Study On The Material For The Photoanodes And Counter Electrodes Of Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have quickly become a potential candidate for large-scale utilization of solar energy owing to their safety, non-toxic, potentially low cost and relatively high photoelectric conversion efficiency. The photoanodes and counter electrodes are two important components of DSSCs because the photoelectric conversion efficiency and stability of the batteries are affected by the composition and structure of them.The TiO2 nanoparticles film, the most widely applied in the photoanodes for DSSCs, is a key role for the photoelectric properties, acting as a dye loader, also having functions of photogenerated electrons reception and electron transmission. Unfortunately, there are still some problems in TiO2 films, such as high density of surface states and the lower electron mobility, which undoubtedly accelerated the charge recombination and hindered the charge transfer. In order to promote the wide application of DSSCs and explore the more efficient photoanodes, SnO2/TiO2 composite photoanodes were prepared based on the traditional commercial TiO2 (P25) photoanodes, to taking advantage of high electron mobility of SnO2. The result indicated that the electron transfer rate has been accelerated on the photoanodes, the interface optoelectronic recombination has been hindered and the charge collection efficiency has been improved. In addition, the counter electrode, another important component of DSSCs, acted an important role such as collect the external electrons, absorb electrolyte and ensure continuous tri-iodide reduction. The traditional electrode material is platinum, and its cost accounts for about 70% of the batteries. So there is an urgent need to find a substitute of Pt as CEs to reducing the cost of the batteries. In this paper, the application of composite materials of carbon and conductive polymer instead of platinum as the counter electrodes (CEs), has greatly reduced the cost of the battery.Through test the output characteristics of the short circuit current density-voltage curves (J-V curves) for DSSCs, the main factors to inpact photoelectric conversion efficiency of DSSCs were explored, and the impact mechanism were analyzed. The main contents are as follows:(1) The 10 nm TiO2 and 20 nm SnO2 nanoparticles were used as photoanodes and prepared for DSSCs respectively. By compared with P25, the parameters of performance which affect the efficiency of the DSSCs were analysized. The results showed that, there were much difference in photoelectric performance parameters between several kinds of nanoparticle semiconductor films such as specific surface area, amount of dye adsorption, open circuit voltage, short current density, and so on. Although SnO2 has caused much concern because of its high electron mobility, the pure SnO2 is not a good material for photoanodes of DSSCs.(2) Using the mixed system of TiO2 and SnO2, TiO2/SnO2 composite material was introduced to the photoanodes and the DSSCs. The high crystallinity 3.4 nm-sized SnO2 was synthesized by the hot-bubbling method. By the comparison of the composite photoanodes with different quality percentage of SnO2, it is found that when the mass percentage of SnO2 and TiO2 is 7.5, the specific surface area of the composite electrode, conductivity and charge collection efficiency all reached the maximum value. It was discussed the photoinduced electron transfer and the energy band structure of TiO2/SnO2 composite in order to study on the photoelectric properties and photoinduced electron transfer mechanism.By the four point probe conductivity test and ETS test, it was confirmed that the conductivity performance of TiO2/SnO2 composite films was excellent. Therefore, the short-circuit current density of DSSCs with TiO2/SnO2 composite is greatly improved, and the maxmum efficiency up to 6.6%, a ～52% improvement compared to TiO2.(3) The PDDA/CNTs composite, obtained through PDDA functionalized multiwalled carbon nanotubes, served as the CEs to replace the traditional high cost material Pt in order to greatly reduce the cost of the batteries. The main factors affecting the photoelectric properties and the stability of PDDA/CNTs based DSSCs were discussed. The power conversion efficiency of the optimized DSSCs and incident photo-to-electron efficiency (IPCE) reached 5.65% and 61.6% respectively. Relative to CEs of the pure CNTs, the optical performance of DSSCs is significantly improved, mainly due to the fact that CNTs has strong conductivity and PDDA/CNTs composites show more excellent catalytic activity in the oxidation redox reaction. The PDDA/CNTs composite is an excellent potential substitute to Pt as the CEs in DSSCs. This method of low temperature synthesis of carbon nanotube-conductive polymer composites, provides a valuable reference for the future research work on the new materials in CEs.(4) Explore simple, effective way for preparation the CEs slurry and the coating methods for the films on FTO glass substrates. Without adding any binder or surface active agent, the slurry of CNTs and PDDA/CNTs composite materials for the CEs by using deionized water as the solvent. To obtain the films, the simple dropping method and low temperature drying method were introduced. It was found that the efficiency of cells were almost the same by comparing the two methods of spin coating and dropping to prepare the films. The dropping method can also be used for slurry of platinum. The dropping way and low temperature drying method for the CEs, have many superiorities such as simple and easy to operate, easy to control the film thickness, and uniformity films. That provides an effective reference for prepare CEs with carbon material and conductive composit.