Synthesis And Properties Of DPP Based Organic Small Molecular Photovoltaic Materials

Organic small molecular solar cells have attracted great attention for their advantages of low cost, flexibility and easy-synthesis. Rencently, bulk heterojunction (BHJ) structure was widely studied in recent years because this structure can significantly enlarge the donor/acceptor interface and improve the photovoltaic performance. In order to introduce small molecular semiconductors into commercial solar cells, the manufacture cost need to be reduced and performance need to be improved for solution-processable bulk-heterojunction small molecular solar cells.Rencently, acceptor-acceptor (A-A) or donor-acceptor (D-A) structure connecting electron-withdrawing unit (A) and electron-donating unit (D) in organic small molecules are widely investigated. Because this design makes it possible to simutaniously efficiently improve intramolecular charge transfer (ICT) and reduce the band gap. In this dissertation, a series of A-A-A and D-A-D type organic small molecular photovoltaic materials have been designed and synthesized successfully, consisting of diketopyrrolopyrrole (DPP) as the central electron-withdrawing unit. In A-A-A type small molecules, strong electron-withdrawing unit served as terminal electron acceptor and alkylated thienyl as π conjugated bridge. In the D-A-D type small molecules, triphenylamine (TPA) served as the electron-donating unit, and phenylethylene as n conjugated bridge. In addition, the solubility of materials is expected to improve by introducing alkyl as side chain.The photophysical and electrochemical properties of these synthesized compounds were investigated by theoretical calculation (DFT), UV-vis absorption spectroscopy and cyclic voltammetry test. Density functional theory calculations were needed for designed compounds to predict their properties at molecular level. The photophysical and electrochemical properties showed that all materials exhibited broad absorption range from300nm to800nm and possess appropriate energy levels to satisfy the requirement of solution-processable BHJ devices, with PC61BM as electron acceptors. Therefore, we explored the PV properties of these synthesized donors by fabricating BHJ solar cells with a covintional structure of ITO/PEDOT:PSS/Donors:PC6]BM/Al under an illumination of AM1.5G (100mW cm-2).