Synthesis And Properties Of D-A-D Type Organic Small Molecular Photovoltaic Materials

Solution-processable bulk-heterojunction organic solar cells have attracted great attentions because of their cheap production cost, easy fabrication and large-scale manufacture potential. In the selection of organic photovoltaic materials, despite that polymers achieve high power conversion efficiency, researchers recently focus on small molecular materials for their simple structure, well reproduction, facile purification, and so forth. In addition, donor-acceptor (D-A) conjugated organic materials catch the eyes, because this structure not only reduce the band-gap to broaden molecular absorbance range, but also investigate the relationship between various functional groups and properties of materials.In this article, a series of D-A-D type organic small molecular photovoltaic materials for organic solar cells have been designed, which contain benzothiadiazole or diketopyrrolopyrrole as acceptor and triphenylamine or N,N-dimethylaniline as donor. In addition, aliphatic side-chains are considered to increase molecular solubility and cyano is introduced on the conjugated bridge bonds. Density functional theory calculations were needed for designed compounds to understand the their properties at molecular level. In order to obtain their photophysical and electrochemical nature, UV-vis absorbance spectrometry and cyclic voltammetry test were carried out on these materials. Additionally, fluorescence quenching experiment with PC61BM were applied on synthesized compounds for the purpose of detecting photoinduced charge separation. The solution-processable organic solar cells with synthesized molecules as donor and PC61BM as acceptor were fabricated and measured.Based on the performances of synthesized materials, this dissertation discussed how triphenylamine and N,N-dimethylaniline affect photovoltaic properties, compared the electron withdrawing effect between benzothiadiazole and diketopyrrolopyrrole, analyzed results of aliphatic side-chains on molecular planarity, and evaluated influence of cyano acting on energy levels. This work investigates the relationship between structure and properties for organic small molecular photovoltaic materials from donor/acceptor unit, aliphatic chain and bridge band, which is of great value to photovoltaic materials design.