Synthesis And Photovoltaic Properties Of Conjugated Organic Molecules Based On Alkoxy Sustitutied Benzodithiophene And Spiro(Cyclopentadithiophenefluorene)

In recent years organic/polymer solar cells developed quickly, of which the organic donor materials is one of the most important parts. The design, synthesis and photoelectric properties of D-A type conjugated polymers and A-D-A type small molecules are the focus in organic solar cells research field. Aiming to obtaining high efficiency organic/polymer donor materials, we synthesize a series of D-A type polymers based BDT and three types of A-D-A small molecules based on a spiro central unit. The absorption spectra, electrochemical, and photovoltaic performance of these materials are described in detail in the main text. The main research work as follows:1. We designed and synthesized the new electron-donating unit(BDTOT) which consists of a BDT backbone with conjugated 2-(2-ethylhexyl)-3,4-dimetho xythiophene side chains. By alternating copolymerization of BDTOT with electron-accepting units(fluorinated benzothiadiazole(FBT), benzothiadiazole(BT) and pyrrolo[3,4-c]pyrrole-1,4-dione(DPP)) three donor-acceptor(D-A) copolymers(PBDTOT-FBT, PBDTOT-BT, and PBDTOT-DPP) were developed for PSC applications. The impact of dimethoxythiophene substituent and the electron-accepting strength of the acceptor units on the absorption, HOMO/LUMO energy leVels and photovoltaic properties of the polymers was investigated in detail. Our research shows that 3,4-dimethoxy thiophene can increase the electronic ability of BDT unit which is helpful to obtain a wider absorption spectrum, meanwhile maintain a low HOMO energy. These advantages are conducive to get a high PCE. The PCE of PBDTOT-FBT, PBDTOT-BT, and PBDTOT-DPP are 4.48%?2.47%?3.05%, respectively?2. We designed and synthesized three electron-donating units of BDT-DMT, BDT-MT and BDT-ET, which consists of a BDT unit with 3,4-dimethoxyl thiophene, 3-methoxyl thiophene, and 3,4-ethylenedioxyl thiophene side chains, respectively. Copolymerization of BDT-DMT, BDT-MT and BDT-ET with electron-accepting units of fluorinated benzothiadiazole(FBT), three donor-acceptor(D-A) copolymers(PDMT-FBT, PMT-FBT and PET-FBT) were developed. The influence of molecular configuration, absorption spectrum, electrochemical, and photovoltaic performance by alkoxy substituents are investigated in detail. The results show that, alkoxy substituents can increasing the molecular steric hindrance, result in a slight blue shift of absorption spectrum and a significant decreasing the HOMO energy level. In a word, the introduction of alkoxyl substituents are beneficial to improving PCE. The PCE of PDMT-FBT, PMT-BT, and PET-DPP are 4.48%?3.29%?2.40%, respectively?3. We designed and synthesized three A-?-D-?-A small molecules, which contain a new spiro 2',7'-di-tert-butylspiro[cyclopenta[1,2-b:5,4-b']dithiophene-4,9'-fluorene](SF) central unit(D), three differernt electron-withdrawing acceptors YT, RDN and RCN(A) and terthienyl ?-bridge. The impacts of central unit and acceptor unit on the absorption spectrum, electrochemical and photovoltaic properties of the three small molecules are investigated. Our research shows that the spiro central unit can bring down HOMO level and improve the molecular accumulation state in some extent thus improve the JSC and FF; while the electron-withdrawing A unit also has an obvisous effect on the photovoltaic performance of the materials. We can well control the photophysical, electrochemical properties and photovoltaic performance of the molecules by choosing different A. The PCE of SFYT,SFRDN and SFRCN are 6.68%, 3.30% and 4.33%, respectively?...