Mar 1 2019
Scientists have discovered a new way to improve the efficiency of perovskite-type solar cells by layering different mineral forms of titanium oxide over one another. This technique improved the efficiency of these solar cells by one-sixth.
Schematic illustration the energy-level alignment between the device components with (a) FTO-AB and (b) FTO-BA as the ETLs (Image credit: Kanazawa University)
The team demonstrated that the layered titanium oxide layer can transmit electrons from the middle of the cell to its electrodes in a much better way. In the future, this innovative technique can possibly be used for developing perovskite-type solar cells, which are even more efficient.
Although a majority of solar cells are fabricated from silicon, such cells cannot be produced easily and require vacuum chambers and temperatures greater than 1000 °C. As a result, research efforts have now concentrated on a novel type of solar cell, which is based on metal halide perovskites. More efficient and low-cost solar cells can be created by economically printing perovskite solutions.
Perovskites in solar cells can convert light into electricity, but to achieve this, they have to be packed between a positive electrode and a negative electrode. However, one of these electrodes needs to be transparent so that the sun’s rays can reach the perovskites. In addition to that, any material, which is utilized to allow the flow of charges from the perovskites to the electrode, also needs to be transparent. Earlier, researchers had discovered that thin titanium oxide layers are not only transparent but can also transmit electrons to the electrode.
Now, a team of researchers from Japan and centered at Kanazawa University has performed a more comprehensive analysis of perovskite solar cells with the help of electron transport layers made of brookite and anatase. Both brookite and anatase are different mineral forms of titanium oxide. The researchers then compared the effect of utilizing either pure brookite or anatase, or combination layers (for example, brookite on top of anatase or anatase on top of brookite). The results of the study have been reported in the ACS journal, Nano Letters.
To fabricate the anatase layers, solutions were sprayed on a glass which was coated with a transparent electrode heated to 450 °C. In the meantime, the team created the brookite layers using water-soluble brookite nanoparticles, because water-soluble inks are considered to be more environmentally friendly when compared to traditional inks. Earlier, these nanoparticles have produced substandard results, but according to the researchers, that combination layers can overcome the problems previously faced when utilizing the nanoparticles.
By layering brookite on top of anatase we were able to improve solar cell efficiency by up to 16.82%.
Koji Tomita, Study Coauthor, Kanazawa University.
These latest results present new opportunities to improve perovskite solar cells, such as through the controlled manipulation and stacking of the various mineral forms of titanium oxide.
Using different mineral phases and combinations of these phases allows for better control of the electron transport out of the perovskite layer and also stops charges from recombining at the border between the perovskite material and the electron transport layer. Together, both these effects allow us to achieve higher solar cell efficiencies.
Md. Shahiduzzaman, Study First Author, Kanazawa University.
Learning how to fabricate more efficient perovskite solar cells is crucial for producing a new range of low-cost¸ printable solar cells that can deliver clean and inexpensive energy in the coming days.