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Perovskite nanowires promise better lasers
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Nano Today (2015) xxx, xxx—xxx
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/nanotoday
NEWS AND OPINIONS
Perovskite nanowires promise better lasers Cordelia Sealy
Lead halide perovskites, which promise a new generation of highly efficient solar cells, can now be grown in the form nanowires to make lasers too. Researchers from the University of Wisconsin-Madison and Columbia University have developed a simple solution-based synthesis route for producing high quality, single crystal nanowires of methyl ammonium lead halide perovskite (CH3 NH3 PbX3 , X = I, Br, Cl) that make promising lasers [H. Zhu et al., Nature Materials (2015), http://dx.doi.org/10.1038/nmat4271]. The key to the process is the slow release of Pb precursor (PbI4 2− ) from a thin solid film of lead acetate (PbAc2 ), which is deposited onto a glass plate and submerged in an organic solution of the other reactant, a methylammonium halide of I, Br, or Cl. After 24 h, rectangular nanowires of CH3 NH3 PbI3 a few hundred nanometers wide and up to ∼20 m long with flat end facets are formed on the surface (Fig. 1). ‘‘There’s no heat, no vacuum, no special equipment needed,’’ says Song Jin of the University of WisconsinMadison who, jointly with Xiaoyang Zhu at Columbia, led the collaboration. ‘‘The single-crystal perovskite nanowires. . . are high quality, almost free of defects, and have the reflective parallel facets that a laser needs.’’ For lasing, the researchers transferred the nanowires onto Si/SiO2 substrates via a simple dry contact process. The perovskite nanowires show exceptional lasing characteristics upon optical pumping, including a lasing threshold of ∼220—600 nJ cm−2 at room temperature and a quality factor, Q, of ∼3600 — more than an order of magnitude higher than state-of-the-art GaAs—AlGaAs core—shell nanowire lasers operating at 4 K. Remarkably, the perovskite nanowires show a quantum yield of 87%, which the researchers believe could reach unity (100%). The low lasing threshold and high Q factor — the best reported so far for nanowire lasers — can be attributed to the
E-mail address: [email protected]
Figure 1 Optical microscopy image of as-synthesized, rectangular CH3 NH3 PbI3 nanowires. Credit: Song Jin.
long carrier lifetimes and low nonradiative recombination rate in perovskites, say the researchers. As well as extreme efficiency, a major advantage of nanowire lasers is that the emitted wavelength (i.e. lasing color) can be readily tuned by adjusting the chemistry of the perovskite. The researchers used Br to create green emission, but also mixed different amounts of iodide, bromide, and chloride in the precursor solution to tune emission from the near-infrared to visible range. ‘‘These are simply the best nanowire lasers by all performance criteria,’’ says Jin, ‘‘even when compared to materials grown in high temperature and high vacuum. Perovskites are intrinsically good materials for lasing, but when they are grown into high-quality crystals with the proper size and shape, they really shine.’’ The nanowires appear to be fairy robust and amenable to post-processing thanks to their rectangular shape. Although
1748-0132/$ — see front matter http://dx.doi.org/10.1016/j.nantod.2015.04.007 NANTOD-446; No. of Pages 2
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2 lasing stability degrades over a few tens of minutes, the researchers believe this can be improved upon with changes to the structure and better heat dissipation. ‘‘Before these nanowire lasers can be used in practical applications, their chemical stability must be improved,’’ cautions Jin. ‘‘Also important is finding a way to stimulate the laser with electricity rather than light.’’ Although Daniël Vanmaekelbergh of Utrecht University in the Netherlands agrees that the chemical and
C. Sealy thermal stability of perovskites could be a challenge for lasing applications, he believes there is a bright future for perovskite-based optoelectronics. ‘‘The practical impact of the findings reported could become very important,’’ he told Nano Today. ‘‘[Not least] of all, these perovskite nanowire lasers are fabricated with low-temperature solution chemistry, unlike hightemperature gas-phase fabrication ZnO and GaN nanowire lasers.’’
ARTICLE IN PRESS
Nano Today (2015) xxx, xxx—xxx
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/nanotoday
NEWS AND OPINIONS
Perovskite nanowires promise better lasers Cordelia Sealy
Lead halide perovskites, which promise a new generation of highly efficient solar cells, can now be grown in the form nanowires to make lasers too. Researchers from the University of Wisconsin-Madison and Columbia University have developed a simple solution-based synthesis route for producing high quality, single crystal nanowires of methyl ammonium lead halide perovskite (CH3 NH3 PbX3 , X = I, Br, Cl) that make promising lasers [H. Zhu et al., Nature Materials (2015), http://dx.doi.org/10.1038/nmat4271]. The key to the process is the slow release of Pb precursor (PbI4 2− ) from a thin solid film of lead acetate (PbAc2 ), which is deposited onto a glass plate and submerged in an organic solution of the other reactant, a methylammonium halide of I, Br, or Cl. After 24 h, rectangular nanowires of CH3 NH3 PbI3 a few hundred nanometers wide and up to ∼20 m long with flat end facets are formed on the surface (Fig. 1). ‘‘There’s no heat, no vacuum, no special equipment needed,’’ says Song Jin of the University of WisconsinMadison who, jointly with Xiaoyang Zhu at Columbia, led the collaboration. ‘‘The single-crystal perovskite nanowires. . . are high quality, almost free of defects, and have the reflective parallel facets that a laser needs.’’ For lasing, the researchers transferred the nanowires onto Si/SiO2 substrates via a simple dry contact process. The perovskite nanowires show exceptional lasing characteristics upon optical pumping, including a lasing threshold of ∼220—600 nJ cm−2 at room temperature and a quality factor, Q, of ∼3600 — more than an order of magnitude higher than state-of-the-art GaAs—AlGaAs core—shell nanowire lasers operating at 4 K. Remarkably, the perovskite nanowires show a quantum yield of 87%, which the researchers believe could reach unity (100%). The low lasing threshold and high Q factor — the best reported so far for nanowire lasers — can be attributed to the
E-mail address: [email protected]
Figure 1 Optical microscopy image of as-synthesized, rectangular CH3 NH3 PbI3 nanowires. Credit: Song Jin.
long carrier lifetimes and low nonradiative recombination rate in perovskites, say the researchers. As well as extreme efficiency, a major advantage of nanowire lasers is that the emitted wavelength (i.e. lasing color) can be readily tuned by adjusting the chemistry of the perovskite. The researchers used Br to create green emission, but also mixed different amounts of iodide, bromide, and chloride in the precursor solution to tune emission from the near-infrared to visible range. ‘‘These are simply the best nanowire lasers by all performance criteria,’’ says Jin, ‘‘even when compared to materials grown in high temperature and high vacuum. Perovskites are intrinsically good materials for lasing, but when they are grown into high-quality crystals with the proper size and shape, they really shine.’’ The nanowires appear to be fairy robust and amenable to post-processing thanks to their rectangular shape. Although
1748-0132/$ — see front matter http://dx.doi.org/10.1016/j.nantod.2015.04.007 NANTOD-446; No. of Pages 2
+Model
ARTICLE IN PRESS
2 lasing stability degrades over a few tens of minutes, the researchers believe this can be improved upon with changes to the structure and better heat dissipation. ‘‘Before these nanowire lasers can be used in practical applications, their chemical stability must be improved,’’ cautions Jin. ‘‘Also important is finding a way to stimulate the laser with electricity rather than light.’’ Although Daniël Vanmaekelbergh of Utrecht University in the Netherlands agrees that the chemical and
C. Sealy thermal stability of perovskites could be a challenge for lasing applications, he believes there is a bright future for perovskite-based optoelectronics. ‘‘The practical impact of the findings reported could become very important,’’ he told Nano Today. ‘‘[Not least] of all, these perovskite nanowire lasers are fabricated with low-temperature solution chemistry, unlike hightemperature gas-phase fabrication ZnO and GaN nanowire lasers.’’