Metal halide perovskites are generating enormous interest for their use in solar cells and light-emission applications. One property linking the high performance of these devices is a high radiative ...efficiency of the materials; indeed, a prerequisite for these devices to reach their theoretical efficiency limits is the elimination of all nonradiative decay. Despite remarkable progress, there exists substantial parasitic nonradiative recombination in thin films of the materials and when interfaced into devices, and the origin of these processes is still poorly understood. In this Perspective, I will highlight key observations of these parasitic pathways on both the macro- and microscale in thin films and full devices. I will summarize our current understanding of the origin of nonradiative decay, as well as existing solutions that hint at facile ways to remove these processes. I will also show how these nonradiative decay pathways are intimately related to ionic migration, leading to the tantalizing conclusion that eliminating one phenomenon could in turn remove the other, ultimately pushing devices to their theoretical limits.
Metal-halide perovskites are crystalline materials originally developed out of scientific curiosity. Unexpectedly, solar cells incorporating these perovskites are rapidly emerging as serious ...contenders to rival the leading photovoltaic technologies. Power conversion efficiencies have jumped from 3% to over 20% in just four years of academic research. Here, we review the rapid progress in perovskite solar cells, as well as their promising use in light-emitting devices. In particular, we describe the broad tunability and fabrication methods of these materials, the current understanding of the operation of state-of-the-art solar cells and we highlight the properties that have delivered light-emitting diodes and lasers. We discuss key thermal and operational stability challenges facing perovskites, and give an outlook of future research avenues that might bring perovskite technology to commercialization.
The influence of the Rashba effect Stranks, Samuel D; Plochocka, Paulina
Nature materials,
05/2018, Letnik:
17, Številka:
5
Journal Article
Recenzirano
Heavy atoms and crystal or inversion symmetry breaking may promote Rashba effects in halide perovskites. Sam Stranks and Paulina Plochocka propose experiments to assess the existence of these effects ...and their implications on the photophysics of perovskites.
Solar cells based on the organicinorganic tri-halide perovskite family of materials have shown signicant progress recently, oering the prospect of low-cost solar energy from devices that are very ...simple to process. Fundamental to understanding the operation of these devices is the exciton binding energy, which has proved both dicult to measure directly and controversial
Colloidal perovskite nanoplatelets are a promising class of semiconductor nanomaterialsexhibiting bright luminescence, tunable and spectrally narrow absorption and emission features, strongly ...confined excitonic states, and facile colloidal synthesis. Here, we demonstrate the high degree of spectral tunability achievable through variation of the cation, metal, and halide composition as well as nanoplatelet thickness. We synthesize nanoplatelets of the form L2ABX3 n−1BX4, where L is an organic ligand (octylammonium, butylammonium), A is a monovalent metal or organic molecular cation (cesium, methylammonium, formamidinium), B is a divalent metal cation (lead, tin), X is a halide anion (chloride, bromide, iodide), and n–1 is the number of unit cells in thickness. We show that variation of n, B, and X leads to large changes in the absorption and emission energy, while variation of the A cation leads to only subtle changes but can significantly impact the nanoplatelet stability and photoluminescence quantum yield (with values over 20%). Furthermore, mixed halide nanoplatelets exhibit continuous spectral tunability over a 1.5 eV spectral range, from 2.2 to 3.7 eV. The nanoplatelets have relatively large lateral dimensions (100 nm to 1 μm), which promote self-assembly into stacked superlattice structuresthe periodicity of which can be adjusted based on the nanoplatelet surface ligand length. These results demonstrate the versatility of colloidal perovskite nanoplatelets as a material platform, with tunability extending from the deep-UV, across the visible, into the near-IR. In particular, the tin-containing nanoplatelets represent a significant addition to the small but increasingly important family of lead- and cadmium-free colloidal semiconductors.
Light emission is a critical property that must be maximized and controlled to reach the performance limits in optoelectronic devices such as photovoltaic solar cells and light‐emitting diodes. ...Halide perovskites are an exciting family of materials for these applications owing to uniquely promising attributes that favor strong luminescence in device structures. Herein, the current understanding of the physics of light emission in state‐of‐the‐art metal‐halide perovskite devices is presented. Photon generation and management, and how these can be further exploited in device structures, are discussed. Key processes involved in photoluminescence and electroluminescence in devices as well as recent efforts to reduce nonradiative losses in neat films and interfaces are discussed. Finally, pathways toward reaching device efficiency limits and how the unique properties of perovskites provide a tremendous opportunity to significantly disrupt both the power generation and lighting industries are outlined.
Lead‐halide perovskites have demo‐nstrated rapid rises in optoelectronic device performance, which directly links to their efficient luminescence properties. The current understanding of the physics of light emission in perovskites is discussed, along with current outstanding challenges and opportunities to push device performances beyond existing technologies.
Riding on the coat tails of rapid developments in single‐junction halide perovskite solar cells, all‐perovskite multijunction solar cells have recently garnered significant attention, with the ...highest power‐conversion efficiency already reaching 25.6%. Much of this progress has been fueled by the rapid rise in the photovoltaic performance of low‐bandgap halide perovskite absorbers, materials, which, to date, have only been achievable by the partial or complete substitution of lead with tin. However, much room still exists to develop a more critical understanding of key material properties in these low‐bandgap perovskites. Herein, the key optoelectronic properties of absorption, carrier generation, recombination, and transport in these tin‐containing perovskites are discussed, showing that intrinsic doping distinctively impacts many of these properties, thereby rendering this class of halide perovskites unique within the family. Current understanding of the mechanisms that degrade optoelectronic performance in these materials and the corresponding devices are also summarized. These collective results highlight an important interplay between doping, defects, and degradation that will need to be controlled. Finally, the current gaps in understanding of these low‐bandgap perovskites are outlined, thereby providing guidelines for further research, which will unlock their full potential for realizing a plethora of high‐performance optoelectronic devices.
Low‐bandgap tin‐containing halide perovskites have recently demonstrated impressive photovoltaic performances owing to their unique optoelectronic properties, which are yet to be fully explored. A perspective on the absorption, carrier generation, recombination, and transport phenomena in these materials is provided, underscoring an interesting interplay between doping, defects, and degradation that needs to be controlled for future optoelectronic applications.
In spite of the unprecedented advances of organohalide lead perovskites in optoelectronic devices, many of the characteristics of this class of materials remain poorly understood. Several ...experimental hints point to defect migration as a plausible mechanism underlying such anomalous properties. Here we present an experimental and theoretical investigation combining measurements of PL rise dynamics at varying temperatures with first principles computational modeling of defect migration under light irradiation. We propose a model in which light irradiation promotes the annihilation of VI+/Ii- Frenkel pairs, which we show to be relatively abundant in polycrystalline MAPbI3. This partly restores a non-defective crystalline environment and eliminates the trapping centers associated with such defect pairs. The PL rise time dynamics at varying temperature provide an activation energy consistent with that calculated for migration of iodine defects, supporting the proposed model. We further illustrate a synergistic effect of ion/defect migration and lattice dynamics, with local reorientation of the methylammonium cations assisting the migration of charged defects. Our results provide the interpretative basis for further investigating the unusual light-induced modifications characterizing organohalide perovskites.
Lead halide perovskites are mixed electron–ion conductors that support high rates of solid-state ion transport at room temperature, in addition to conventional electron and hole conduction. Mass ...transport mediated by charged defects is responsible for unusual phenomena such as current–voltage hysteresis in photovoltaic devices, anomalous above-bandgap photovoltages, light-induced lattice expansion and phase separation, self-healing, and rapid chemical conversion between halides. We outline the principles that govern ion transport in perovskite solar cells including intrinsic (point and extended defects) and extrinsic (light, heat, electrical fields, and chemical gradients) factors. These microscopic processes underpin a wide range of reported observations, including photoionic conductivity, and offer valuable directions for both limiting ion transport, where required, and harnessing it to enable new functionality.
It is common practice in the lead halide perovskite solar cell field to add a small molar excess of lead iodide (PbI2) to the precursor solution to increase the device performance. However, recent ...reports have shown that an excess of PbI2 can accelerate performance loss. In addition, PbI2 is photoactive (band gap ∼2.3 eV), which may lead to parasitic absorption losses in a solar cell. Here we show that devices using small quantities of excess PbI2 exhibit better device performance as compared with stoichiometric devices, both initially and for the duration of a stability test under operating conditions, primarily by enhancing the charge extraction. However, the photolysis of PbI2 negates the beneficial effect on charge extraction by leaving voids in the perovskite film and introduces trap states that are detrimental for device performance. We propose that although excess PbI2 provides a good template for enhanced performance, the community must continue to seek other additives or synthesis routes that fulfill the same beneficial role as excess PbI2, but without the photolysis that negates these beneficial effects under long-term device operation.
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