Design, Synthesis And Study On The Properties Of Organic Photovoltaic Materials Containing Triphenylamine And Thiophene

The research progress of the materials and devices of organic solar cells were summarized systematically in this dissertation. In specially, the current developments of the conjugated polymer electro-donor materials and organic photo-sensitizers used in organic solar cells were introduced in detail. The absorption spectra, hole mobility and solubility of organic photovoltaic donor materials are the major factors to affect the power conversion efficiency (PCE) of organic solar cells. This dissertation is focusing on the design and synthesis of series of new poly(p-phenylenevinylene) (PPV) derivatives with conjugated side chain which have broader absorption band, higher hole mobility and better solubility for improving the photovoltaic properties of the conjugated polymers. At the same time, we designed and synthesized a series of donor-p-acceptor (D-p-A) metal-free organic dyes which were applied in dye-sensitized solar cells (DSSCs). The structure of the as-synthesized compounds were proved and confirmed by FT-IR, ¹H NMR, ¹³C NMR and element analyst. The photophysical, electrochemical and photovoltaic properties of the copolymers and dyes have been extensively studied by UV-vis absorption spectra, photoluminescence spectra and cyclic voltammograms. We also investigated the PCE of the solar cells based on as-synthesized copolymers and metal-free organic dyes. The main study results are listed below:1. Two novel PPV derivatives P1 and P2 with triphenylamine moiety directly attached as side group were designed and synthesized by the Wittig-Horner reaction. The effects of the triphenylamine side group on the thermal stabilities, optical absorption, electrochemical and photovoltaic properties of the copolymers were investigated thorough. The study results indicate that 3D p-p stacking structure of triphenylamine side chain plays an important role on enhancing the thermal stability, improving the hole mobility and photovoltaic performance of the copolymers. The PCEs of the bulk heterojunction polymer photovoltaic cells based on P1 and P2 reached 0.27% and 0.45% under the illumination of AM 1.5 (90 mW/cm²), respectively, which were 3 and 5 times higher than that of the device based on P0 (0.09%) without triphenylamine side chains.2. Three new PPV derivatives with conjugated mono- or di(thiophenyl) side chains, P3, P4 and P5, were designed and synthesized by the Wittig-Horner polymerization method. The thermal stabilities, photophysical, electrochemical, and photovoltaic properties of the copolymers were investigated in detail. The results show that the conjugated side chains have obvious influences on the thermal stability, band gap, solubility and photovoltaic performance of the copolymers. The dye-sensitized solar cells (DSSCs) based on P3, P4 or P5/TiO₂ showed PCEs up to 1.66%, 1.05% and 2.56% under the illumination of AM 1.5, 100 mW/cm², respectively.3. Three tercopolymers of P4-BO20, P4-BO30 and P4-BO40 were designed and synthesized to solve the problems of the copolymers P4 in solubility and absorption spectrum by introducing the compound of Monomer 5. We found that the thermal stabilities, absorption bands and band gaps of the tercopolymers of P4-BO series could be tuned up well though modulating the ratio of Monomer 5 in the main chain. For P4-BO series, a tercopolymer/TiO₂ DSSC based on P4-BO20 which contain Monomer 5 of 44% gived the maximum PCEs of 1.76%.4. By introducing the compound of Monomer 1, three tercopolymers of P5-TPA20, P5-TPA25 and P5-TPA30 were also designed and synthesized to overcome the disadvantages of copolymers P5 in norrow absorption spectra and low hole mobility. We found that the ratio of Monomer 1 with the triphenylamine conjugated side chain in the main chain had an important effect on the injection of hole, charge transfer and photovoltaic performanc of the tercopolymers of P5-TPA series. For P5-TPA30 series, a DSSC based on P5-TPA25 which contain Monomer 1 of 52% gived the maximum PCEs of 2.74%.5. A series of organic D-p-A dyes (SD1～SD5) comprising triphenylamine (TPA) moieties as the electron donor, cyanoacetic acid moieties as the electron acceptor/anchoring groups and thiophene-bridge with/without n-hexyl-substituted as p-conjugated units, were designed, synthesized and applied in DSSCs. Effects of the length of p-conjugated unit and the alkyl chain on the photophysical, electrochemical and photovoltaic properties of dyes had been extensively studied. It was found that a suitable p-conjugated length should be adapted to the dye structure for a better PCE value and the hexyl chain could improve the short-circuit photocurrent density (I_sc), open-circuit photovoltage (V_oc) remarkably, which result in relative high PCE value. In EtOH solution, a DSSC based on SD2 with one hexyl-substituted thiophene as p-conjugation unit exhibited the maximum PCE of 6.22% under simulated AM 1.5 G solar irradiation (100 mW/cm²), which approached 88 percent conversion efficiency of an N719-sensitized device (7.07%) fabricated and measured under similar conditions. The results suggest that as a new dye SD2 is a promising high efficient and low cost organic dyes used in DSSCs.