Tuning PEDOT:Tos thermoelectric properties through nanoparticle inclusion

Transcription

1 Tuning PEDOT:Tos thermoelectric properties through nanoparticle inclusion Daniela Galliani University of Milano-Bicocca 1 Material Science Department

2 University of Milano- Bicocca Material Science Department Thermoelectrics Research Group Professor Dario Narducci Dr. Bruno Lorenzi Dr. Laura Zulian Dr. Daniela Galliani 2

3 Outline 1. Introduction Conjugated Polymers as Thermoelectric Materials Conjugated Polymer Nanocomposite Energy Filtering Effect 2. Experimental Work Mn 3 O 4 Nanoparticles Nanoparticle Functionalization Hybrid Film Making 3. Results Thermoelectrical Characterization Nanoparticle Influence on Polymer Morphology Humidity Effect 4. Conclusion and Further Developments 3

4 Introduction Conjugated Polymers as Thermoelectric Materials Low thermal conductivity Medium-high electrical conductivity Tunable electronic properties Easy processing Safety Environmental stability Low cost Adaptability to flexible substrate Elschner, A. PEDOT: Principles and Applications CRC Press (2011) Q. Wei et al., Materials (Basel). 8, 732 (2015). 4

5 Introduction Conjugated Polymers as Thermoelectric Materials Poly(3.4-ethylendioxythiophene) PEDOT k= WK 1 m 1 Low TE efficiency Nanostructuration Year efficiencies still low in comparison with inorganic benchmark Bubnova, O. et al. Semi-metallic polymers. Nat. Mater. 13, (2014) 5

6 Introduction Conjugated Polymer Nanocomposite Year Wide variety of materials! Nanomaterial Synthesis Method Composition, polymorph, dimensionality CHOOSING CRITERIA In situ polymerization, solution mixing, physical mixing Q. Wei, M. Mukaida, K. Kirihara, Y. Naitoh, and T. Ishida, Materials (Basel). 8, 732 (2015). 6

7 Introduction E Energy Filtering Effect Vacuum level Amorphous zone Conduction Band E f Valence Band E f E f Polymer Nanoparticle Polymer Crystalline domains N. Neophytou, X. Zianni, H. Kosina, S. Frabboni, B. Lorenzi, and D. Narducci, Nanotechnology 24, (2013). 7

8 Introduction E Energy Filtering Effect Vacuum level Amorphous zone h+ E f Polymer Nanoparticle Polymer Crystalline domains 8

9 Introduction Energy Filtering Effect E Vacuum level E E b E f Polymer Nanoparticle Polymer g(e) 9

10 Introduction Energy Filtering Effect CHOOSING CRITERIA α = 8π2 2 k b 3eh 2 m T π 3n 2 3 E Localization of low velocity holes Decrease of carrier concentration n Intimate contacts between CP and NPs Similar work functions of the CP and the NPs Interfacial barrier height below m 100 mev Increase of average carrier mobility σ = 1 ρ = neμ Chemical interaction between CP and NPs Low velocity holes Choice of CP and NP material Potential barrier g(e) 10

11 Outline 1. Introduction Conjugated Polymers as Thermoelectric Materials Conjugated Polymer Nanocomposite Energy Filtering Effect 2. Experimental Work Mn 3 O 4 Nanoparticles Nanoparticle Functionalization Hybrid Film Making 3. Results Thermoelectrical Characterization Nanoparticle Influence on Polymer Morphology Humidity Effect 4. Conclusion and Further Developments 11

12 Experimental Work Mn 3 O 4 Nanoparticles «Coprecipitation» method Mn 3 O 4 p-type material work function: 4,4 ev Starting salt solution NPs suspension Thanks to Dr. Simone Battiston IENI-CNR, Padova Starting salt Size control agent Reagent T ( C) Size SEM determined (nm) MnCl 2 4H 2 O Ethanolamine H 2 O 25 25±6 S. Lei, K. Tang, Z. Fang, and H. Zheng, Cryst. Growth Des. 6, 1757 (2006) 12

13 Experimental Work Nanoparticle Functionalization Phase separation Homogeneous dispersion 13

14 Experimental Work Nanoparticle Functionalization Mn 3 O 4 NP Mn 3 O 4 NP Mn 3 O 4 NPs Glutaryl-EDOT (0,5 M) Imidazole In situ polymerization Ethanol Mn 3 O 4 NP Cyclomixed for 26 hours Glutaryl-EDOT 14

15 Experimental Work Hybrid Film Making Blade Coating Mn 3 O 4 NPs decorated with glutaryl-edot EDOT Polymerization in situ FeTos 3 Base Solvent T=-20 C Substrate (Kapton ) Blade 1) Solution deposition 2) Solution spreading 3) Film drying 15

16 Outline 1. Introduction Conjugated Polymers as Thermoelectric Materials Conjugated Polymer Nanocomposite Energy Filtering Effect 2. Experimental Work Mn 3 O 4 Nanoparticles Nanoparticle Functionalization Hybrid Film Making 3. Results Thermoelectrical Characterization Nanoparticle Influence on Polymer Morphology Humidity Effect 4. Conclusion and Further Developments 16

17 dry ( -1 cm -1 ) Results Thermoelectric Characterization [NP] (cm -3 ) σ dry (Ω -1 cm -1 ) α dry (µvk -1 ) PEDOT:Tos 0 242±9 15.8±0.9 HF ±9 14.8±0.5 HF ±6 15.5±0.7 HF ±4 15.0±0.2 HF ±3 15.5± [NP]: NP density σ: electrical conductivity α: Seebeck coefficient e: electronic charge ( C) σ = epμ σ = ep(μ 0 + μ 1 e NP N 0) p: charge carrier density (holes) [cm -3 ] μ: charge carrier mobility [cm 2 /(V s)] μ 0, μ 1, N 0 : constants 0 1x x x x x10 15 NP concentration (cm -3 ) 17

18 - Nanoparticle Influence on Polymer Results Morphology Electronic transport through chain backbone Electronic transport through π-π stacking interaction 18

19 Results Detrimental effect on σ: Water interposition between polymer chains Humidity Effect Beneficial effect on σ: Counterion solvatation nm Negligible in NP presence Loss in hole mobility Gain in hole density H. Wang et al., Adv. Energy Mater. 5, 1 (2015). 19

20 Normalized electrical conductivity (arb. un.) Results 1,5 1,4 Humidity Effect HF1 HF2 HF3 HF4 PEDOT:Tos 1,3 1,2 1,1 1, Humidity (RH%) ep( x,[ NP] ) m m e w 0 1 [ NP]/ N dry ([ NP p]) xw 0 1e [ NP]/ N 0 z p( x,[ NP] ) p(0,[ NP]) x p 1 ( [ NP]) x w w 0 w xw x 0 w 0 [NP]: NP density σ: electrical conductivity e: electronic charge ( C) x w : water molar fraction β: dimensionless function (β>0) 20

21 Results Humidity Effect dry (RH; x, x 0) e 0 1 [ NP]/ N 0 dry ( -1 cm -1 ) PEDOT:Tos HF1 HF2 HF3 HF4 [NP]: NP density σ: electrical conductivity β, δ x, x 0 : model parameters RH: relative humidity RH 21

22 Results Humidity Effect Understanding parameters dry (RH; x, x 0) e 0 1 [ NP]/ N 0 2,50 2,25 2,00 1,75 1,50 1,25 1,00 0 1x x x x x10 15 NP concentration (cm -3 ) Parameter β (variation of p due to x w ) exponential decay vs [NP] Water molecules sequestration by NPs 1,0 Broader x w vs RH curves for higher [NP] samples x w 0,5 Higher [NP] samples 0,0 0,0 0,2 0,4 0,6 0,8 1,0 RH 22

23 Conclusion Conclusions and Further Developments Results obtained: A novel protocol to obtain hybrid material CP/INPs has been developed Understanding of morphology related aspects of the developed system NPs Electrical properties Morphology 23

24 Conclusion Conclusions and Further Developments Further Developments: Development of a strategy to avoid nanomaterial detrimental effect on morphology 1. Implement polymerization and post-polymerization treatments to favor the rearrangements of NPs (head-to-tail) 2. Using 1D nanomaterial 24

25 Thank you for your kind attention! Aknowledgments University of Milano-Bicocca Thermoelectrics Group: Professor Dario Narducci, Dr. Bruno Lorenzi, Dr. Laura Zulian LaSMO Group (Organic Synthesis): Professor Luca Beverina, Dr. Mauro Sassi Electrochemistry Group: Professor Riccardo Ruffo AFM Characterization: Dr. Silvia Trabattoni Co-Supervisor: Dr. Luca Bertini IENI-CNR Padova SEM Characterization: Dr. Simone Battiston University of Pavia Co-Supervisor: Professor Umberto Anselmi-Tamburini 25

26 Further explanations Conductivity in CP 26

27 Transmittance (%) Further explanations NP IR Characterization 100,0 99,9 99,8 99,7 99,6 99, Wavenumber (cm -1 ) 407 cm cm cm cm -1 Mn-O stretching modes in tetrahedral sites 517 cm -1 Mn-O stretching modes in octaedral sites 407 cm -1 Mn 3+ -O vibrational modes in octahedral sites 27

28 Further explanations Synthesis of glutaryl-edot 28

29 Absorbance (arb. un.) Further explanations UV-vis Characterization of decorated NP 1,0 Glutaryl-EDOT in EtOH Glutaryl-EDOT functionalized Mn 3 O 4 NPs in EtOH Mn 3 O 4 NP 0,8 LMCT 0,6 0,4 LMCT 0,2 0, Wavelength (nm) 29

30 Further explanations Power Factor Values [NP] (cm -3 ) σ dry (Ω -1 cm -1 ) α dry (µvk -1 ) PF dry (µwk -1 m -1 ) PEDOT:Tos 0 242±9 15.8± ±0.8 HF ±9 14.8± ±0.7 HF ±6 15.5± ±0.5 HF ±4 15.0± ±0.6 HF ±3 15.5± ±0.3 30

31 Further explanations m m Humidity Effect Understanding the model p [ NP]/ N0 ep( xw,[ NP] ) 0 1e p( xw,[ NP] ) p(0,[ NP]) xw p0 1 ( [ NP]) xw xw x w 0 ([ NP]) x e dry w 0 1 [ NP]/ N 0 Rault s equation for non-ideal solution: P ( 0) w / P P a 0 w w 0 / P ( x ) w Water activity approximated as a standard sigmoidal: a w 1 x w x0 1 xw x 0 ( xw ) csch sinh cosh sech 2 x 2 x 2 x 2 x Water molar fraction according to the water activity formula: x x 0 1 (RH 1) tanh coth coth (RH;, x ) RH 1 x x w x x 0 dry (RH; x, x 0) e 0 1 [ NP]/ N 0 [NP]: NP density σ: electrical conductivity e: electronic charge ( C) x w : water molar fraction β: dimensionless function (β>0) p: charge carrier density (holes) [cm -3 ] μ: charge carrier mobility [cm 2 /(V s)] μ 0, μ 1, N 0 : constants P 0 : 1 bar P w (0) : equilibrium water pressure a w : water activity RH: relative humidity 31

32 Further explanations Record ZT value at room temperature 32