Disorderly composed perovskite enables more efficient solar cells
Scientists from the University of Cambridge, among others, argue that perovskites can be more efficient if their chemical composition is not properly ordered. This can not only result in better solar panels, but also simplify the production process of perovskites.
According to the researchers, the discovery that making the materials less orderly had a positive effect, was completely unexpected. “It was fascinating to see how much light we could get from these materials in a scenario where we expected them to be quite dark,” said one researcher.
Their surprise stems from the fact that it works the other way around with crystallized silicon, which is still the most commonly used material for the production of solar panels. Achieving the best energy conversion with silicon crystals requires an expensive and time-consuming process in which the silicon atoms must be placed in a very orderly and symmetrical structure. Unevenness, dust and dirt are undesirable, otherwise the charged particles can get stuck, as it were, after absorbing the photons and the energy is lost. As a result, the material must be made in a clean room.
Perovskites are alternatives to silicon and can consist of all kinds of minerals. They are soft, malleable, artificial crystals that can convert sunlight into electricity. They absorb a lot of light, can transport electrons well and are cheap to make. Solar cells based on perovskites, like the silicon-based cells, achieve an efficiency of about 25 percent, but until now it was unknown why these relatively roughly processed perovskites work so well.
According to the researchers, their raw, multi-layered, mixed materials lead to higher efficiency, because there are many spots with different chemical compositions. That would more or less catch the charges. Researcher Sascha Feldmann says that in this way mountains and valleys are created in energy, in which the charge can be concentrated. According to him, this makes it easier to remove them from the solar cell and it would be more efficient to produce light from these ‘hot spots’ in an LED.
According to Feldmann, perovskites are the new class of semiconductors that can lead to a revolution in all kinds of devices. Very efficient emission occurs when the charged particles are dislodged by exposing them to energy sources such as light or a voltage in an LED. Until now, attempts were made to make the films more homogeneous during manufacture, but according to Feldmann, based on the research, a simple inkjet printing process can already lead to better results.
Incidentally, it is still a challenge to find the right manufacturing conditions for the creation of the optimal imbalance in the materials, so that maximum efficiency is achieved. Perovskites are sensitive to moisture, so something has to be found on that as well. For now, some work is also needed before this research results in solar panels based on these materials that are just as sustainable as panels with silicon. Incidentally, Maria Loi, professor of photophysics and optoelectronics at the University of Groningen, tells NRC that further research has yet to show whether the efficiency of the perovskite is actually due to the messy structure or whether it is due to the composition of the material.
The research is published in the scientific journal Nature Photonics, under the title Photodoping through local charge carrier accumulation in alloyed hybrid perovskites for highly efficient luminescence.