| Dye sensitized solar cell(DSSC) as the third generation of solar photovoltaic device has gained widespread attention during the past two decades attributed to its simple manufacturing process and low fabrication cost. It has potentially broad application in the fields of new energy. As we all know, the dye loading amount, light capture efficiency and electrical transport behavior has been significant influenced by the photoanode in DSSC, which is also crucial to the photoelectric conversion efficiency of the device. Zn O as the II-VI wide bandgap semiconductor has been considered to be the most promising candidate for replacement TiO2 material due to its abundant resources, high electron mobility, appropriate conduction band edges and facile preparation in low temperature, and the morphology controllable. Currently, the energy conversion efficiency of ZnO based DSSC is generally low. Thus, it is necessary to carry out a systematic research on DSSC, which will establish some experimental basis for its application in photovoltaic devices.A traditional photoanode film contains a porous nanoparticles structure with a larger specific surface area, but the electron transfer rate is very poor. 1 D nano material has a lower larger specific surface area, but the electron transfer rate is very high, which can provide a transportation path for electrons. Therefore, compositing 1 D nano material into nanoparticles can benefit to the electrical transport properties rising. In recent years, researchers have found that a higher temperature could damage the efficiency and life of the DSSCs when the operation. Actually, the solar spectrum in the near-infrared light can’t be used in photovoltaic conversion, but causing the temperature increases. Bi2Te3 is considered to be the best thermoelectric materials, which could possess a higher figure of merit at around room temperature, near to 1. Therefore, it is necessary to study the composite photoanode with ZnO nanoparticles and 1 D Bi2Te3 nanotubes, which can further improve the efficiency of the DSSC by using “light to heat” effectively.In this paper, we have prepared ZnO nanoroads array photoanode, ZnO nanorods/ZnO nanoparticls composite photoanode and ZnO nanorods/Bi2Te3 nanotubes composite photoanode, and assembled DSSC. The morphologies, microstructure and composition of this photoanodes were investigated by XRD, SEM, TEM and UV respectively. The photocurrent density-voltage(J-V), external quantum efficiency(EQE), and electrochemical impedance spectroscopy(EIS) were applied to analyze the influence of the Ga concentration in Zn O seed layer, ZnO nanorods content and Bi2Te3 nanotubes content in composite anode for the photovoltaic performance and electron transport process of the DSSC, respectively.The main contents are list as follows:(1) Zinc oxide(ZnO) nanorod arrays were grown on FTO substrates with a Ga-doped ZnO(GZO) seed layer by a hydrothermal method. GZO seed layers were obtained via sol-gel technology with Ga concentration in the range of 0-4 at.%. Results indicate that the average diameter and density of ZnO nanorod arrays decrease with increasing Ga concentration, but their length shows an opposite trend.(2) The dye sensitized solar cells(DSSCs) using ZnO nanorod arrays as the photoanode layers were assembled. The photocurrent density-voltage(J-V) characteristics reveal that the DSSCs with GZO seed layer exhibit significantly improved photovoltaic performance. The dye loading, EQE and EIS analysis indicated that the performance enhancement of DSSCs based on GZO seed layer can be attributed to higher amount of dye loading, more efficient electron transportation and better electrons collection efficiency.(3) The as-prepared ZnO nanoroads with content of 0.0-0.20 at.% were mixed into ZnO nanoparticles, and employed to prepare composite photoanode for DSSCs. The obtained result shows that the energy conversion efficiency(η) increases gradually with the ZnO nanorods content rising initially, but then began to decreases. The highest energy conversion efficiency of 3.80% can be achieved in a DSSC with 0.15 at.% ZnO nanorods, which is increased by 28.4% compared with that of the pure DSSC. EIS result shows that 1D ZnO nanorods can provide a direct pathway for electron transportation and suppress the charge recombination, thus enhance the rate of electron transport.(4) Ultralong and highly crystalline rhombohedral Bi2Te3 nanotubes were fabricated by a two-step solution phase reaction. The formation of the Bi2Te3 nanotubes is attributed to the Kirkendall effect. The average length and diameter of as-prepared Bi2Te3 nanotubes are about 1~2 μm and 50 nm respectively, and the thickness is about 15 nm.(5) A novel photoanode architecture has been fabricated by embedding 0-2.5 wt.% Bi2Te3 nanotubes into ZnO nanoparticles.The photocurrent density-voltage(J-V) characteristics reveal that the DSSCs with Bi2Te3/ZnO composite photoanode exhibit significantly enhanced photovoltaic performance. The obtained result also indicates that the energy conversion efficiency(η) increases gradually with the Bi2Te3 nanotubes content rising initially, but then began to decreases. Notably, the DSSC incorporating 1.5 wt.% Bi2Te3 in the ZnO photoanode demonstrates an energy conversion efficiency(η) of 4.27%, which is 44.3% higher than that of the bare ZnO photoanode. The electrochemical impedance spectroscopy(EIS) analysis shows that the Bi2Te3 nanotubes can provide a direct pathway for electron transportation, prolong the lifetime of electron, suppress the charge recombination, and improve the electron collection efficiency. The thermoelectric effect analysis reveals that with the increase of irradiation time, Bi2Te3/ZnO composite photoanode could convert both heat and photon energies to electrical energy simultaneously and slow down the decline of η. These results suggest that compositing 1 D thermoelectric nano-materials in photoanode is a promising route to improve the performance of DSSCs. |
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