Hybrid Photoanodes Based on Nanoporous Lithium Titanate Nanostructures in Dye-sensitized Solar Cells

doi:10.15541/jim20150094

Abstract

Abstract:

Li₄Ti₅O₁₂ with nanoporous feature and good conductivity was used to enhance the photoelectrochemical performance of traditional nanocrystalline TiO₂ photoanodes in Dye-sensitized Solar Cells (DSSC). Using tetrabutyl titanate and lithium hydroxide as raw materials, the spinel Li₄Ti₅O₁₂was obtained from common Sol-Gel, solvethermal and annealing processes. The dependence of the crystallinity, morphology and pore structure of the Li₄Ti₅O₁₂ powders on the annealing temperature were investigated. Li₄Ti₅O₁₂-TiO₂ hybrid photoanodes were prepared by the doctor-blade method using the slurry of TiO₂nanocrystallite which was blended with Li₄Ti₅O₁₂powders. The effects of the mass ratio of Li₄Ti₅O₁₂ to TiO₂, the crystallinity and the porous structure of Li₄Ti₅O₁₂ powders on the performance of DSSC were examined. Results show that with the annealing temperature increasing, the crystallinity of the Li₄Ti₅O₁₂ powders is enhanced, the crystallite size increased obviously, and the specific surface area decreased dramatically. The Li₄Ti₅O₁₂-TiO₂hybrid photoanodes exhibit higher dye-loading capacity and lower resistance at TiO₂/dye/electrolyte interface than does the pure TiO₂ counterpart, accompanied by higher J_sc (J_sc=13.91 mA/cm²) and V_oc(V_oc=0.8 V) values than by the TiO₂ photoanode. The highest conversion efficiency (7.011%) is achieved by 1wt% Li₄Ti₅O₁₂ hybrid cell, which is 30% higher than by the TiO₂nanocrystallite counterpart (5.384%).

Key words: dye-sensitized solar cells, hybrid photoanodes, lithium titanate, photoelectric conversion

CLC Number:

TM914

HU Xue-Mei, GU Zheng-Ying, LI Xiao-Min, GAO Xiang-Dong, SHI Ying. Hybrid Photoanodes Based on Nanoporous Lithium Titanate Nanostructures in Dye-sensitized Solar Cells[J]. Journal of Inorganic Materials, 2015, 30(10): 1037-1042.

Figures/Tables 9

Fig. 1 XRD patterns of LTO samples after heat-treatment at different temperatures (a) 500℃; (b) 600℃; (c) 700℃

Fig. 2 SEM images of LTO powders after heat-treatment at different temperatures (a, b) 500℃; (c, d) 600℃; (e, f) 700℃

Fig. 3 Pore size distribution curves for LTO powders after heat-treatment at different temperatures

Fig. 4 Surface morphology of TiO2 photoanodes (a) and surface (b) and cross-section (c) morphologies of LTO-TiO2 hybrid photoanodes

Fig. 5 (a) Transmission spectra of 5wt%LTO-TiO2 hybrid photoanodes after heat-treatment at different temperatures and (b) hybrid photoanodes with different LTO-TiO2 ratios after heat-treatment at 700℃

Fig. 6 Absorption spectra of photoanodes with different LTO- TiO2 hybrid photoanodes

Fig. 7 J-V curves of DSSC devices based on LTO-TiO2 hybrid photoanodes

Table1 Photovoltaic properties of LTO-TiO2 DSSC

Ratio	V_oc/V	J_sc/(mA•cm^-2)	FF	η/%	R_ct/?	τ/ms
TiO₂	0.659	11.854	0.688	5.384	92.72	4.24
0.5wt%LTO-TiO₂	0.759	11.323	0.645	5.547	42.36	4.24
1wt%LTO-TiO₂	0.797	13.909	0.635	7.011	43.48	5.06
2wt%LTO-TiO₂	0.764	12.873	0.633	6.246	41.44	5.06
5wt%LTO-TiO₂	0.718	10.223	0.657	4.818	89.71	7.51

Fig. 8 Electrochemical impedance spectra of different LTO-TiO2 DSSC (a) Nyquist plots; (b) Bode plots

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