Traditional solar cells made of silicon have been widely used to generate electricity from sunlight. However, their production requires a substantial amount of energy, and they tend to be inflexible and fragile.
Fortunately, a new type of solar cell has emerged, matching the performance of silicon cells while offering additional advantages. Notably, these cells can be printed using specialized inks and flexibly wrapped around uneven surfaces.
Our team has successfully developed the world's first rollable and fully printable solar cell using a material called perovskite. This material is significantly less expensive to produce compared to silicon. With further improvements in efficiency, this breakthrough opens the door to the large-scale manufacturing of cheaper solar cells.
Silicon solar cells, though familiar, suffer from a significant limitation. If we were to rely solely on silicon cells to meet our energy demands, we could deplete the necessary resources by 2050. Therefore, we require a new solution, and perovskite solar cells are emerging as a viable option to fill this gap.
Perovskite is a crystal structure composed of inorganic and organic components, named after Lev Perovski, a Russian mineral expert from the 17th and 18th centuries.
Perovskite solar cells first made their appearance in research laboratories in 2012 and caught the attention of scientists due to their remarkable ability to convert sunlight into electricity. Additionally, they offered the potential for production using a combination of inks.
Under highly controlled production conditions, where oxygen and water are completely eliminated, perovskite solar cells can now match the electricity generation efficiency of silicon cells. This represents a significant achievement.
However, the commercial manufacturing of affordable perovskite solar cells that eliminate the need for silicon is yet to be realized. What if these cells could be produced using the same printing processes employed for ordinary packaging?
Recently, my colleagues and I demonstrated that by loading a roll of plastic film into a printing press, functional perovskite solar cells can be produced. However, this process is not as simple as refilling ink in a desktop printer.
To achieve record efficiencies, scientists discovered that the semiconductor and perovskite layers in these new solar cells must be extremely thin, ranging between 50 and 500 nanometres, which is approximately 500 times smaller than a human hair.
Moreover, the inks used for printing previously required highly toxic solvents. However, after many years of dedicated effort, we have successfully formulated inks without toxic solvents that are compatible with the slot-die coating process. This process is an established industrial technique initially used for producing photographic film.
The functioning of our solar cell is as follows: The printed perovskite layer harnesses the energy from incident light and generates free electrons. The semiconductor layer then prevents the perovskite from re-absorbing these electrons, resulting in a good power conversion efficiency, which measures the ratio of optical power input to electrical power output.
One challenge that remained was how to extract the electrical charge. Previously, this was achieved by heating gold in a vacuum until it evaporated, and then depositing the vapor onto the perovskite solar cell to create electrodes.
However, we pursued a different approach by developing a carbon ink that is compatible with both the perovskite material and the slot-die coating process. The result is the production of large volumes of flexible and rollable solar cells that are capable of generating power as soon as they emerge from the printing press.
While perovskite solar cells have demonstrated high performance in research labs and have made strides in transitioning to high-volume manufacturing, there is still work to be done.
The power conversion efficiency of these rollable printed cells, currently at 10%, is useful and surpasses that of early commercial silicon panels. However, it falls short of the typical 17% conversion efficiency seen in domestic solar panels used today.
We are aware that further increases in efficiency can be achieved by leveraging higher-performing perovskite chemistry.
The engineering challenge lies in achieving high-volume, commercially produced perovskite solar panels that can match the energy generation of silicon cells. Additionally, improvements in the lifetime stability of perovskite solar cells are crucial. This can be achieved through a combination of chemistry, device design, and other strategies such as protective coatings and laminated barrier films.
In summary, the focus of research must be on translating laboratory advancements into real-world devices. The possibility of manufacturing hundreds of thousands of square meters of flexible perovskite solar cells is now one step closer to becoming a reality.
