Investigation On Metal-free Organic Dyes For DSSC Devices

Dye is an important component of dye sensitized cells (DSSC), because it plays a key role onthe photoelectric conversion efficiency of DSSC. In recent years, with the fast development ofDSSC, the dye is becoming one of the hot topics of DSSC research. Currently, dyes of heavy metalcomplexes are the mainstream photo sensitizers in DSSC devices due to their high device efficiency.However, metals inside the dyes are rare elements in nature, thus material supply is extremelyinsufficient for mass production. Metal-free organic dyes have many merits, such as abundant innature, tunable in molecular structure, easy purification and low environmental pollution, which ispromising to DSSC application. At present, the performance of DSSCs based on metal-free organicdyes can’t meet the requirement for commercialization, demanding further development both inaspects of efficiency and stability.This thesis focuses on the investigation of metal-free organic photosensitizer of DSSC, andfurther explores the relationship of device performance and material structure. There are mainlythree parts in our work:(1) Design, synthesis and characterization of dyes. In this part, the four target products, i.e.(Z)-3-(5-(4-((9H-carbazol-9-yl)methyl)phenyl)thiophen-2-yl)-2-cyanoacrylicacid (CBR),(Z)-3-(5-(4-(9H-carbazol-9-yl)phenyl) thiophen-2-yl)-2-cyano acrylic acid (CI),(Z)-3-(8,9-bis(decyloxy)-5-(9-(2-(2-methoxyethoxy)ethyl)-9H-carbazol-3-yl)naphtho[1,2-b:4,3-b’]dithiophen-2-yl)-2-cyanoacrylic acid (CNDT1) and(E)-2-cyano-3-(5-(9-decyl-9H-carbazol-3-yl)-8,9-bis(decyloxy)naphtho[1,2-b:4,3-b’]dithiophen-2-yl)acrylic acid（CNDT2）, were prepared by chemical bonding of different potential functional groupsand using various types of reactions. Then the structure of dyes, including intermediate of them,were characterized by1H-NMR,13C-NMR, IR and HRMS.(2) Investigation on DSSC devices based on CBR and CI. CBR and CI are two new D-π-Atype metal-free organic dyes with carbazole as electron-donor, phenylthiophene as π-conjugatedbridge and2-cyanoacrylic acid as electron-acceptor and anchor group. They were used assensitizers for DSSCs with TiO2anode prepared by electrospray method. The study of this partincludes the optophysical property, dye loading, single dye based DSSC device, and devices basedon co-sensitized dyes by combining one new dye and the conventional dye N719. Device physics were discussed as well.(3) Investigation on DSSC devices based on CNDT1and CNDT2. CNDT1and CNDT2aretwo new D-π-A type metal-free organic dyes, with carbazole as electron-donor, high conjugatedNDT as π-conjugated bridge and2-cyanoacrylic acid as electron-acceptor and anchor group. In thispart, the optical property, stability and device performance as well as the alternative-currentimpedance of these two dyes were investigated. Finally, quantum chesmistry calculation wasperformed to disclose the relationship between molecular structure and material properties.