Design, Syntheses And Performance Of Two-Photon Absorption Complexes And Polymeric Solar Cell Materials

Two-photon absorption (TPA) effect is one of the third-order nonlinear optical properties. The study toward organic TPA materials is a forefront topic of non-linear materials, and has very important application prospects. The development of solar cell is an efficient way of collecting the abundant solar energy, of which polymer solar cell becomes a new research topic due to its potential advantages. Despite their different intrinsic physical mechanisms and various application scopes, both of them belong to organic optoelectronic material. Especially from the view point of chemistry, their molecules are both of large π-electron conjugated systems. Therefore, in this thesis, we conduct investigation on these materials with similar molecular structure characteristics.This thesis contains two parts. The first part (Chapter2～6) concerns the molecular design, synthesis, structure and photophysical properties of novel organic third-order NLO materials, with an emphasis on the TPA properties of M-Salen coordination compounds. We hope to investigate the relationship between chemical structures and their TPA properties of these coordination compounds, and as well to explore novel organic TPA materials with high cross sections. The second part (Chapter7and8) concerns molecular design and synthesis, of novel organic conjugated donor materials incorporating donor-acceptor (D-A) structures in main chain, or both in main chain and side chain, and afterwards the study toward the performance of bulk-heterojunction PSCs devices fabricated using these polymer donor materials. The main contents of the thesis are as the following.Chapter1introduces the basic concepts of the third-order nonlinear optical effects and the construction of organic solar cells, and then briefly reviews the research progress of organic TPA materials and bulk-heterojunction PSCs, as well as the investigation of the structure-property relationships. The design strategies and main contents of the thesis are outlined.In chapter2, we designed and synthesized a series of Ni-Salen and Cu-Salen complexes with different push-pull groups. Their chemical structures are fully characterized. Their third-order NLO properties are measured using the ND-2PA method. The results indicate that complexes with strong electron donating/withdrawing groups exhibited two-photon absorption effects. This study provides useful information for our following work.In chapter3, on the basis of the above work, a series of new metal (Cu2+and Ni2+, respectively) complexes of Salen ligands are designed, synthesized and structurally characterized. Their TPA properties are measured by ND-2PA and Z-scan technique. The results suggest that all complexes exhibited different magnitudes of two-photon absorption, while the TPA cross section values (σ2) of some complexes which have large conjugated system are greater than3000GM. The effects of molecular structure to TPA properties has been analyzed and discussed. The study shows that these complexes are all potential materials for TPA materials.In chapter4, we have designed and synthesized a series of thiophene derivative containing salicylaldehyde and their corresponding coordination compounds with Cu2+or Ni2+ions. Their structures were characterized and both single-photon and two-photon absorption properties of them were studied. The σ2of complex S-29having2,2’:5’,2"-terthiophene unit in the structure is around2000GM. The effects of molecular structure on the linear and nonlinear optical properties are discussed in detail.In chapter5, we have designed, synthesized and structurally characterized a series of M-Salen complexes where carbon-carbon single bond, double bond or triple bond serves as conjugated bridge in the molecular structures. Their TPA properties are measured with ND-2PA and Z-scan technique. The results show that the σ2of three complexes are exceeding1000GM, and the largest σ2value is1935GM. We discussed on the linear/nonlinear properties optical properties of these complexes, and investigate their structure-property relationships.In chapter6, we have designed and synthesized a series of A’-π-A-π-A’ or D-π-A-π-D type M-Salen complexes in which4-nitrobenzene, ferrocene or carbazole unit serves as the terminal groups, respectively. Their structures have been characterized and their photophysical properties studied. The TPA property has been studied with both ND-2PA and Z-scan technique. The effects of metal coordination and different terminal groups on the linear and nonlinear optical properties are discussed in detais. In chapter7, three D-A type copolymers containing isoindigo or DPP as the acceptor unit and the benzodithiophene, bisthiophene-dithieno[3,2-b:2’,3’-d]-pyrrole or alkylidene fluorine as the donor unit have been designed and synthesized by the Pd-catalyzed Stille-coupling reaction. Their structures have been characterized and their thermal stability, optical and electrochemical properties have been studied. Then, we manufactured their BHJ PSCs devices and measured their performances. The factors affecting the solar cell performances (including the structure-property relationship, the energy band, UV absorption spectra and the film formation ability) are discussed.In chapter8, novel alternating copolymers were designed and synthesized, with DPP unit and triphenylamine (carbazole) group copolymerized in the main chain, or introducing strong electron acceptor malononitrile unit on the triphenylamine (carbazol) unit to get conjugated side chain. The structures are fully characterized, the photovoltaic and electrochemical properties and thermal stabilities are measured. The alternating copolymers are applied as donor materials in bulk-heterojunction PSCs devices, and the structure-property relationship are discussed.