量子ドット ナノシートを用いた色変換素子の開発

Transcription

1 量子ドット ナノシートを用いた色変換素子の開発 東京工業大学 物質理工学院宮内雅浩 1 多色 高速変換が可能なリモートフォトクロミック Miyauchi et al. Adv. Funct. Mater. 20, 4162, Miyauchi et al. Nanoscale 7, 12510, 水溶液がインク 酸素が消しゴムとして働く色変換素子 Miyauchi et al. Chem. Commun. 47, 8596, Miyauchi et al. J. Mater. Chem. C 2, 3732, Quantum Dot 2 H + Nanosheet Nanosheet e - Aluminum

2 Limitation of Photochromism and Electrochromism in WO 3 C. B. O 2 Limitation of WO 3 for chromic device 2.8 ev V. B. W 5+, W Color Limitation (Yellow Blue) 2. Excitation Wavelength (λ < 450 nm) 3. Slow decoloration rate Quantum dots (QDs): Nano-size (Nanosheet): tunable color! quick response!

3 Materials in the present study Nanosheet (Cs 4 W 11 O ) and QD (CdS) pyrochlore structure Exfoliation ( αh v ) CdS 5 nm 8cycles 4cycles 2cycles 1cycle 0cycle TiO 2 QDs (αh v ) 1 / TiO 2 Cs 6 W 11 O 36 bulk Cs 4 W 11 O nanosheet Photon Energy / ev 0.0 transparent electron trapping large surface area, quick response color tunable facile wet synthesis (SILAR method) Fukuda et al. ACS Nano 2, 1689, Miyauchi et al. Appl. Catal. B Environ. 179, 113, 2015.

4 Fabrication of QDs/ Nanosheet Film Nanosheets: Exfoliation Solid phase reaction Cs 2 CO 3 WO h Thin Film: Spin or Dip coating Quantum Dots: SILAR Successive Ionic Layer Adsorption and Reaction Proton exchange Cs 6 W 11 O 36 12M HCl 2days substrate Exfoliation H 2 Cs 4 W 11 O 36 TBAOH 10days Colloidal nanosheets suspension substrate substrate visible light 1 Remote photochromism water, oxygen 2 Color change in water glass substrate Color change Kelvin probe forced microscope (KFM) Aluminum Color change Comparison with particles film ph dependence

5 Structure of Cs 4 W 11 O Nanosheets 200 nm TEM AFM FE-SEM:Surface 500 nm FE-SEM: Cross Section

6 Tunable Color by QDs Size SILAR method QDs Layered Nanosheet 4cycle Layered Nanosheet+QDs SILAR 回数 0cycle 1cycle 2cycles 4cycles 8cycles QDs size 3.7 nm 5.0 nm 5.9 nm 6.4 nm Bandgap Energy 3.6 ev 2.8 ev 2.6 ev 2.4 ev 2.3 ev Tunable Quantum Size effects Empirical dependence of QDs size: D=( )λ 3 +( ) λ 2 -( ) λ+13.29

7 Remote Photochromism under Visible Light Color UV-vis Excite only QDs Decolor XPS

8 Action Spectra for Remote Photochromism

9 KPFM Analysis of QDs/ Nanosheet (i) (a) trapped CdS QD (ii) Cs 4 W 11 O 36- nanosheet (iii) Mapping of work function (i) (b) (i) (c) QDs Cs 4 W 11 O mica (ii) (iii) (ii) (iii) positive before light irradiation after light irradiation

10 Decoloration Process Nanosheet Vs. Conventional WO 3 Particles Oxygen is accepter Fast decoloration Fast Slow

11 Repeated Property Quantum Dot visible light dark Excitation light: Xe lamp Nanosheet 量子ドットのサイズによって色制御可能 高速 可逆色変換 TON 8000( 生成した正孔 / 担持 CdS 量 )

12 量子ドット ナノシートを用いた色変換素子の開発 1 東京工業大学 物質理工学院宮内雅浩 1 多色 高速変換が可能なリモートフォトクロミック Miyauchi et al. Adv. Funct. Mater. 20, 4162, Miyauchi et al. Nanoscale 7, 12510, 水溶液がインク 酸素が消しゴムとして働く色変換素子 Miyauchi et al. Chem. Commun. 47, 8596, Miyauchi et al. J. Mater. Chem. C 2, 3732, Quantum Dot 2 O 2 H + O 2 - Nanosheet Nanosheet e - Aluminum

13 Novel Chromic WO 3 /Al Device WO 3 Al in aq. WO 3 +e - +H + H + W 5+ O 3 Al Al 3+ +3e - in air Aqueous acid solution: Ink Oxygen molecules in air: Eraser Electroless Galvanic Inks on Inorganic WO 3 /Al Boards Miyauchi et al. Chem. Commun. 47, 8596, 2011.

14 Working Principle 空間電荷層の厚み d dd = 着色 ( 酸性溶液 ) 2εεεε 0ΔEE eeee WO 3 の場合 ~2000 nm 消色 ( 空気中 ) e e e e e e e e e e e e e e e - Al H + Al O 2 O 2 - e e e e e e e e e e e e e e Al 3+ Al 3+ Dissolution Al Potential (V) vs NHE Al Al 3+ +3e - Al 3+ /Al: V E 0 V (H + / H 2 ) WO 3 +e - +H + H + W 5+ O 3 W 6+ /W 5+ : +0.3V Al WO 3 WO 3 粒子を使って原理検証 ナノシートによる高性能化 O 2 Recovery O 2 -

15 XRD and XPS for WO 3 /Al Intensity (a. u.) Monoclinic WO 3 H 0.5 WO 3 Al (i) (ii) Intensity (a. u.) 50 W-4f Binding energy (ev) (i) (ii) (iii) Intensity (a. u.) 545 O-2p Binding energy (ev) (i) (ii) (iii) (iii) Intensity (a. u.) Al-2p Al-2p (i) (ii) (iii) (i) (ii) (iii) Initial Dipping in water (ph=3) Exposure to air 2 theta (degree) (i) (ii) (iii) Initial Dipping in water (ph=3) Exposure to air Binding energy (ev) 70 65

16 Repeatability of the Reversible Color Change in WO 3 /Al Absorbance at 550 nm Initial After repeated evaluation Time (min)

17 WO 3 /Al Structures by Various Processes in acid in air (a) Polycrystalline WO 3 coated on Al foil in acid in air (b) Polycrystalline WO 3 coated on Al coated glass substrate (Al was deposited on glass substrate by sputtering) in acid in air (c) Amorphous WO 3 coated on Al plate by pulsed layer deposition method.

18 From Particles To Nanosheets 20 nm 2nm 200nm Aluminum WO 3 Particles To achieve good properties Aluminum Cs 4 W 11 O Nanosheets Advantages of Nansheets Coloration: Better junction between nanosheets Decoloration: Short length for electron transfer Transparency: Large bandgap by quantum size effect

19 TEM Images of Particles and Nanosheets WO3 nanoparticle (比較例) Cs4W11O362- nanosheet

20 Color Change of Nanosheet/ Al Board Fast decoloration rate t 1/2 = 630 s t 1/2 =25s Coloration:in Decoloration:in acid solution air Absorbance at 600nm Blue Cs 4 W 11 O WO 3 particle Cs 4 W 11 O 2-36 nanosheet Transparent Cs 4 W 11 O time /s

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22 量子ドットの元素戦略 量子ドットとして硫化物 ( クラーク数 15) を利用する Al Si P S Fe Co Ni Cu Zn Ga Ge As Se Tc Rh Pd Ag Cd In Sn Sb Te 太陽電池や量子ドットに使われる多くの既往の化合物 : 毒性 希少金属を含む (CIGS CdTe) 安価 安全な元素からなり 可視光を吸収する化合物 : SnS (BG= 1.3 ev) Cu 2 ZnSnS 4 (CZTS) (BG= 1.2 ev)

23 Future Work 1: Ubiquitous QDs elemental strategy ubiquitous S Sn theory device H 2 Miyauchi et al. Chem. Commun. 52, 7470, Miyauchi et al. J. Phys. Chem. C 122, 21695, 2018.

24 Future Work 2: Surface Modification For more stable: PEDOT coating PEDOT QD metal TiO 2 oxide For more efficient: SiO 2 coating SiO 2 Miyauchi et al. Appl. Catal. B Environ. 179, 113, TiO 2 QD Miyauchi et al. Appl. Phys. Lett. 96, , 2011.

25 Acknowledgement 本研究は公益財団法人日本板硝子材料工学助成会の支援のもと おこないました ここに感謝の意を表します 積水樹脂技術研究所様にも深く御礼申し上げます 近藤彰彦 ( 卒業生 ) 現日本特殊陶業 ( 株 )