Supporting information for
High-Performance Flexible Electrochromic Device Based on Facile
Semiconductor-to-Metal Transition Realized by WO3·2H2O Ultrathin
Nanosheets
Lin Liang, Jiajia Zhang, Yingying Zhou, Junfeng Xie, Xiaodong Zhang, Meili Guan, Bicai
Pan and Yi Xie*
Hefei National Laboratory for Physical Sciences at the Microscale, University of Science
& Technology of China, Hefei, Anhui, 230026, P.R. China.
S1. The XRD pattern of tungstate-based inorganic–organic nanohybrids.
Figure S1. The low-angle (inset) and wide-angle XRD patterns of tungstate-based
inorganic–organic nanohybrids.
S2. Optical transmittance spectra of WO3·2H2O bulk-based ECD.
Figure S2. Optical transmittance spectra of WO3·2H2O bulk-based ECD under potentials
of +3V and -3V, respectively
S3. Density functional theory (DFT) calculations for bulk WO3·2H2O before and
after Li+ intercalation.
Figure S3. (a) Calculated densities of states for bulk WO3·2H2O. Calculated densities of
states for bulk LixWO3·2H2O with two potential sites for Li+ intercalation: (b) between the
interlamination of WO3[H2O] layer; (c) within the distorted WO5(H2O) octahedrons.
S4. Detailed fabrication and characterization of tungsten oxide dihydrate
(WO3·2H2O) ultrathin nanosheets film.
The successful assembly and transfer of ultrathin materials into large-area thin films
are very significant for device fabrication, particularly in flexible electronics. The detailed
fabrication process can be summarized as below. First, the dispersion of WO 3·2H2O
ultrathin nanosheets was vacuum filtrated onto a cellulose membrane with 0.22 μm pore
size, forming a light-yellow homogeneous thin film, of which the thickness can be well
controlled by tuning the filtrated volume of the solution; Second, the obtained WO3·2H2O
thin film on cellulose membrane was pressed onto the ITO/PET sheet with the assistance
of small amount of ethanol; Last, the film on the ITO/PET sheet was immersed in
acetone, and the cellulose membrane can be gradually dissolved. After an hour, the
acetone was aspirated and the film was reimmersed with fresh acetone again. As a result,
WO3·2H2O ultrathin nanosheets film was successfully transferred onto the ITO/PET sheet.
As shown in Figure S4a, the obtained WO3·2H2O films display transparent character
and tunable thickness. Besides, the WO3·2H2O nanosheets on ITO/PET sheet exhibit
outstanding structural integrity and flexibility as shown in Figure S4b.
Figure S4. (a) Photograph of WO3·2H2O thin film with different thickness transferred
onto ITO/PET sheet, showing transparent character. (b) Photograph of bend WO3·2H2O
film on ITO/PET sheet, demonstrating its integrity and flexibility.
S5. Preparation of WO3·2H2O bulk powder.
In brief, 5 ml of 1.0 M Na2WO4·2H2O solution was dropped into 45 ml of 3 N HCl at 5 °C.
A white precipitate appeared immediately, and then turned to yellow in 30 min. The final
precipitate was centrifuged and washed with HCl and deionized water. The obtained
yellow powder was dried for two days at room temperature. The XRD pattern of
WO3·2H2O bulk powder was shown in Figure S5.
Figure S5. XRD pattern for WO3·2H2O bulk powder, the orange lines give the
corresponding standard pattern of JCPDS Card No.18-1420.
S6. The details for first-principles density functional theory (DFT) calculations.
All calculations were handled by performing density functional theory as implemented
in the Vienna ab initio Simulation Package (VASP) 1. For treating the local W 5d electrons,
the LDA + U
2
was employed, in which the U value of 4.0 eV was selected3. The
single-particle equations were solved using the projector-augmented wave (PAW)4
method with a plane-wave cutoff of 500 eV. A vacuum space of at least 15 Å in y-axis
was applied to avoid the interactions between adjacent sheets. The k-points mesh of
4×4×4 and 4×1×4 were used to sample the Brillouin zone of the bulk WO3 and
nanosheets WO3. For the electronic self-consistency loop a total energy convergence
criterion of 1×10-4 eV was required. Lattice constants and internal coordinates were fully
optimized until residual Hellmann-Feynman forces were smaller than 0.01 eV/Å.
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