Preparation Of ZnO - Based Dye - Sensitized Solar Cells By Low - Temperature Solid - Phase Method

Swedish scientists O’Regan and Gratzel successfully synthesized dye-sensitized solar cells with7.1%energy conversion efficiency via coating appropriate organic dye as sensitizer on porous nanostructures TiO2photoanode. Hereafter, plenty of research works aim at seeking, selection and preparation of photoanode; preparation and design for counter electrode; synthesis of sensitizer and selection of electrolyte. However, so far processes above did not lead to any breakthrough on improving energy conversion efficiency, especially in the researches of photoanode preparation methods such as Sol-gel, Powder Coating, Hydrothermal, Chemical Vapor Deposition (CVD), Electrochemical Process (EC) and Plasma Spray. In spite of distinctive features, many disadvantages exist in these methods. Low-heat Solid State Reaction (LHSR) method received attentions for its advantages such as energy conservation, eco-friendly, large sphere of application and facile reaction conditions. However there are rare researches on preparation of DSSC photoanode. Here we report the superiority of preparing DSSC photoanode by LHSR via analyzing the relations between the morphology and structure of as-prepared photoanode films, photovoltaic performances and preparation conditions.Our research works contains:(1). Preparing mesoporous ZnO photoanode films via LHSR:The precursors were prepared with Zn(NO3)2·6H2O, H2C2O4·2H2O, ethyl cellulose by low-heating solid state reactions (Low-heating Solid State Reaction, LHSR) method. The mesoporous nano-ZnO (MNZ) film was fabricated by spin-coating method with the powder obtained via firing the precursors at different temperature. The characterization results of XRD, SEM and BET show that a three dimensional mesoporous nano-ZnO(MNZ) films was prepared. The specific surface area of as-prepared three powder indicated the change at400,600,800℃, which reached the peak at400℃. To combine with the measurement of photoelectric properties and UV-VIS spectrum, them demonstrated that the MNZ films have two special function of optical trap and capillarity, therefore it can not only effectively improve the light scattering, but also speed up the dye adsorption rate which greatly shorten the soaking time. The relationship between film morphology and photoelectric properties were analyzed via characterizing information. The beneficial enlightenment have provided for next study of preparing MNZ films by means of LHSR method.(2). Preparing various morphology ZnO photoanode films via LHSR:Oxalic acid, hexamine and ammonium bicarbonate was mixed with zinc nitrate to conduct a Low-heat Solid State Reaction in order to prepare the precursors. Three of the as-prepared precursors with different morphologies was respectively identified as Zn5(NO3)2(OH)8)2H2O and Zns(CO3)2(OH)6through characterization. The as-prepared precursors were pulped and then knife coated into film. After calcining the film, we obtained a complex ZnO photoanode film with three types of morphologies which agreed with the morphologies of precursors including rod-like, plate-like and cluster structure. Comparisons of SEM images and thermal analysis curves between before and after calcination indicate that gas is released from precursors when they are heating to produce mesoporous in film. In addition, morphologies of thermolysis productions are inherited from precursors. This proves the precursors synthesized in room temperature play a decisive role in the formation of final productions’morphologies. Test of photovoltaic performance shows that multistage structure can increase the incident light scattering when it is composed of combination of cluster structure. What’s more, its interlaced nano flowers as the fast channel of electron transmission can improve the electron collection efficiency to the top of three types’morphologies with JSC of10.86mA·cm-2and photoelectric conversion efficiency of3.07%. This process provides a beneficial enlightenment for preparing various morphology photoanode films via LHSR in the further research.(3). Studying the influences of surfactants to plate-like ZnO based photoanode films prepared via LHSR:Based on the analysis of various morphologies ZnO based photoanode films, we added three different surfactants to control the morphologies of ZnO photoanode. We found adding PEG4000in the process of preparing precursors can obtain photoanode film with the best quality and integrity. In addition, the size of plate-like nanoparticles which form the film is500nm that is closed to the maximum absorbance peak of N719dye. All characters above lead to a photoelectric conversion efficiency of3.43%. In order to improve the photoelectric conversion efficiency of DSSC, surface modification has applied to those photoanode films prepared by precursors with surfactants. A comparison of SEM images and photovoltaic performances between before and after surface modification indicates that surface modification leads to refining the plate-like nanoparticles of ZnO photoanode films in different levels, increasing the superficial areas and improving absorbing capacity of dye. Finally we found the maximum refinement level of ZnO nanoparticles happen in the photoanode film which is composed of the biggest plate with cetyl trimethyl ammonium bromide (CTAB). This results in a biggest increase of the photoelectric conversion efficiency from2.86%to3.69%.(4). Preparation of different morphologies composite structure about ZnO phase DSSC light anode with LHSR and properties of it.Through several Doctor blade, to obtain a combined composite structure of light anode film and this film was consisting of two different morphologies of ZnO the precursor prepared with LHSR. Take advantage of the different morphologies of ZnO, it eventually manifested photoelectric conversion efficiency play a plus one is greater than two effects.(5). Preparing and researching ZnS quantum dots sensitized via solid state reaction:We successfully synthesized ZnS quantum dots in size of4nm with uniformly distributed sizes but agglomeration. Cubic crystal system structure character was observed in the as-prepared quantum dots after characterization which proves their good crystalline state. In addition, under the ultraviolet absorption spectrum, the as-prepared quantum dots displays a blue shift phenomenon depended on conditions change as well as the effect of the quantum dots color transition. Comparing with other processes to synthesize ZnS quantum dots, solid state reaction shows up advantages in reducing operation steps, decreasing preparation times, improving preparation efficiency, operating simply, saving costs and beneficial use in industry.