328 research outputs found
Steric engineering of metal-halide perovskites with tunable optical band gaps
Owing to their high energy-conversion efficiency and inexpensive fabrication
routes, solar cells based on metal-organic halide perovskites have rapidly
gained prominence as a disruptive technology. An attractive feature of
perovskite absorbers is the possibility of tailoring their properties by
changing the elemental composition through the chemical precursors. In this
context, rational in silico design represents a powerful tool for mapping the
vast materials landscape and accelerating discovery. Here we show that the
optical band gap of metal-halide perovskites, a key design parameter for solar
cells, strongly correlates with a simple structural feature, the largest
metal-halide-metal bond angle. Using this descriptor we suggest continuous
tunability of the optical gap from the mid-infrared to the visible. Precise
band gap engineering is achieved by controlling the bond angles through the
steric size of the molecular cation. Based on these design principles we
predict novel low-gap perovskites for optimum photovoltaic efficiency, and we
demonstrate the concept of band gap modulation by synthesising and
characterising novel mixed-cation perovskites.Comment: This manuscript was submitted for publication on March 6th, 2014.
Many of the results presented in this manuscript were presented at the
International Conference on Solution processed Semiconductor Solar Cells,
held in Oxford, UK, on 10-12 September 2014. The manuscript is 37 pages long
and contains 8 figure
Prospects for Tin-Containing Halide Perovskite Photovoltaics
Tin-containing metal halide perovskites have enormous potential as photovoltaics, both in narrow band gap mixed tin–lead materials for all-perovskite tandems and for lead-free perovskites. The introduction of Sn(II), however, has significant effects on the solution chemistry, crystallization, defect states, and other material properties in halide perovskites. In this perspective, we summarize the main hurdles for tin-containing perovskites and highlight successful attempts made by the community to overcome them. We discuss important research directions for the development of these materials and propose some approaches to achieve a unified understanding of Sn incorporation. We particularly focus on the discussion of charge carrier dynamics and nonradiative losses at the interfaces between perovskite and charge extraction layers in p-i-n cells. We hope these insights will aid the community to accelerate the development of high-performance, stable single-junction tin-containing perovskite solar cells and all-perovskite tandems
Unraveling the exciton binding energy and the dielectric constant in single crystal methylammonium lead tri-iodide perovskite
We have accurately determined the exciton binding energy and reduced mass of
single crystals of methylammonium lead tri-iodide using magneto-reflectivity at
very high magnetic fields. The single crystal has excellent optical properties
with a narrow line width of meV for the excitonic transitions and a 2s
transition which is clearly visible even at zero magnetic field. The exciton
binding energy of meV in the low temperature orthorhombic phase is
almost identical to the value found in polycrystalline samples, crucially
ruling out any possibility that the exciton binding energy depends on the grain
size. In the room temperature tetragonal phase, an upper limit for the exciton
binding energy of meV is estimated from the evolution of 1s-2s
splitting at high magnetic field.Comment: 5 pages, 4 figure
Formation of thin films of organic-inorganic perovskites for high-efficiency solar cells
Organic-inorganic perovskites are currently one of the hottest topics in photovoltaic (PV) research, with power conversion efficiencies (PCEs) of cells on a laboratory scale already competing with those of established thin-film PV technologies. Most enhancements have been achieved by improving the quality of the perovskite films, suggesting that the optimization of film formation and crystallization is of paramount importance for further advances. Here, we review the various techniques for film formation and the role of the solvents and precursors in the processes. We address the role chloride ions play in film formation of mixed-halide perovskites, which is an outstanding question in the field. We highlight the material properties that are essential for high-efficiency operation of solar cells, and identify how further improved morphologies might be achieved
Vapour-Deposited Cesium Lead Iodide Perovskites: Microsecond Charge Carrier Lifetimes and Enhanced Photovoltaic Performance.
Metal halide perovskites such as methylammonium lead iodide (MAPbI3) are highly promising materials for photovoltaics. However, the relationship between the organic nature of the cation and the optoelectronic quality remains debated. In this work, we investigate the optoelectronic properties of fully inorganic vapour-deposited and spin-coated black-phase CsPbI3 thin films. Using the time-resolved microwave conductivity technique, we measure charge carrier mobilities up to 25 cm2/(V s) and impressively long charge carrier lifetimes exceeding 10 μs for vapour-deposited CsPbI3, while the carrier lifetime reaches less than 0.2 μs in the spin-coated samples. Finally, we show that these improved lifetimes result in enhanced device performance with power conversion efficiencies close to 9%. Altogether, these results suggest that the charge carrier mobility and recombination lifetime are mainly dictated by the inorganic framework rather than the organic nature of the cation
- …