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Halide perovskite quantum dots: potential candidates for display technology
Sci. Bull. (2015) 60(18):1622–1624 DOI 10.1007/s11434-015-0884-y
www.scibull.com www.springer.com/scp
Research Highlight
Halide perovskite quantum dots: potential candidates for display technology Zelong Bai • Haizheng Zhong
Published online: 18 September 2015 Ó Science China Press and Springer-Verlag Berlin Heidelberg 2015
Motivated by the color tunability and narrow-band emission peak of colloidal quantum dots (QDs), the concepts of quantum dot light-emitting diodes (QD-LEDs), based on either the photoluminescence (PL) or electroluminescence (EL) mechanism, have been proposed for a few years [1]. Using QD-LEDs in the backlighting system of liquid crystal display (LCD) can significantly expand the color gamut of display and present vibrant colored images. However, even though CdSe-based QDs have been commercially used in backlighting system, this innovative technique is still suffering from the complicated preparation process, the lack of surface control during process, and unacceptable price of high-quality CdSe-based QDs. Moreover, the developing of high-performance (bright, efficient, and stable) EL devices strongly relies on the precise band engineering of the core and shell as well as surface ligands [2]. To solve these problems, alternative materials with simple process have been much aspired. Halide perovskites exhibit wide wavelength tunability (400–800 nm), narrow-band emission (full width at half maximum, FWHM *20 nm), which make them to be potential candidates for light-emitting applications and have been investigated for at least 20 years. However, their use in light-emitting diodes suffer from the limited photoluminescence quantum yields (PLQYs) at low excitation
Electronic supplementary material The online version of this article (doi:10.1007/s11434-015-0884-y) contains supplementary material, which is available to authorized users. Z. Bai H. Zhong (&) Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, China e-mail: [email protected]
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and room temperature until 2015 [2]. Since 2009, organometal halide perovskites have been widely studied in solar energy conversion and the power conversion efficiency approached to 20 % [3, 4]. Beyond solar cells, they were also explored as interesting materials for lowthreshold laser and light-emitting diodes. While, in bulk perovskite materials, the high PLQYs and bright EL emissions can be only achieved at high excitation fluencies or high current density, which have been an obstacle for the device application [5]. Instead, the success in inorganic semiconductor QDs taught us that perovskite QDs may exhibit enhanced PL properties as a result of small particle size dimension (comparable with exciton Bohr radius) and passivation of surface defects [6]. Recently, researchers reported the fabrication of CH3NH3PbBr3 [7] and CsPbX3 (X = Cl, Br, I) [8] QDs by adapting the heating up injection method from II–VI QDs. Though exhibiting high PLQYs, these perovskite QDs can still hardly be launched into mass production for the complicated producing process. In a paper recently published in ACS Nano, Zhong’s group [9] had made a breakthrough on ligand-assisted reprecipitation (LARP) technique to fabricate the CH3NH3PbX3 (X = Cl, Br, I) QDs conveniently at room temperature. The reprecipitation method was a simple way for preparing organic nanocrystals or polymer dots simultaneously through the solvent mixing. Here, as shown in Fig. 1a, the authors used the same principle and simply mix a solution of CH3NH3PbX3 precursors in good solvent (Ndimethylformamide, DMF) into a vigorously stirred poor solvent (toluene, hexane, etc.) to form the organometal halide perovskites. Synthetic process is shown in the animation (video online). At the same time, long-chain organic ligands, such as n-octylamine and oleic acid (OA), were introduced into mixture to control the crystallization of precursors into colloidal quantum dots. It is worth noting
Sci. Bull. (2015) 60(18):1622–1624
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Fig. 1 The synthesis, characterization and LED applications of halide perovskite QDs. a Schematic illustration of the reaction system and process for LARP technique. b Optical images of CH3NH3PbX3 QDs under ambient light and a 365-nm UV lamp and the PL emission spectra of CH3NH3PbX3 QDs. c Schematic diagram and EL spectra of pc-WLED devices using green emissive CH3NH3PbBr3 QDs and red emissive phosphor KSF and the CIE color coordinates corresponding to the CH3NH3PbX3 QDs, pc-WLED devices (blue lines), and NTSC standard (bright area). d Potential applications of perovskite QDs. Reprinted with permission from Ref. [9]. Copyright (2015) American Chemical Society
that this method can achieve CH3NH3PbX3 QDs with high PLQYs (up to *70 %) and narrow-band emission (FWHM * 20 nm) (Fig. 1b). At the same time, this LARP method requires neither heating nor excluding air. The simplification of the method makes it possible to scale up the synthesis. To illustrate the PL enhancements of perovskite QDs, the authors further studied the structure and composition of CH3NH3PbBr3 QDs and factors that influence PL properties of CH3NH3PbBr3 perovskite materials. They found that the as-fabricated CH3NH3PbBr3 QDs are nonstoichiometric due to the Br-rich surface and the proper chemical passivation of n-octylamine and OA on the surface provide good colloidal stability. Moreover, the analysis of temperature-dependent PL spectra of CH3NH3PbBr3 QDs shows an intense increasing of exciton binding energy from *65 meV for bulk counterpart to *375 meV for QDs, which is a result of particle size reduction and surface passivation [9]. This result also suggests that the PL emissions of perovskite QDs mainly take place through exciton recombination rather than the recombination of free electrons and holes. Subsequently, Zhong and his coworkers have fabricated light-emitting prototype devices with green emissive colloidal CH3NH3PbBr3 QDs and red emissive phosphor K2SiF6:Mn4? (KSF). The spectrum and corresponding CIE diagram of the pc-WLED are shown in
Fig. 1c. One of the most exciting features of this new white LED is the wide color gamut, which covers a much larger area than the color space of the National Television Systems Committee standard (*130 % of NTSC 1931) with a matching rate of 96 %. The as-fabricated device has a luminous efficiency of 48 lm/W at a current density of 4.9 mA. These results indicate perovskite QDs a vast potential for applications in wide color gamut display devices. In spite of all the merits mentioned above, this new LARP strategy for perovskite QDs synthesis is still in its early stage and faces some challenges. The thermal and chemical stabilities of organometal halide perovskites still can hardly meet the requirements of white backlight LEDs for display applications. Thus, it requires more efforts on surface modification and materials composite technologies. It is necessary to develop the composite materials and EL devices to impulse the applications of perovskite QDs in lighting and display or even other fields. But yet there is no denying that with all the advantages, such as wide wavelength tunability, inherent narrow-band emission, high PLQYs and low-cost production technology, perovskite QDs will become a very promising candidate for display applications. In addition, researches on perovskite QDs-based EL devices and laser have been launched and we can surely expect the development of perovskite QDs and more mature applications in lighting, display, optical sensors, etc.
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Sci. Bull. (2015) 60(18):1622–1624
References 1. Shirasaki Y, Supran GJ, Bawendi MG et al (2013) Emergence of colloidal quantum-dot light-emitting technologies. Nat Photonics 7:13–23 2. Yang YX, Zheng Y, Cao W et al (2015) High-efficiency lightemitting devices based on quantum dots with tailored nanostructures. Nat Photonics 9:259–266 3. Stranks SD, Snaith HJ (2015) Metal-halide perovskites for photovoltaic and light-emitting devices. Nat Nanotechnol 10:391– 402 4. Wang Q, Chen HJ, Liu G et al (2015) Control of organic-inorganic halide perovskites in solid-state solar cells: a perspective. Sci Bull 60:405–418 5. Deschler F, Price M, Pathak S et al (2014) High photoluminescence efficiency and optically pumped lasing in solution-processed
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6.
7.
8.
9.
mixed halide perovskite semiconductors. J Phys Chem Lett 5:1421–1426 D’Innocenzo V, Srimath Kandada AR, De Bastiani M et al (2014) Tuning the light emission properties by band gap engineering in hybrid lead halide perovskite. J Am Chem Soc 136:17730–17733 Schmidt LC, Pertegas A, Gonzalez-Carrero S et al (2014) Nontemplate synthesis of CH3NH3PbBr 3 perovskite nanoparticles. J Am Chem Soc 136:850–852 Protesescu L, Yakumin S, Bodnarchuk MI et al (2015) Nanocrystals of cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I): novel optoelectronic materials showing bright emission with wide color gamut. Nano Lett 15:3692–3696 Zhang F, Zhong H, Chen C et al (2015) Brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots: potential alternatives for display technology. ACS Nano 9:4533–4542
www.scibull.com www.springer.com/scp
Research Highlight
Halide perovskite quantum dots: potential candidates for display technology Zelong Bai • Haizheng Zhong
Published online: 18 September 2015 Ó Science China Press and Springer-Verlag Berlin Heidelberg 2015
Motivated by the color tunability and narrow-band emission peak of colloidal quantum dots (QDs), the concepts of quantum dot light-emitting diodes (QD-LEDs), based on either the photoluminescence (PL) or electroluminescence (EL) mechanism, have been proposed for a few years [1]. Using QD-LEDs in the backlighting system of liquid crystal display (LCD) can significantly expand the color gamut of display and present vibrant colored images. However, even though CdSe-based QDs have been commercially used in backlighting system, this innovative technique is still suffering from the complicated preparation process, the lack of surface control during process, and unacceptable price of high-quality CdSe-based QDs. Moreover, the developing of high-performance (bright, efficient, and stable) EL devices strongly relies on the precise band engineering of the core and shell as well as surface ligands [2]. To solve these problems, alternative materials with simple process have been much aspired. Halide perovskites exhibit wide wavelength tunability (400–800 nm), narrow-band emission (full width at half maximum, FWHM *20 nm), which make them to be potential candidates for light-emitting applications and have been investigated for at least 20 years. However, their use in light-emitting diodes suffer from the limited photoluminescence quantum yields (PLQYs) at low excitation
Electronic supplementary material The online version of this article (doi:10.1007/s11434-015-0884-y) contains supplementary material, which is available to authorized users. Z. Bai H. Zhong (&) Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, China e-mail: [email protected]
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and room temperature until 2015 [2]. Since 2009, organometal halide perovskites have been widely studied in solar energy conversion and the power conversion efficiency approached to 20 % [3, 4]. Beyond solar cells, they were also explored as interesting materials for lowthreshold laser and light-emitting diodes. While, in bulk perovskite materials, the high PLQYs and bright EL emissions can be only achieved at high excitation fluencies or high current density, which have been an obstacle for the device application [5]. Instead, the success in inorganic semiconductor QDs taught us that perovskite QDs may exhibit enhanced PL properties as a result of small particle size dimension (comparable with exciton Bohr radius) and passivation of surface defects [6]. Recently, researchers reported the fabrication of CH3NH3PbBr3 [7] and CsPbX3 (X = Cl, Br, I) [8] QDs by adapting the heating up injection method from II–VI QDs. Though exhibiting high PLQYs, these perovskite QDs can still hardly be launched into mass production for the complicated producing process. In a paper recently published in ACS Nano, Zhong’s group [9] had made a breakthrough on ligand-assisted reprecipitation (LARP) technique to fabricate the CH3NH3PbX3 (X = Cl, Br, I) QDs conveniently at room temperature. The reprecipitation method was a simple way for preparing organic nanocrystals or polymer dots simultaneously through the solvent mixing. Here, as shown in Fig. 1a, the authors used the same principle and simply mix a solution of CH3NH3PbX3 precursors in good solvent (Ndimethylformamide, DMF) into a vigorously stirred poor solvent (toluene, hexane, etc.) to form the organometal halide perovskites. Synthetic process is shown in the animation (video online). At the same time, long-chain organic ligands, such as n-octylamine and oleic acid (OA), were introduced into mixture to control the crystallization of precursors into colloidal quantum dots. It is worth noting
Sci. Bull. (2015) 60(18):1622–1624
1623
Fig. 1 The synthesis, characterization and LED applications of halide perovskite QDs. a Schematic illustration of the reaction system and process for LARP technique. b Optical images of CH3NH3PbX3 QDs under ambient light and a 365-nm UV lamp and the PL emission spectra of CH3NH3PbX3 QDs. c Schematic diagram and EL spectra of pc-WLED devices using green emissive CH3NH3PbBr3 QDs and red emissive phosphor KSF and the CIE color coordinates corresponding to the CH3NH3PbX3 QDs, pc-WLED devices (blue lines), and NTSC standard (bright area). d Potential applications of perovskite QDs. Reprinted with permission from Ref. [9]. Copyright (2015) American Chemical Society
that this method can achieve CH3NH3PbX3 QDs with high PLQYs (up to *70 %) and narrow-band emission (FWHM * 20 nm) (Fig. 1b). At the same time, this LARP method requires neither heating nor excluding air. The simplification of the method makes it possible to scale up the synthesis. To illustrate the PL enhancements of perovskite QDs, the authors further studied the structure and composition of CH3NH3PbBr3 QDs and factors that influence PL properties of CH3NH3PbBr3 perovskite materials. They found that the as-fabricated CH3NH3PbBr3 QDs are nonstoichiometric due to the Br-rich surface and the proper chemical passivation of n-octylamine and OA on the surface provide good colloidal stability. Moreover, the analysis of temperature-dependent PL spectra of CH3NH3PbBr3 QDs shows an intense increasing of exciton binding energy from *65 meV for bulk counterpart to *375 meV for QDs, which is a result of particle size reduction and surface passivation [9]. This result also suggests that the PL emissions of perovskite QDs mainly take place through exciton recombination rather than the recombination of free electrons and holes. Subsequently, Zhong and his coworkers have fabricated light-emitting prototype devices with green emissive colloidal CH3NH3PbBr3 QDs and red emissive phosphor K2SiF6:Mn4? (KSF). The spectrum and corresponding CIE diagram of the pc-WLED are shown in
Fig. 1c. One of the most exciting features of this new white LED is the wide color gamut, which covers a much larger area than the color space of the National Television Systems Committee standard (*130 % of NTSC 1931) with a matching rate of 96 %. The as-fabricated device has a luminous efficiency of 48 lm/W at a current density of 4.9 mA. These results indicate perovskite QDs a vast potential for applications in wide color gamut display devices. In spite of all the merits mentioned above, this new LARP strategy for perovskite QDs synthesis is still in its early stage and faces some challenges. The thermal and chemical stabilities of organometal halide perovskites still can hardly meet the requirements of white backlight LEDs for display applications. Thus, it requires more efforts on surface modification and materials composite technologies. It is necessary to develop the composite materials and EL devices to impulse the applications of perovskite QDs in lighting and display or even other fields. But yet there is no denying that with all the advantages, such as wide wavelength tunability, inherent narrow-band emission, high PLQYs and low-cost production technology, perovskite QDs will become a very promising candidate for display applications. In addition, researches on perovskite QDs-based EL devices and laser have been launched and we can surely expect the development of perovskite QDs and more mature applications in lighting, display, optical sensors, etc.
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Sci. Bull. (2015) 60(18):1622–1624
References 1. Shirasaki Y, Supran GJ, Bawendi MG et al (2013) Emergence of colloidal quantum-dot light-emitting technologies. Nat Photonics 7:13–23 2. Yang YX, Zheng Y, Cao W et al (2015) High-efficiency lightemitting devices based on quantum dots with tailored nanostructures. Nat Photonics 9:259–266 3. Stranks SD, Snaith HJ (2015) Metal-halide perovskites for photovoltaic and light-emitting devices. Nat Nanotechnol 10:391– 402 4. Wang Q, Chen HJ, Liu G et al (2015) Control of organic-inorganic halide perovskites in solid-state solar cells: a perspective. Sci Bull 60:405–418 5. Deschler F, Price M, Pathak S et al (2014) High photoluminescence efficiency and optically pumped lasing in solution-processed
123
6.
7.
8.
9.
mixed halide perovskite semiconductors. J Phys Chem Lett 5:1421–1426 D’Innocenzo V, Srimath Kandada AR, De Bastiani M et al (2014) Tuning the light emission properties by band gap engineering in hybrid lead halide perovskite. J Am Chem Soc 136:17730–17733 Schmidt LC, Pertegas A, Gonzalez-Carrero S et al (2014) Nontemplate synthesis of CH3NH3PbBr 3 perovskite nanoparticles. J Am Chem Soc 136:850–852 Protesescu L, Yakumin S, Bodnarchuk MI et al (2015) Nanocrystals of cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I): novel optoelectronic materials showing bright emission with wide color gamut. Nano Lett 15:3692–3696 Zhang F, Zhong H, Chen C et al (2015) Brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots: potential alternatives for display technology. ACS Nano 9:4533–4542