Direct ection n fo for d dev evel elopment ent o of nea f - PowerPoint PPT Presentation

Direct ection n fo for d dev evel elopment ent o of nea f near infr nfrared ed-dy dyes s for or dye ye-se sensit sitiz ized d so sola lar c cells lls from rom the he view ew p point nt of el f elect ectron i n inj nject ection n and nd cha charge e reco ecombina nation Shuzi Hayase Kyushu Institute of Technology (National Institute) Kitakyushu, Fukuoka, Japan, 808-0196, Japan Tokyo 1

Collaborator Kyushu Institute of Technology Shyam S. Pandey Yuhei Ogomi Nippon Steel & Sumikin Chemical Co., LTD Yoshihiro Yamaguchi Universidad de Castilla-La Mancha Abderrazzak Douhal Boiko Cohen Marcin Aiolek Gustovo de Miguel Michal Zitnan, Maria Jose Marchena Barriento, Sofia Kapetanaki

Dye sensitized solar cells (DSCs) B. O’Regan and M. Graetzel Nature , 1991 , 35 3 , 737 Electrolyte I - /I 3 - (Acetonitrile, ethylene carbonate, molten salts, etc.) Dye Ti Ti O O CO CO TiO 2 TiO 2 N N N COOH HOOC N Ru SCN NCS 10-20nm OHP257 TiO 2 layer: 10-20 μ m Electrolyte layer: 30 μ m SnO 2 /F 3

Photovoltaic Performance Comparison Certified efficiency AM1.5G ,1000W/m 2 Commercially 25.0% available 20.4% 19.6% 20 15% (target) Efficiency （％） 16.7% 11.9% 10.7% 10.1 % 10 Sharp Mitsubishi Chem. 0 C-Si Poly-Si CIGS CdTe a-Si DSC OPV Organic PV CIGS: CuInGaS(Se) DSC:Dye-sensitized solar cell OPV: Organic thin film PV M. A. Green, K. Emery, Y. Hishikawa, W. Warta, and E. D. Dunlop, Prog. Photovolt: Res. Appl. 2013; 21:1-11.

Spectrum matching for DSC to sun light spectrum (AM1.5) Increase in Voc Ti Ti O O CO Increase in Jsc (New dye, or tandem, hybrid) CO N N N COOH HOOC 36 mA ・ cm -2 N Ru 20% SCN NCS OHP257 32 mA ・ cm -2 18% FF:0.75 IR dye Voc: 0.75 Ru dye 25-26 mA ・ cm -2 14-15% 5

Efficiency expectation IPCE 80%, FF 0.75

0.8 Cocktail dyes N-719 Black dye 0.7 New NIR dyes to be 0.6 developed B 0.5 Conventional Ru dye IPCE 0.4 A 0.3 0.2 0.1 0 300 400 500 600 700 800 900 1000 Wavelength (nm)

Requirement for development of Near Infrared Dye dye e - TiO iO 2 co cond nd. b band nd LUMO ⊿ G1 G1 0. 0.9eV 9eV e - hν I - / I 3 - ⊿ G2 HOMO How to decrease ⊿ G1 and ⊿ G2 with maintaining fast electron shift Collaboration of solar cell researchers with photo-physics researchers

Collaboration of J Co Japan si side with Spain si side Hayase group Douhal group (Solar cell-based research) (Time resolved study) Molecular orbital calculation Time resolved study Dye syntheses Samples Substrates Solar cell performance Analyses of electron injection evaluation and dye regeneration Dynamics Fundamental analyses on solar cells Extraction of items determining sola cell efficiency Propose high efficiency dyes

Femto-second Transient Absorption: SQ-41 0.00 0.1 1.00 Electrolyte Life-tim A B 1.00 ∆ A -0.01 β = − τ f x ( ) A exp[( t ) ] I 6.7 ps ΙΙ 0.75 Normalized ∆ A II 11.1 p -0.02 Ι 700 725 750 775 0.75 Wavelength / nm 0.50 III 4.9 ps ΙΙΙ Normalized ∆ A 0.0 No electrolyte No 2.5 ps 0.25 ΙΙ 0.50 ∆ A 0.00 0 ps 0 1 2 3 4 5 Ι Time / ps 1 ps -0.1 ΙΙΙ 3 ps 0.25 Ground State 7 ps Bleaching 42 ps No electrolyte 0.00 -0.2 0 10 20 30 40 50 450 500 550 600650 700 750 Time / ps Wavelength / nm Change in spectral SQ radical cation shape at longer delay. formation; Signal beyond 2 ns. Electron injection • + + − + → SQ * ( S ) TiO SQ TiO ( e ) 1 2 2

Research Collaboration ✓ Research discussions: 5 times March 2010 (Spain), May 2011 (Spain), Aug. 2011 (Japan), Sep. 2011 (Spain), June 2012 (Sweden) ✓ Dr. Gustovo de Miguel visited us in Japan and joined the research in Aug. 2011. ✓ Provided 15 dyes and 15 substrates (encapsulated) to Douhal Lab.

Development of near IR dyes for combination with TiO 2 (~900 nm) ✔ HOMO-LUMO energy level dye adjustment LUMO e - TiO iO 2 co cond nd. b band nd ✔ LUMO orbital shape 0.2eV 0. 2eV ✔ Electron injection energy barrier ✔ Excitation life time 0.9eV 0. 9eV e - ✔ Molecular orbital calculation hν ✔ Dye syntheses tech. I - / I 3 - ✔ Cell structure and cell analyses HOMO ✔ Time resolved spectroscopy 12

Simulation results of molecular orbital on organic dye 13

Model dyes: Sharp absorption spectra Side chain effect SQ dyes HOOC COOH O N N + O - R R

Designing of molecular structures after MO calculation HOOC O COOH N N + O - HOOC O COOH N N + O - HOOC O COOH HOOC N N + O - O COOH HOOC COOH N O N + O - N N + O - SQD-2 SQD-4 SQD-8 SQD-12 SQD-18 (alkyl chain=2) (alkyl chain=4) (alkyl chain=8) (alkyl chain=12) (alkyl chain=18) HOOC COOH COOH O O HOOC N N N + O - O N SQD-4F3 SQD-0 (alkyl chain=0) F F F F F F

HOMO-LUMO level of synthesized dyes -3 LUMO Energy vs E Vac (eV) LUMO Δ G1 SQ-Fluoro TiO 2 CB -4 TiO 2 CB Introduction of F alkll decreases HOMO and LUMO I - /I 3 - - /I - I 3 -5 Δ G2 HOMO HOMO SQ-Fluoro -6 0 5 10 15 20 Alkyl chain length HOMO-LUMO level can be controlled within 0.6 eV by varying substituents

Effic fficie iency vs y vs. Alk lkyl yl chain ain le length th 2.80 2.40 Efficiency [%] 2.00 1.60 1.20 0.80 0.40 0.00 0 2 4 6 8 10 12 14 16 18 20 Alkyl Chain Length

Adsorption scheme for SQ dyes O - O - O - O - O - O - N + N + N + O - N N N N + N + N + N N N N + N O O O O O O O TiO 2 TiO 2 HOOC O COOH N N + O - HOOC O COOH N N + O - HOOC O COOH HOOC N N + O - O COOH HOOC COOH N N + O O - N N + O - SQ-2 SQ-4 SQ-8 SQ-12 SQ-18 (alkyl chain=2) (alkyl chain=4) (alkyl chain=8) (alkyl chain=12) (alkyl chain=18)

Main structure responsible for near IR dyes

Dyes with extended conjugation (SQD2) - O COOH N N O SQ-12 Chemical Formula: C 36 H 40 N 2 O 4 Exact Mass: 564.2988

1.2 1. 8 Absorbace (Norm.) 27 31 0. 0.8 16 70 0. 0.4 0 500 500 600 600 700 700 800 800 900 900 Wavelength (nm) 21

Model SQ dyes TiO2 27 31 16 70 8 LUMO LUMO -3.3 LUMO LUMO LUMO Conduction band Vacuum level [eV] -4.3 I - /I 3 - HOMO HOMO HOMO Redox potential -5.3 HOMO HOMO -6.3 -7.3 TiO 2

One of results of collaboration research

Model Squaraine Sensitizers 1. Chain length ----- SQ-2 and SQ-4 2. Nature of substituents----SQ-4 and SQ-26 3. Molecular Asymmetry------------- SQ-26 and SQ-41

Electronic Absorption Spectra ε = 2-3 X 10 5 dm 3 .mole -1 .cm -1 1.0 SQ 41 Normalized absorbance SQ 26 0.8 SQ 4 SQ 2 0.6 0.4 0.2 0.0 550 600 650 700 750 Wavelength / nm

Energy Band Diagram ⊿ G1 CB TiO 2 SQD4F6 I - /I 3 - ⊿ G2 LUMO change: Electron injection SQD8 SQ4/4F3 HOMO change: Dye generation Anchor group: Substitution effects:

Photovoltaic Characteristics Pho hotocur current ent Act ction n Spect pectra 0.7 SQ-2 0.6 SQ-4 SQ-26 SQ-41 0.5 IPCE 0.4 0.3 0.2 0.1 0 400 500 600 700 Wavelength (nm)

Time Resolved Investigations Time-resolved techniques Femtosecond Transient Absorption Spectroscopy Nanosecond Flash Photolysis -3 SQ Dye Experimental Conditions:  SQ-dyes adsorbed on TiO 2 ②  SQ-dyes adsorbed on ZrO 2 ⊿ G1 To determine the electron injection efficiency ! ① ③ -4  Time resolved investigations in ⑤ the presence of electrolyte TiO 2  Time-resolved investigations ④ in the absence of electrolyte To determine the Dye Regeneration efficiency ! -5 I-/I3- ⑥

Electron injection

Electron Injection ( ②） Relationship between ⊿ G and injection rate constant -3 SQ Dye ② ⊿ G1 0.9 ① ③ SQ4(SQD8) 0.8 -4 0.7 SQ41(SQ4F3) 0.6 SQ2(SQD2) ⑤ 0.5 ⊿ G TiO 2 0.4 Better 0.3 ④ SQ26(SQD4F6) 0.2 0.1 -5 I-/I3- 0 ⑥ 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Injection rate constant /10(-9)/s No apparent relation between ⊿ G1 and injection rate constant Electron injection efficiency is governed by factors other than ⊿ G1

Electron Injection ( ②） Relationship between ⊿ G and injection rate constant -3 SQ Dye ② ⊿ G1 Common trend 0.9 Better ① ③ SQ4(SQD8) 0.8 -4 0.7 SQ41(SQ4F3) 0.6 SQ2(SQD2) ⑤ 0.5 ⊿ G TiO 2 0.4 0.3 ④ F facilitates the electron SQ26(SQD4F6) 0.2 injection with the same ⊿ G1 0.1 -5 I-/I3- 0 ⑥ 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Injection rate constant /10(-9)/s High electron injection can be realized with lower ⊿ G1 by using dyes with F atoms

Dye regeneration

Dye generation( ⑥） Relationship between ⊿ G2 and dye regeneration -3 SQ Dye ② Better for high efficiency ① ③ Common trend 0.9 -4 0.8 SQ4(SQD8) 0.7 Gap (redox-HOMO)/eV ⑤ 0.6 SQ41(SQ4F3) 0.5 ④ 0.4 SQ2(SQD2) 0.3 SQ26(SQD4F6) 0.2 -5 I-/I3- 0.1 ⑥ 0 ⊿ G2 0 0.2 0.4 0.6 0.8 1 1.2 Regeneration efficiency High dye generation with Low ⊿ G2

Possible explanation for high efficiency dye generation with low ⊿ G2 F F F I - O N COOH HOOC N TiO 2 O HOMO Chemical Formula: C 36 H 34 F 6 N 2 O 6 Exact Mass: 704.23 F Symmetrical-SQ-26 F F