Research On Dye-sensitized Solar Cells Based On The Heterojunction And Conducting Polymer Counter Electrodes

Dye-sensitized solar cell （DSSC） has been one of the hot-spots in the field ofsolar cells, because of its simple fabrication process, low cost, environmentallyfriendly and high efficiency. According to the problems of key scientific andtechnicol in this filed, the research in dye-sensitized solar cell based on theheterojunction and conducting polymer counter electrodes was carried out in thispaper to improve the performance and reduce the cost of device. There are somemajor works and results in the following:In chapter1, it demonstrated the research progress of DSSCs at home and abroad.The development process, current study situation, fundamentals, charccterization andproblems of the DSSC were described emphatically, and the research purpose andsignificance of the thesis were also illustrated.In chapter2, an iodine/iodide-free and poly （3-hexylthiophene）/6,6-phenyl-C61-butyric acid methyl ester （P3HT/PCBM） heterojunction hybrid solarcell （HSC） was fabricated based on the fluorine-doped tin oxide conductive glasssubstrate （FTO）. The UV-vis spetra showed that the P3HT and PCBM as the electrondonor and acceptor materials had excellent sensitization functions. A HSC with highefficient was fabricated by using P3HT/PCBM as charge carrier transferring mediumto replace dye and I/I3redox electrolyte. Under an optimized condition withP3HT/PCBM mass ratio of1:2, the heterojunction hybrid solar cell achieved alight-to-electric energy conversion efficiency of2.97%.In chapter3, the poly （3,4-ethylenedioxythiophene）:polystyrenesulfonate（PEDOT:PSS） with high conductivity served as electron-hole transporting materialto construct a heterojunction solid-state hybrid solar cell with the structure ofFTO/PEDOT:PSS/TiO₂/PCBM:P3HT/Pt. The PEDOT:PSS film and device wereheated at120℃in vacuum environment, and the heterojunction hybrid solar cellobtained the power conversion efficience of1.90%under a simulated solar light illumination of100mW·cm^-2.In chapter4, an ultraviolet responsive hybrid solar cell based on titaniumdioxide/poly （3-octylthiophene-2,5-diyl）（TiO₂/P3OT） or TiO₂/P3HT heterojunctionwas devised. In the solar cell, TiO₂as an ultraviolet light absorber and electronicconductor, P3OT or P3HT as a hole conductor, the light-to-electric conversion wasrealized by the cooperation between these two components. It could be demonstratedby the UV-vis spectra and IPCE curves that the TiO₂film, the P3HT/TiO₂film, andthe P3OT/TiO₂film all showed wide and strong absorption in300-400nm. UnderUV light irradiation with the intensity of100mW·cm^-2, the light-to-electric energyconversion efficiency of the heterojunction hybrid solar cells with P3HT and P3OTwere1.28%and1.16%, respectively. The stabilities of solar cells based on P3HTand P3OT polymer were measured in dark and UV light soaking, and optimized theperformance of the heterojunction hybrid solar cell by doping inorganic salt in theconductive polymer solution.In chapter5, a novel CdTe quantum dots sensitized heterojunction hybrid solarcell was fabricated with Pt/C60counter electrode and TiO₂–polydimethyldiallylammonium （PDDA）-CdTe photoanode. In this solar cell, the microporous Pt/C60counter electrode was prepared by using a facile thermal decomposition method andthe TiO₂–PDDA–CdTe photoanode was prepared by using chemical bath depositionmethod. When comparing the device with different transferring medium of I/I3,S2/Sx and PCBM/P3HT, significant improvement on the power conservsionefficiency was observed in the device based on PCBM/P3HT, and resulted in a highpower conversion efficiency of3.40%under light irradiation with intensity of100mW·cm–2.In chapter6, a novel counter electrode with high conductivity and excellentelectrochemical catalytic activity for dye-sensitized solar cell was prepared bycoating PEDOT:PSS on FTO at low temperature. The experimental results showedthat DSSC obtained the optimal photoelectric performance for PEDOT:PSS/carboncounter electrode annealed at80℃under vacuum condition. The overall energyconversion efficiency of the DSSC with PEDOT:PSS/carbon counter electrode reached7.61%under a simulated solar light illumination of100mW·cm^-2. Thescanning electron microscopy （SEM） indicated that the PEDOT:PSS/carbon counterelectrode prossessed large specific surface area. It was demonstrated by the cyclicvoltammetry, resistivity and conductivity measurements that the PEDOT:PSS/carboncounter electrode illustrated excellent electrocatalytic activity in the I/I3system.In chapter7, a PEDOT:PSS/polypyrrole （PPy） composite film was preparedand employed as counter electrode in dye-sensitized solar cell by cyclicvoltammetry polymerization method. The power conversion efficiency of the DSSCbased on the PEDOT:PSS/PPy counter electrode obtained7.60%under a simulatedsolar light illumination of100mW·cm^-2. It could be inferred from the SEM that thePEDOT:PSS/PPy film was expected to possess a high effective electrochemicalsurface area and large rough surface. The electrochemical measurements showedthat the PEDOT:PSS/PPy film had a low surface resistance, high conductivity, andexcellent catalytic performance for the I/I3electrolyte.In chapter8, multi-wall carbon nanotubes decorated with tungsten sulfide（MWCNT-WS2） were synthesized by using a hydrothermal method and wasincorporated into a Pt-free DSSC system as counter electrode with doctor blademethod for the first time. Cyclic voltammetry and electrochemical impedancespectroscopy characterizations indicated that the counter electrode had a highcatalytic activity for the reduction of triiodide to iodide and a low charge transferresistance at the electrolyte–electrode interface. The influence of MWCNT contentsto the catalytic activity of counter electrode and performance of the dye-sensitizedsolar cell were discussed, and it was found that the device possessed the optimalperformance with MWCNT ratio of5wt.%. A high power conversion efficiency ofDSSC based on the counter electrode achieved6.41%under a simulated solarillumination of100mW·cm–2, and corresponding to the short-circuit current density（Jsc） of13.51mA·cm–2, the open-circuit voltage （Voc） of0.73V and the fill factor（FF） of0.65, respectively.In chapter9, it gave a summation for the major research and innovation of thethesis, and offered prospects on the future progress of the work.