Design, Synthesis And Optoelectronic Properties Of Novel Organic Small Molecules And Conjugated Polymers

Organic semiconducting polymers have attracted extensive research and industrial interest since they were discovered in 1976, after that they began to be applied in some new areas such as organic small molecule and polymer solar cells(PSC), etc.Organic small molecule and polymer solar cells have gained much attention due to their advantages of of lightweight, flexibility and being solution processable for large-area devices. Since 2003, scientists have made tremendous progress in aspects of design and synthesis of the novel active layer materials, exploring the working mechanism of OPVs, optimization of the active layer morphology using all kinds of methods, innovation of the device structure type and interface modification engineering, and the large-scale production process and stability of the device. On the basis of these findings, it was reported in the literature that OPVs single junction devices with power conversion efficiency(PCE) over 10.8% have been achieved. However, in numerous work in improving the PCE of OPVs, developing active layer materials is the most basic research. Therefore, how to design and synthesis a series of new organic small organic molecules and conjugated polymers for the active layer materials of solar cells through chemical synthesis method is unceasing exploring research of every chemical researcher. This dissertation aims to assemble, optimize and regulate some common building blocks of active layer materials for organic solar cells, in order to develop a series of novel small organic molecules and conjugated polymers through novel chemical synthesis method. Meanwhile, we study the relationship between changes in the chemical structure and the photovoltaic device performance in detail, providing an important reference for the future design of new materials and it is of great significance.Triphenylamine small molecule is an important system in the current structure system of the active layer materials for small organic molecule solar cells. Triphenylamine small molecule possesss advantages of simple chemical synthesis, cheap raw materials, and post chemically modification. Therefore, in chapter two we designed and synthesized a series of small molecules based on triphenylamine, breaking the symmetry of the triphenylamine molecule through introducing different degrees of electron-withdrawing units, thus combining the different ICT absorption bands to broaden absorption spectrum. Through this work, we put forward the concept of the three-dimensional asymmetry of the triphenylamine molecule, introducing three different degrees of electron-withdrawing units in the same triphenylamine molecule. Meanwhile, we creatively synthesized a new electron-withdrawing unit. Although the final device performance based on asymmetry triphenylamine molecule is not very satisfactory, this molecular design concept has far-reaching significance in brodening the absorption spectrum, in order to better capture sunlight.In chapter three we studied another hot topic of the structure system of the active layer materials for small organic molecule solar cells–oligomers in detail. We applied the "one-pot" synthetic method in organic small molecule solar cells, synthesizing two kinds of oligomers, amorphous or semi-crystalline. Their thermal, optical, electrical, and carrier transport properties, as well as the performance of photovoltaic devices based on these oligomers have been systematically studied. In addition, a detailed structural analysis of these oligomers in the bulk hetero junction films was performed using by atomic force microscopy(AFM), grazing incidence X-ray diffraction(GIXD) to elucidate the influence of molecular structure of the oligomer on the morphology of the active layer. These studies have important significance for our future design and synthesis donor materials of the active layers for small organic molecule solar cells. Amorphous polymers can transport charges along their long polymer backbones and achieve high carrier mobility, thereby obtaining optimum photovoltaic performance. However, for small molecules, they must have high crystallinity because of their short molecular chains, so that the effective charge transport along the π-π stacking between molecules direction, thereby enhancing the hole mobility and photovoltaic properties.In chapter four we turned our research focus from small organic molecules to polymers. The polymers we studied are different from traditional D-A polymers and are a kind of acceptor-pended conjugated polymers. We introduced naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole(NT), a building block that consists of two 1,2,5-thiadiazole fused rings, into the polymer side chains and utilized its enlarged planarity and stronger electron-withdrawing capability to expand the absorption spectrum of the polymer, optimize energy level structure of the polymer and enhance charge-carrier mobility, thereby improving photovoltaic performance. Through this work, we enriched and developed the acceptor-pended conjugated polymers system and also proved double application value of the NT unit in linear polymers and acceptor-pended conjugated polymers.In chapter five we further studied another hot topic of polymer materials system —D-A1-D-A2 type polymers. In order to develop D-A1-D-A2 polymers with near-infrared absorption, we introduced diketopyrrolopyrrole(DPP) unit into polymers, designed and synthesized five kinds of D-A1-D-A2 polymer and studied the effect of conjugated polymer donor chain length on the optical properties, electrical properties, the energy difference between donor and acceptor, the driving force and photovoltaic performance of the final device. From these studies, a chemical molecular structure-driving force- performance relationship was established, providing valuable reference for the regulation of the driving force in designing novel photovoltaic materials.