Nanoscale & Nanoscale Advances joint themed collection on halide perovskite nanocrystals

Lakshminarayana Polavarapu

Lakshminarayana Polavarapu is a group leader in the Chair for Photonics and Optoelectronics at the newly formed Nanoinstitute Munich of Ludwig-Maximilians-University in Munich, Germany. He obtained an MSc in Chemistry from the University of Hyderabad (India) in 2005 and his PhD in Physical Chemistry from the National University of Singapore in 2011. After being a postdoctoral fellow at CIC biomaGUNE and University of Vigo (Spain), he joined the Chair for Photonics and Optoelectronics at the Ludwig-Maximilians-University of Munich as an Alexander von Humboldt postdoctoral fellow. His current research interests include shape-controlled synthesis, self-assembly and optical spectroscopy of colloidal perovskite nanocrystals.

Qiao Zhang

Qiao Zhang is a professor in the Institute of Functional Nano & Soft Materials, Soochow University, China. He received his PhD from the Department of Chemistry, University of California, Riverside, in 2012 under the supervision of Prof. Yadong Yin. After being a postdoctoral fellow in the Department of Chemistry, University of California Berkeley (with Prof. A. Paul Alivisatos and Prof. Gabor A. Somorjai), he joined Soochow University in 2014 as a professor. His main research areas are molecular level studies of surface and heterogeneous catalysis, and controllable synthesis of all-inorganic perovskites with tunable optical properties and their applications.

Roman Krahne

Roman Krahne is the leader of the Optoelectronics Group at the Italian Institute of Technology (IIT) in Genoa. He graduated in physics and obtained his PhD from the University of Hamburg (Germany) in 2000, and then was at the Weizmann Institute of Science (Israel) as a postdoctoral fellow for two years, working on electronic properties of single molecules. In 2003, he joined the National Nanotechnology Lab in Italy, and in 2009 he became senior researcher at the IIT headquarters in Genoa. His research interests are centered on optical and electrical properties of colloidal nanomaterials, plasmonic nanostructures, and metamaterials.

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Colloidal semiconductor nanocrystals (NCs), also known as colloidal quantum dots (QDs) have played an indispensable role in the development of modern nanoscience and nanotechnology because of their unique optical and electronic properties, and they are still being intensively investigated for various potential applications. Semiconductor NCs offer significant advantages over conventional organic fluorescent dyes, including the tunability of emission color by their size and composition, excellent color purity, ease of preparation and controllable surface chemistry enabling their dispersion in various solvents for solution processability. As a consequence, the past two decades have witnessed tremendous progress in the shape-controlled synthesis, self-assembly, surface functionalization and optoelectronic device applications of II–VI and III–V semiconductor QDs.

Recently, metal halide perovskites have emerged as a new class of semiconductor material with extraordinary optical and electronic properties. Perovskite materials of the form APbX₃ (with A as the inorganic or organic cation, and X = Cl, Br, or I) have been well known since the late 1970s from the work by Weber.¹ They became popular after the first report on halide perovskite solar cells in 2009 by Kojima et al.² Since then, halide perovskites have created large excitement in the photovoltaic research community that was stimulated by a meteoric rise in the power conversion efficiency of perovskite solar cells from 3.8% to over 22% in a short development time. In addition, the outstanding optical properties of perovskites have made them excellent light sources for applications in LEDs, photodetectors, photo transistors and lasers. The early studies on perovskites were focused on the optimization of bulk films for device applications. Despite the rapid progress in perovskite materials in photovoltaics and optoelectronics, the properties that make them so special, like their tolerance to defects, are yet to be fully understood.

From the II–VI and III–V semiconductor materials, we know that colloidal nanocrystals offer several advantages over their bulk counterparts, including solution processability, enhanced photoluminescence efficiency and tunable emission through quantum confinement effects. The first solution phase colloidal synthesis of organic–inorganic hybrid perovskite NCs was published in 2014 by Pérez-Prieto et al.³ A year later, Kovalenko et al.⁴ reported the colloidal synthesis of all-inorganic perovskite NCs. Since then, metal halide perovskite NCs have received significant research interest due to their extraordinary optical properties as well as their appeal as emitters in efficient light sources.

The unique feature of perovskite NCs is that they exhibit near unity photoluminescence quantum yield (PLQY) without the need of a core–shell architecture, unlike the conventional QDs (e.g. CdSe/CdS/ZnS and CdSe/ZnSe/ZnS core-multi shell NCs). The emission color of perovskite NCs is easily tunable across the visible spectrum by the halide composition and by confinement effects. Like in conventional colloidal systems, ligands play a crucial role in the shape and size control of perovskite NCs, and also in the passivation of surface defects, which is decisive for high PLQY.⁵ In the last few years, we have witnessed extremely rapid progress in the synthesis of perovskite NCs of a wide range of morphologies and shapes, such as quantum dots, nanocubes, nanowires, nanorods, nanoplatelets, and nanosheets. In fact, it is possible to control the dimensions of NCs with monolayer precision, which leads to strong tunability of the band gap in nanowires, nanoplatelets and nanosheets.^6,7 Introducing organic molecules as spacer layers in between the octahedral planes enabled the fabrication of layered perovskites with a large band gap and emission at a wavelength of around 400 nm, which can be tuned by the number of stacked octahedral layers.^8,9 Similar to van der Waals crystals, flakes with only a few octahedral layers can be obtained via liquid phase or Scotch tape exfoliation. In addition, post-synthetic strategies have been developed to control the composition, morphology, crystal structure and surface defects.^10,11 Despite the great success of lead halide perovskites, the toxicity of lead (Pb) is a major concern for advancing the field toward commercial applications. This stimulated a significant effort in the replacement of Pb with other nontoxic metals via direct synthesis or through post-synthetic cation exchange.^12,13 There has also been great progress in the enhancement of PLQY and stability through doping with metal ions such as Mn²⁺, Cu²⁺, Cd²⁺ and lanthanides. Research on applications of perovskite NCs, especially in LEDs, lasers, and photodetectors, has in turn improved their synthesis, leading to more stable optoelectronic properties and upscaled fabrication pathways.^14–16 The fruitful interaction between the development of novel metal halide perovskite materials and the optimization of the existing ones for improved device performance is strongly driving this field and opens a bright future for a wide range of optical and optoelectronic applications. Therefore, the number of both researchers working and publications on perovskite NCs has increased exponentially over the last few years, with more than 800 papers published in 2018 that involve perovskite nanocrystals.

This themed online collection of Nanoscale and Nanoscale Advances aims at providing a platform for recent developments in the expanding field of metal halide perovskite NCs, including shape and composition-controlled synthesis (DOI: 10.1039/C8NR09349K), thin film morphologies (DOI: 10.1039/C8NR09853K), 2D layered materials (DOI: 10.1039/C9NR00638A), replacement of Pb (DOI: 10.1039/C9NR01031A), post-synthetic metal ion doping (DOI: 10.1039/C8NR09845J), single particle studies (DOI: 10.1039/C8NR10110H), and applications in LEDs (DOI: 10.1039/C8NR09885A), flexible photodetectors (DOI: 10.1039/C8NR08026G), nanorotors (DOI: 10.1039/C8NR06768F), and lasing (DOI: 10.1039/C8NR09856E).

Read the full collection online here.

As guest editors of this themed collection, we thank all of the authors for their high quality contributions, and hope that researchers from various fields will enjoy reading the collection. We thank Sara E. Skrabalak, Hannah Kerr, and the editorial staff of Nanoscale and Nanoscale Advances for their kind support.

References

1. D. Weber, Z. Naturforsch., B, 1978, 33, 1443.
2. A. Kojima, K. Teshima, Y. Shirai and T. Miyasaka, J. Am. Chem. Soc., 2009, 131, 6050.
3. L. C. Schmidt, A. Pertegás, S. González-Carrero, O. Malinkiewicz, S. Agouram, G. Mínguez Espallargas, H. J. Bolink, R. E. Galian and J. Pérez-Prieto, J. Am. Chem. Soc., 2014, 136, 850.
4. L. Protesescu, S. Yakunin, M. Bodnarchuk, F. Krieg, R. Caputo, C. Hendon, R. Yang, A. Walsh and M. Kovalenko, Nano Lett., 2015, 15, 3692.
5. B. J. Bohn, Y. Tong, M. Gramlich, M. L. Lai, M. Döblinger, K. Wang, R. L. Z. Hoye, P. Müller-Buschbaum, S. D. Stranks, A. S. Urban, L. Polavarapu and J. Feldmann, Nano Lett., 2018, 18, 5231–5238.
6. D. Yang, M. Cao, Q. Zhong, P. Li, X. Zhang and Q. Zhang, J. Mater. Chem. C, 2019, 7, 757–789.
7. J. Shamsi, Z. Dang, P. Bianchini, C. Canale, F. D. Stasio, R. Brescia, M. Prato and L. Manna, J. Am. Chem. Soc., 2016, 138, 7240–7243.
8. C. C. Stoumpos, D. H. Cao, D. J. Clark, J. Young, J. M. Rondinelli, J. I. Jang, J. T. Hupp and M. G. Kanatzidis, Chem. Mater., 2016, 28, 2852–2867.
9. A. Castelli, G. Biffi, L. Ceseracciu, D. Spirito, M. Prato, D. Altamura, C. Giannini, S. Artyukhin, R. Krahne, L. Manna and M. P. Arciniegas, Adv. Mater., 2019, 31, 1805608.
10. Q. A. Akkerman, V. D'Innocenzo, S. Accornero, A. Scarpellini, A. Petrozza, M. Prato and L. Manna, J. Am. Chem. Soc., 2015, 137, 10276–10281.
11. W. J. Mir, A. Swarnkar and A. Nag, Nanoscale, 2019, 11, 4278–4286.
12. T. C. Jellicoe, J. M. Richter, H. F. Glass, M. Tabachnyk, R. Brady, S. E. Dutton, A. Rao, R. H. Friend, D. Credgington, N. C. Greenham and M. L. Bohm, J. Am. Chem. Soc., 2016, 138, 2941–2944.
13. S. E. Creutz, E. N. Crites, M. C. D. Siena and D. R. Gamelin, Nano Lett., 2018, 18, 1118–1123.
14. J. Shamsi, P. Rastogi, V. Caligiuri, A. L. Abdelhady, D. Spirito, L. Manna and R. Krahne, ACS Nano, 2017, 11, 10206–10213.
15. Y. Tong, E.-P. Yao, A. Manzi, E. Bladt, K. Wang, M. Döblinger, S. Bals, P. Müller-Buschbaum, A. S. Urban, L. Polavarapu and J. Feldmann, Adv. Mater., 2018, 30, 1801117.
16. Q. Zhong, M. Cao, H. Hu, D. Yang, M. Chen, P. Li, L. Wu and Q. Zhang, ACS Nano, 2018, 12, 8579–8587.

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