Supplementary Information for: Polymer-Nanoparticle Electrochromic Materials that Selectively Modulate Visible. and Near-Infrared Light

Transcription

1 Supplementary Information for: Polymer-Nanoparticle Electrochromic Materials that Selectively Modulate Visible and Near-Infrared Light Christopher J. Barile, Daniel J. Slotcavage, and Michael D. McGehee * Department of Materials Science and Engineering, Stanford University, Stanford, CA * mmcgehee@stanford.edu

2 Figure S1: Thicknesses of films of tested samples as determined by profilometry. Figure S2: Normalized change in percent transmission at 500 nm of PEDOT (black) and at 1350 nm of ITO nanoparticles (red) on ITO electrodes inside a spectroelectrochemical cell containing 1 M LiClO 4 in PC as a function of applied voltage. The near overlap of the switching potentials of the two materials precludes the construction of an electrochromic PEDOT-ITO composite material with independent modulation of visible and NIR light. 2

3 A) B) Figure S3: Transmission spectra of a PMeT film on an ITO-coated glass electrode polarized at V (black) and V (red) vs. Fc + /Fc (A) and the percent transmission at 700 nm as a function of voltage (B) inside a spectroelectrochemical cell containing 1 M LiClO 4 in PC. Figure S3A displays the transmission spectra of an electrochromic cell containing PMeT. When polarized to V, PMeT exists in its undoped reduced form. In this state, PMeT is red in color and possesses a maximum absorbance at 510 nm (red line). Upon electrochemical oxidation, the PMeT film turns deep blue as red and NIR light are absorbed by polarons (black line). Figure S3B plots the transmission of the film at 700 nm as a function of applied voltage. At potentials more positive than V, the transmission begins to decrease as the film begins to oxidize. PMeT and PMe 2 T 2 are structural isomers, making them an interesting case for comparison. In the case of PMe 2 T 2, steric interactions between the two methyl groups in each bithiophenyl monomeric unit disrupt the planarity of the polymer chains and hence decrease the π-conjugation of the polymer. 1 This decrease in conjugation serves to both increase the band gap and oxidation potential of PMe 2 T 2 relative to PMeT. Both effects are advantageous for the polymer-nanoparticle architecture developed here. The higher 3

4 band gap serves to extend the range of visible wavelengths in which the electrode can operate in three distinct modes, and the increased oxidation potential further separates the voltage regimes in which the ITO nanoparticles and the polymer operate, thereby leading to higher contrast ratios. PMe 2 T 2 has a third advantage over PMeT in that it can be more uniformly electropolymerized in common solvents using a commercially available bithiophenyl monomer. 2 The PMeT-ITO Hybrid Electrochromic System In a manner analogous to the PMe 2 T 2 -ITO system, we electropolymerized PMeT onto films of ITO nanoparticles supported on ITO-coated glass electrodes to construct PMeT-ITO hybrid materials. These composite materials also display three distinct modes of visible and NIR modulation that are accessed at three different electrode polarizations (Figure S4A). Like the PMe 2 T 2 -ITO system, the transmission values of the PMeT-ITO system at 700 nm and 1250 nm undergo one and two transitions, respectively, as a function of applied voltage (Figure S4B). However, the voltage regime of the bright & warm state is more negative than the PMe 2 T 2 -ITO film due to the more negative oxidation potential of PMeT. 4

5 A) B) Bright & Warm Bright & Warm Bright & Cool Bright & Cool Dark & Cool Dark & Cool Figure S4: Transmission spectra of a film of the PMeT-ITO composite material on an ITO-coated glass electrode polarized at V (red), V (blue), and V (black) vs. Fc + /Fc (A) and the percent transmission at 700 nm (black) and 1250 nm (red) as a function of voltage (B) inside a spectroelectrochemical cell containing 1 M LiClO 4 in PC. Figure S5 displays cyclic voltammograms (CV) of the composite film and its individual components. The CV of the PMeT polymer alone (red line) displays Faradaic peaks corresponding to the formal oxidation and reduction of the polymer. The onset of the oxidative wave begins at potentials greater than V, which is the voltage at which the transmission characteristics of the PMeT film begin to change (Figure S3B). The CV of the PMeT-ITO hybrid system possesses the main features present in the PMeT features, but also additional features caused by capacitive charging of the ITO nanoparticles (Figure S5, blue line). 5

6 Figure S5: Cyclic voltammograms of films of ITO nanoparticles (black), PMeT (red), and the PMeT-ITO composite material (blue) in 1 M LiClO 4 in PC starting from V at a scan rate of 10 mv/s. Evaluation of PMeT-ITO System Performance Table S1 lists the contrast ratios of the composite material and its individual components at 700 nm and 1250 nm. Whereas the contrast ratio at 1250 nm is 46% for the ITO nanoparticles alone, the contrast ratio induced by the nanoparticles (between bright & cool and bright & warm states) in the hybrid system decreases to 24%. This decrease in contrast ratio primarily originates from absorption of NIR light by the ITO nanoparticles at V. In other words, the switching voltages of the ITO nanoparticles and PMeT polymer are not completely separated. Sample Two States Contrast Ratio ITO Cool (-1.25 V) and Warm (+1.25 V) 46% at 1250 nm PMeT Bright (-1.25 V) and Dark (+1.25 V) 60% at 700 nm PMeT-ITO Bright & Cool (-1.25 V) and Bright & Warm (+0.25 V) Bright & Warm (+0.25 V) and Dark & Cool (+1.25 V) 6 1 % at 700 nm 24% at 1250 nm 14% at 700 nm 40% at 1250 nm Table S1: Contrast ratios for ITO, PMeT, and PMeT-ITO electrochromic cells between different electrode polarizations (vs. Fc + /Fc).

7 Figure S6: Cross-sectional SEM image of PMe 2 T 2 -ITO with reduced PMe 2 T 2. Figure S7: Solar transmittances for visible (400 to 750 nm) and NIR (751 nm to 2200 nm) light for an elelectrochromic cell containing the PMe 2 T 2 -ITO composite material at three different electrode polarizations (vs. Fc + /Fc). 7

8 Figure S8: Thicknesses of PMe 2 T 2 films on ITO-coated glass as determined by profilometry as a function of the number of CV cycles performed during the electropolymerization process. A) B) Figure S9: Transmission spectra of PMe 2 T 2 films electropolymerized using one (black), two (red), three (blue), four (green), and five (orange) CV cycles on ITO-coated glass electrodes polarized at V (A) and V (B) vs. Fc/Fc +. 8

9 A) B) C) Figure S10: Fixed wavelength transmission measurements inside a spectroelectrochemical cell containing 1 M LiClO 4 in PC as a function of time for a film of ITO nanoparticles (A), a film of PMe 2 T 2 (B), and a film of the PMe 2 T 2 -ITO composite material (C) on ITO-coated glass electrodes. The applied potential (vs. Fc + /Fc) of the electrode is switched at the times indicated by the arrows on each of the figures. At time zero, the electrodes had been polarized for five minutes at V, V, and V for the films containing ITO nanoparticles, PMe 2 T 2, and PMe 2 T 2 -ITO, respectively. 9

10 A) B) Figure S11: Transmission spectra of a film of the PMe 2 T 2 -ITO composite material (A) and PMe 2 T 2 (B) on ITO-coated glass electrodes polarized at V (red), V (blue), and V (black) vs. Fc + /Fc inside a spectroelectrochemical cell containing 1 M LiClO 4 in PC after cycling the potential 200 times between V and V at a scan rate of 10 mv/s. Figure S12: Capacitances measured at V vs. Fc + /Fc of electrodes modified with PMe 2 T 2 -ITO (black) and PMe 2 T 2 (red) as a function of CV cycle number. The capacitances of electrodes modified with ITO nanoparticles, PMe 2 T 2, and PMe 2 T 2 -ITO at V vs. Fc + /Fc are 630 µf/cm 2, 420 µf/cm 2, and 110 µf/cm 2, respectively, as measured from their first CV cycle. Polymer filling in pores between the ITO nanoparticles in the PMe 2 T 2 -ITO case potentially explains why the composite material has less capacitance than the film of ITO nanoparticles. Previous work has established that the capacitance of an electrode modified with ITO nanoparticles decreases as it is voltammetrically cycled due to leaching of Sn from the particles. 3 Here, we demonstrate that the capacitances of electrodes modified with 10

11 PMe 2 T 2 and PMe 2 T 2 -ITO also decrease with cycle number (Figure S12). After 200 cycles, the capacitances of the PMe 2 T 2 and PMe 2 T 2 -ITO systems decrease by 30% and 35%, respectively. These values compare to decreases of 20% and 18% in the contrast ratios of the PMe 2 T 2 and PMe 2 T 2 -ITO materials at 700 nm, respectively. References: (1) Arbizzani, C.; Barbarella, G.; Bongini, A.; Mastragostino, M.; Zambianchi, M. Electrochemical and optical properties of poly(3-methylthiophenes) electrosynthesized by 3,3 -, 3,4 - and 4,4 -dimethyl-2,2 -bithiophenes. Synthetic Met. 1992, 52, (2) Arbizzani, C.; Mastragostino, M.; Meneghello, L.; Morselli, M.; Zanelli, A. Poly(3- methylthiophenes) for an all polymer electrochromic device. J. Appl. Electrochem. 1996, 26, (3) Garcia, G.; Buonsanti, R.; Llordes, A.; Runnerstrom, E. L.; Bergerud, A.; Milliron, D. J. Near-Infrared Spectrally Selective Plasmonic Electrochromic Thin Films. Adv. Optical Mater. 2013, 1,