EPFL is a Switzerland-based technical university and research center. EPFL is focuses on three missions: teaching, research and technology transfer. EPFL works together with an extensive network of partners including other universities and institutes of technology, secondary schools and colleges, industry and economy, political circles and the general public.
EPFL does extensive perovskite R&D work and is responsible for many publications and advancements in the field.
The latest EPFL perovskite news:
EPFL and AMI teams develop a method to replace one of the least stable components in perovskite solar cells
Researchers at the Adolphe Merkle Institute in Fribourg and the Ecole Polytechnique Fédérale de Lausanne have developed a new technique to replace one of the least stable components in perovskite solar cells, which could be a major step towards commercialization.
Perovskites are seen as promising thin-film solar-cell materials because they can absorb light over a broad range of solar spectrum wavelengths thanks to their tuneable bandgaps. Charge carriers (electrons and holes) can also diffuse through them quickly and over long lengths. The most efficient perovskite solar cells usually contain bromide and MA, which is thermally unstable. To overcome this problem, researchers tried replace MA with FA since it is not only more thermally stable but also has an optimal redshifted bandgap. Unfortunately, because of its large size, FA does distort the perovskite lattice and tends to produce a photoinactive “yellow” phase at room temperature. The other photoactive “black phase” can only be seen at high temperatures. However, the researchers in this new work have now found a way to stabilize the black phase of FA at room temperature.
Researchers from Qatar, Switzerland and Italy have designed a composite perovskite material with a thin surface layer that repels water and protects against moisture-induced degradation. The team has managed to do this by allowing the self-assembly of two-dimensional perovskite on top of a three-dimensional perovskite in an inert atmosphere.
The composite perovskite did not decompose when kept in highly humid air for three days. The top layer of the 2D perovskite blocked water penetration into the 3D perovskite beneath it, preventing its degradation. Bare 3D perovskite completely degrades at a similar humidity.
EPFL the CSEM PV-center researchers have combined silicon and perovskite to create solar cells with the resulting efficiency of 25.2%, in what is regarded as a record for this type of tandem cell. Their innovative yet simple manufacturing technique could be directly integrated into existing production lines, and efficiency could eventually rise above 30%.
The researchers explain that creating an effective tandem structure by superposing two materials is no easy task. "Silicon's surface consists of a series of pyramids measuring around 5 microns, which trap light and prevent it from being reflected. However, the surface texture makes it hard to deposit a homogeneous film of perovskite," explains Quentin Jeangros, who co-authored the paper. A common problem in such cells arises from the fact that when the perovskite is deposited in liquid form, it accumulates in the valleys between the pyramids while leaving the peaks uncovered, leading to short circuits. The team tackled this problem by using evaporation methods to form an inorganic base layer that fully covers the pyramids. That layer is porous, enabling it to retain the liquid organic solution that is then added using a thin-film deposition technique called spin-coating. The researchers subsequently heat the substrate to a relatively low temperature of 150°C to crystallize a homogeneous film of perovskite on top of the silicon pyramids.
Researchers from the Institute of Physical Chemistry of the Polish Academy of Sciences and the Faculty of Chemistry of Warsaw University of Technology have designed what they consider to be an improved version of a perovskite, containing in the crystal structure a relatively large organic ion, a guanidinium cation. Lab tests at the EPFL have reportedly shown that photovoltaic cells made of the new perovskite work more efficiently than the cells prepared using its original form.
The guanidinium cation was incorporated into the crystal structure of the classic perovskite using a ‘solvent-less’ mechanochemical approach. The experiments proved that from many aspects the new, modified perovskites are clearly better than the parent (CH3NH3)PbI3.
A study by EPFL researchers Michael Grätzel and Amita Ummadisingu offers valuable insight into the sequential deposition reaction. This process, used as one of the main methods for depositing perovskite films onto panel structures, was developed in 2013 by Michael Grätzel and co-workers at EPFL. Many studies have since tried to control this process with additives, compositional changes, and temperature effects, but none of these has provided a complete understanding of the entire sequential deposition reaction. This prevents adequate control over film quality, which determines the performance of the solar cell.
The EPFL scientists began with X-ray diffraction analysis and scanning electron microscopy to study in depth the crystallization of lead iodide (PbI2), which is the first stage of the reaction. They then used, for the first time, SEM-cathodoluminescence imaging to study the nano-scale dynamics of perovskite film formation.