| When the organic dyes with strong absorption ability were combined on the wide band gap semiconductor surface, the spectral response of system was extended to the visible, even the near infrared region, so we called this phenomenon as “semiconductor dye-sensitized”, and the solar cell was called as “dye-sensitized solar cells(DSSCs)”. Compared with the traditional first-generation and second-generation solar technology, the dye-sensitized solar cells have the clear advantage in low-cost, light weight, flexibility, transparency, multi-color, etc, it was considered as the promising third generation of the solar cell to replace the traditional silicon-based solar cells. In order to improve the photoelectric conversion efficiency of DSSCs, the nanocrystalline porous electrode with the huge surface area for the adsorption of photosensitive dyes was required to improve the efficiency of light capture. Previously, the anatase Ti O2 fabricated by hydrothermal synthesis was the ideal material for the nanocrystalline porous electrode, excepting for the complicated hydrolysis reaction and crystallization in water with high temperature and pressure condition, which was not suitable for large scale productions due to the high cost and long production cycle. In this paper, we will take another way to fabricate the Ti O2 nanocrystalline porous electrode from commercially P25 powder, which can avoid the synthesis process of Ti O2 nanocrystalline. We researched the effects on the photovoltaic performance of dye-sensitized solar cells by the chemical dispersion, anatase phase separation, and surface passivation technology.Effects on the photovoltaic performance of dye-sensitized solar cells by the chemical dispersion technology. The P25 powder includes lots of soft aggregations with the size from hundreds of nanometers to several microns. The soft aggregations often induced the stress concentration, caused the cracks and peeled from the substrates. The large size particle aggregations was easy to produce large pores in electrode, which was not suitble to dye adsorption and charge collection. The essence of soft aggregates is van der waals attraction between the nanoparticles. In order to inhibit the attraction, we prepared to adsorb the acetic acid molecular on Ti O2 surface, which can ionizate in water and form the double electric layer on the particles, and generated electrostatic repulsion to offset the van der waals attraction and achieved the chemical dispersion by itself. The research result showed that the Zeta potential of nanoparticles in water increases from +5.35 to +46.1m V after the acetic acid adsorption, and the size of aggregations descreased from 400 nm to 30 nm. Finanly, the monodispersion P25 powder was achieved. Then, we used the CH3COO-/Ti O2 powder to fabricate porous electrodes and annealed at 500 ℃,and tested the porosity of eletrodes. Compared with the P25 electrodes, the specific surface area of CH3COO-/Ti O2 electrodes decreased from 47.16 to 44.52 m2/g, the average pore size decreased from 37.40 to 19.81 nm, and the density increased from 0.113 to 0.163 mg/cm2.μm1, the roughness factor increased 36%. We used the porous electrodes to assemble dye-sensitized solar cells and measured the photovoltaic performance. As the dispersion quality of P25 powder get better, the cell’s open circuit voltage remained the same, the fill factor slightly decreased, but the short circuit current density greatly increased from 11.8 m A/cm2 to 15.7m A/cm2, and ultimately enable the cell’s conversion efficiency increased from 6.15% to 8.07%. The enhancement of short circuit current can be contributed to the improvement of roughness factor, which characteristiced the mount of dyes per unit volume.Effects on the photovoltaic performance of dye-sensitized solar cells by the anatase seperation. The P25 powder is consisted of 80% anatase phase with the particle size of 20 nm and 20% rutile phase with the particle size of 50 nm. The anatase phase had the better dye adsorption and quicker electron transfer rate, which decided the anatase phase was more suitable to be applied in dye-sensitized solar cells. Therefore, in order to improve the photovoltaic performance of dye-sensitized solar cells fabricated from P25 powder, we should abandoned the rutile phase from the P25 powder. Due to the larger particle size and less hydroxyl functional groups on the rutile phase, when the P25 was dispersed in water, the double eletric layer on the rutile phase was more weaken than the anatase phase, which was easier to be destroyed by the ions ionized from the strong electrolyte. Without the electrostatic repulsion the rutile particles will be reunited and precipitated from the solution. XRD result showed that, as the amount of strong electrolyte increased, the strength of rutile diffraction peak became weaken, and finally dispeared, while the content of anatase phase increased from 83.2% to 100%. The porosity of powder result showed that, as the content of rutile phase reduced, the particle size decreased from 28.3nm to 19.7nm, the specific surface area increased from 49.9 to 76.3 m2/g. The separated anatase powder was used to fabricate the dye-sensitized solar cells. The short circuit current density of cells increased from 16.1 m A/cm2 to 18.2 m A/cm2, the filling factor is increased from 71.1% to 74.2%, the conversion efficiency increases from 8.52% to 10.1%. The enhancement of short circuit current and filling factor could be contributed to the larger specific surface area and quiker electron transfer rate of anatase phase. The phase composition, particle dispersion and specific surface area showed the seperated anatase powder belonged to ideal anode material. This technology can replace the hydrothermal method to fabricate Ti O2 nanocrystalline and reduced the production cost and cycle.Effects on the photovoltaic performance of dye-sensitized solar cells by the surface passivation. Although the porous nanocrystalline Ti O2 electrodes supplied huge specific surface area to adsorb great dyes, it also increased the recombination probability of electrons in conduction band with electrolyte. We decided to use surface passivated layer on the porous electrodes to inhibit the combination process and improve the open circuit voltage. Meanwhile, we considered the acceleration attenuation problem after the cells were damped. 3A molecules sieve was used as dehydration and surface passivation layer on the Ti O2 electrode to improve the open circuit voltage and long-term stability of dye-sensitized solar cells. 3A molecular sieve was aluminum silicate crystals, which belonged to the insulator material, and be coated on the electrode surface to isolate the surface electron with electrolytes. Moreover, 3A molecular sieve was metallic oxide and aluminosilicates, which combined with oxygen atoms to produce a three-dimensional interconnecting cage-like structure with lots of 3? pores and selectively adsorbed the polar water molecule from electrolyte. The research result showed that the 3μm 3A molecular sieve layer could increase the recombination resistance of cells from 79.8Ω to 95.4Ω, the open circuit voltage increased from 775 m V to 793 m V, while the short-circuit current and fill factor remained the same. Secondly, the water resistance measurement showed that the molecular sieve layer could diminished the influence of 2 wt.% water in electrolyte and kept the efficiency over 10%. |
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