Research highlights: Perovskites
- PDF / 1,061,255 Bytes
- 2 Pages / 585 x 783 pts Page_size
- 22 Downloads / 180 Views
RESEARCH HIGHLIGHTS :
Perovskites
By Prachi Patel Feature Editor: Pabitra K. Nayak
Research on perovskites has progressed rapidly, with solar-cell efficiencies now at 22.7%, five times higher than those of the first cells reported in 2009. MRS Bulletin presents the impact of a selection of recent advances in this burgeoning field.
A
dding potassium to perovskite films can increase the efficiency of solar cells, shows new research published inNature (doi:10.1038/nature25989). Perovskite solar cells suffer from nonradiative losses: the recombination of light-generated charge carriers without generating a photon, when carriers get trapped at crystal defects. Efficiency increases when more carriers recombine radiatively, producing a photon that can again generate charge carriers. Another challenge is the movement of ions in the material, which creates spatial distribution of bandgaps and reduces the solarcell performance. An international team of researchers led by Samuel Stranks at the University of Cambridge added potassium iodide to a precursor solution for a cesiumformamidinium-methylammonium lead halide perovskite thin film. The potassium iodide forms a layer on the
T
he presence of lead in high-performance perovskites raises serious concern. Unfortunately, lead-free perovskites based on tin halide compounds have come up short in terms of efficiency and stability. A new type of three-dimensional (3D) hollow perovskite might be the answer, say Northwestern University researchers. Mercouri Kanatzidis and his colleagues first reported the hollow hybrid halide perovskites in 2017. They have now used a suite of physical and
Atomic-scale view of perovskite crystal formation with added potassium. Credit: Matthew Klug (University of Oxford).
surface and at the grain boundaries of the perovskite, healing the traps and preventing ions from moving. The films had a very high luminescence yield—important to maximize
efficiency—exceeding 95%, as well as excellent charge transport, with mobilities of more than 40 cm2/V∙s. Solar cells made with the films had an efficiency of 21.5%.
spectroscopic methods to study the material’s chemical nature and structural properties. Their analysis appears in the Journal of the American Chemical Society (doi:10.1021/jacs.8b01034). Hollow perovskites incorporate the ethylenediammonium (en) cation into 3D ASnX3 perovskites. Using a range of techniques such as x-ray diffraction, H-NMR (hydrogen-1 nuclear magnetic resonance), and gas pycnometry, researchers confirmed that the en cation creates large vacancies in the metal-halide
framework. Density functional theory calculations showed that this disruption leads to a widening of the material’s bandgap, which is important for tandem solar cells in which perovskites sit atop silicon cells. The en cation also makes the material more stable in air and improves its photoelectric properties. Hollow perovskites present “a new platform of highly promising light absorbers that can be utilized in single junction or tandem solar cells,” the authors
Data Loading...
