powder technique method to create a high quality version of FAPbI3. First they mixed formamidinium acetate (FAAc) with hydriodic acid (HI). PbI2 was then added. The mixture was then heated to 90 degrees Celsius. In the last step, any remaining impurities or unreacted materials were dissolved in water and filtered off. Image credit: OIST

Solar cells, which convert sunlight into electricity, have long been part of the global vision for renewable energy. Although individual cells are very small, when scaled up into modules they can be used to charge batteries and power lamps. Lined up in a row, they could one day be the primary energy source for buildings. However, the solar cells currently on the market use silicon, which makes them expensive to manufacture compared to more traditional power sources.

This is where another, relatively new material comes into play – metal halide perovskite. Embedded in the center of a solar cell, this crystalline structure also converts light into electricity, but at a much lower cost than silicon. In addition, perovskite-based solar cells can be made with both rigid and pliable substrates, making them not only cheaper but also lighter and more flexible. However, to have real potential, these prototypes must increase in size, efficiency and lifespan.

In a new study published in Nano Energy, researchers from the Department of Energy Materials and Surface Science, led by Professor Yabing Qi at the Okinawa Institute of Science and Technology Graduate University (OIST), have now shown that manufacturing one of the raw materials is based on Any other way necessary for perovskites could be the key to the success of these cells.

A proof-of-concept device developed by the OIST Energy Materials and Surface Sciences Unit uses a perovskite solar module to charge a lithium-ion battery. Image credit: OIST

“In perovskites there is a necessary crystalline powder called FAPbI3 that forms the absorber layer of the perovskite,” explained one of the lead authors, Dr. Guoqing Tong, postdoctoral fellow in the department. “In the past, this layer was made by combining two materials – PbI2 and FAI. The reaction that takes place produces FAPbI3. But this method is far from perfect. Often remains of one or both of the original materials are left over, which can impair the efficiency of the solar cell. “

To get around this, the researchers synthesized the crystalline powder using a more precise powder technique. They also used one of the raw materials – PbI2 – but also included additional steps that included heating the mixture to 90 degrees Celsius and carefully dissolving and filtering out residues. This ensured that the resulting powder was high quality and structurally perfect.

Different sizes of perovskite solar cells and modules

The OIST Unit Energy Materials and Surface Sciences works with perovskite solar cells and modules of various sizes. Image credit: OIST

Another advantage of this method was that the stability of the perovskite increased over different temperatures. When the absorber layer of the perovskite was formed from the original reaction, it was stable at high temperatures. However, it turned from brown to yellow at room temperature, which was not ideal for absorbing light. The synthesized version was brown even at room temperature.

In the past, researchers have created a perovskite-based solar cell with more than 25% efficiency that is comparable to silicon-based solar cells. However, to get these new solar cells beyond the laboratory, larger size and long-term stability are required.

“Laboratory-scale solar cells are tiny,” says Prof. Qi. “The size of each cell is only about 0.1 cm2. Most researchers focus on these because they are easier to create. But in terms of applications, we need solar panels that are much larger. The service life of the solar cells must also be taken into account. Although an efficiency of 25% was previously achieved, the service life was a few thousand hours at the most. After that, the efficiency of the cell began to decrease. “

With the synthesized crystalline perovskite powder, Dr. Tong together with postdoc Dr. Dae-Yong Son and the other scientists in Prof. Qi’s department found a conversion efficiency of over 23% in their solar cell, but the lifespan was more than 2000 hours. When they were scaled up to solar modules of 5x5cm2, they still achieved an efficiency of over 14%. As a proof-of-concept, they made a device that uses a perovskite solar panel to charge a lithium-ion battery.

These results represent a decisive step towards efficient and stable solar cells and modules based on perovskite that could one day also be used outside the laboratory. “Our next step is to produce a solar module with a size of 15 x 15 cm2 and an efficiency of more than 15%,” said Dr. Tong. “I hope that one day we will be able to supply a building at the OIST with electricity with our solar modules.”

This work was supported by the proof-of-concept program of the OIST Technology Development and Innovation Center.

Reference: “Removal of residual compositions by powder technology for highly efficient formamidinium-based perovskite solar cells with an operating life of over 2000 h” by Guoqing Tong, Dae-Yong Son, Luis K. Ono, Hyung-Been Kang, Sisi He, Longbin Qiu, Hui Zhang, Yuqiang Liu, Jeremy Hieulle and Yabing Qi, May 13, 2021, Nano Energy.
DOI: 10.1016 / j.nanoen.2021.106152

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