The Photoelectric Performance Of Dye-sensitized Solar Cells Based On Photosynthetic Units From Diatom And Purple Bacteria

Dye-sensitized solar cells(DSSC) have attracted considerable attention due to its ease of fabrication, low production costs, architectural and environmental compatibility. The dye playing a role in harnessing the light energy and the nanosemiconductor being responsible for transportation of charge, are imperative components of DSSC. Natural dyes which are abundant, cost-effective and eco-friendly, have a great potential. The Ti O2 nanoparticles has some limitations as semiconductor, and improving the structure and components of semiconductor are the methods of enhancing performance of DSSC. Photosynthetic pigments and pigment-protein complexes(PPC) from diatom and purple bacteria have complementary spectra, with the main absorption in visible and near-infrared region respectively. The diatom frustules possess a remarkably organized and hierarchical porous exoskeleton, which is a photoelectric material designed by nature for scattering and trapping light. It is very important to construct an efficient and natural DSSC with visible and near infrared light response, if the photosynthetic pigments or PPC from two organisms are combined with the nanosemiconductor electrode comprising of diatom frustules. In this research, variety pigments and PPC were got from purple bacteria and diatom which was the source of diatom frustules, and frustules-Ti O2 composites were made. Then photosynthetic pigments and PPC with excellent photoelectric properties were screened. After optimization of sensitizers concentration, the absorption ways and time of co-sensitization, the structure of photoanode, the mass ratio and thickness of frustules-Ti O2 film, the spectral response region was broaden and the performance of DSSC was improved. The main results are as follows:1. The pigments and PPC sensitized Ti O2 film electrodes. After extraction,isolation and purification, six pigments and eight PPC with variety spectrum characteristics from diatom NA56 and purple bacteria CQV97 were got. The results showed that under simulated sunlight intensity of 100 m W/cm2, diatom NA56 and purple bacteria CQV97 pigment extracts had better photoelectric performance thanother pigments of diatom and purple bacteria respectively, as well as NA56 30% and CQV97 80% gradient salting aerosols showed better photoelectric performance than other pigment-protein complexes of diatom and purple bacteria respectively. NA56 pigment extracts and 30% gradient salting aerosols exhibited highest η with 0.368%and 0.392% at Chl a concentration of 155 and 129 μg/m L, respectively, and CQV97 pigment extracts and 80% gradient salting aerosols had highest η with 0.417% and0.415% at BChl a concentration of 144 and 81 μg/m L, respectively. Co-sensitization of stepwise approach showed better photoelectric performance than cocktail approach.After the Ti O2 films were immersed in NA56 pigment extracts for 12 h, then in CQV97 pigment extracts for 12 h, the highest efficiency 0.795% was made,exceeding efficiency of single pigment extracts by 114% and 90%. After the Ti O2 films were immersed in NA56 30% gradient salting aerosols for 48 h, then in CQV9780% gradient salting aerosols for 24 h, the highest efficiency reached up to 0.544%,exceeding efficiency of single pigment extracts by 39% and 31%. Co-sensitization of CQV97 pigment extracts and synthetic dye N719 enhanced current density by 36.8%compared with N719 sensitized solar cells, greatly improving the performance of DSSC.2. Preparation and characteristics of diatom frustules and frustules-Ti O2 composites. The SEM image showed that diatom frustules possessed porous exoskeleton, with pore diameters ranging from 50 nm to 200 nm. IR and Uv-vis spectrum exhibited that frustules composed of Si-O-Si bond, with absorption mainly in ultraviolet region and baking at 450℃ for 30 min didn’t damage the bonds and structure of its. Frustules-Ti O2 composites with different mass ratio were successfully made through hydrothermal method, and frustules combined with Ti O2 displayed rough surface and high specific surface area. The XRD image of frustules-Ti O2 composites exhibited that addition of frustules didn’t change Ti O2 crystal configuration.3. The pigments and PPC sensitized frustules-Ti O2 film electrodes. Double layers composed of Ti O2 and frustules-Ti O2 films showed better photoelectric performance than single layer comprised of frustules-Ti O2 film. When the double layer film was 14 μm and the second film mass ratio of frustules and Ti O2 was 12:5,we got highest efficiency. N719 and different pigments sensitized double layers film(TF3) optimized enhanced efficiency ranging from 32% to 42% compared with double Ti O2 layers film(TT), and PPC sensitized TF3 film enhanced efficiency ranging from 15% to 19% compared with TT film. The η of NA56 and CQV97 pigment extracts co-sensitized TF3 film reached up to 1.321%, enhancing efficiency by 32% compared with co-sensitized TT film, enhancing efficiency by 154% and92% compared with single pigment extracts sensitized TT film respectively, which was higher than majority of natural dyes sensitized solar cells reported.The η of NA56 30% and CQV97 80% gradient salting aerosols co-sensitized TF3 film reached up to 0.712%, enhancing efficiency by 19% compared with co-sensitized TT film,enhancing efficiency by 84% and 35% compared with single PPC sensitized TT film respectively, which was higher than PPC of algaes and purple bacteria sensitized solar cells reported. Thus, the photosynthetic pigments or PPC of diatom and purple bacteria co-sensitized film electrodes incorporating frustules, significantly improving performance of solar cells sensitized by natural dyes.