高介电常数含硫侧链共轭聚合物制备及其在聚合物光伏器件中的应用与机制研究

Since the discovery of ultra-fast photo-induced charge transfer from conjugated polymers (CPs) to fullerene, the organic/polymeric photovoltaic solar cells (OPVs) have attracted much attention. Tremendous efforts have been employed, and the recorded power conversion efficiencies (PCEs) of the OPVs are boosted up to 17.3% that are still much lower inorganic solar cells. In recently, many theoretical proofs have revealed that the much lower PCEs for the OPVs are mainly attributable to the fundamental characteristics like of higher exciton banding energy, charge-carrier recombination and lower relative dielectric constants etc. of OPVs materials medium in contrast to those for their inorganic counterparts. The dielectric constant is believed an overwhelming important parameter, and enhancing the dielectric constants would resulted in reducing the exciton banding energy, charger-transfer recombination, space-charge effects and enhancement of the exciton dissociation etc. of the OPVs, thus potentially bridge the gap between present OPVs and their rival inorganic counterparts. Even so, only a limited number of studies, in which the functionalities like of (oligo)ethylene glycol, -CN substituted alkyl and fluorine atoms etc. were employed to achieve high dielectric constants OPVs materials, have been presented so far. However, the employment of (oligo)ethylene glycol, fluorine atoms or cyano group can result in the simultaneous improvement of the dielectric properties and the open circuit voltage of the corresponding OPVs, alongside with the employment of the expensive and toxic agents, narrowing the light photo response in some case. .As compared with the oxygen atoms, the sulphur atoms not only exhibit weaker electron-donating ability in relative to that of oxygen atom and some π-acceptor capability due to the formation of pπ(C)-dπ(S) orbital overlap, but also present higher mole refractive index due to the easily polarized two electrons pairs and outer d-orbit of sulphur atom. In these lines, aforementioned characteristics of sulphur atom might cause the CPs containing alkylthio side chains not only exhibiting unique optoelectronic properties, but also presenting enhanced mole refractive index, and thus potentially providing higher dielectric constants as compared with those for the CPs containing alkoxy or alkyl side chains. To date, many promising CPs donors containing alkylthio side chains have been presented, and the advantages like of deepening the HOMO energy levels, increasing the extinction co-efficiencies and charge transporting characteristics decreasing the exciton dissociation probabilities etc. of CPs with alkylthio side chains as compared with their counterparts CPs with alkyl or alkyloxy side chains, have been verified. However, the influence of alkylthio side chains on the dielectric constants of the CPs were never been followed up so far..In order to solve out the limit of further performance-enhancing of OPVs because of low dielectric constants of CPs, in this project, the strategy of designing and synthesizing high dielectric constants CPs/non-fullerene electron acceptor materials, combined by device engineering (device structure, device fabrication process etc.) optimization is developed. Therefore, firstly a series of more than 40 kinds of high dielectric constants donor CPs by introducing many sulfur atoms into electron-rich thienoacene-based derivatives and other photovoltaic units are synthesized. Then, they are prepared that are a family of high dielectric constants non-fullerene electron acceptors by incorporating polysulfide pendant group. Finally, the relevant device engineering parameters and dynamics mechanism are recognized via optimizing the dielectric constant of polymers and device engineering parameters, which will support new basis and opportunity for designing and developing new efficient OPVs materials, as well as deepening and developing organic/polymer semiconductor physics theory.

申请项目以设计合成高介电常数给体聚合物/非富勒烯受体光伏材料为主要策略，结合器件工程学（器件结构、器件制备工艺）优化，以期解决由于现有主要光伏材料过低的介电常数，限制有机/聚合物光伏（OPVs）性能突破到新的水平的关键科学问题。因此，首先通过将含多个硫原子的多硫醚侧基引入到噻并苯衍生物富电子单元或OPVs电子给体聚合物中常用的缺电子体单元中，构建一系列约40余种高介电常数的共轭聚合物电子给体材料。其次，将含多个硫原子的烷基多硫醚侧基引入非富勒烯受体中，合成得到高介电常数的非富勒烯电子受体材料。随后，利用新合成的高介电常数电子给体和受体材料结合器件工程学优化，以期实现OPVs 器件能量转换效率的突破。最后，通过聚合物介电常数及器件工程学优化参数，认识相关器件工程学参数和动力学机制，为设计、开发新的高效OPVs 材料、以及深化和发展有机/聚合物半导体物理理论提供新的支撑和契机。

本项目以“基于烷硫基噻吩基侧基取代噻并苯衍生物高介电常数共轭聚合物合成与表征及器件载流子动力学机制研究”为基础，合成了一系列高介电常数的光伏材料（介电常数≥6）。通过在噻并苯侧基引入多硫原子来提高光伏材料的相对介电常数，发现聚合物介电常数的提高能够有效抑制双分子的复合，进而提高短路电流密度（JSC）和填充因子（FF），实现有机/聚合物光伏（OPVs）器件的能量转换效率（PCEs）的突破。通过聚合物介电常数及器件工程学优化参数对相应OPVs器件性能的影响，以及器件界面能级、电荷转移能态、瞬态光电压/光电流特性等系统研究，认识相关器件工程学参数、活性层介电常数对其载流子的产生、分离、复合、传输动力学影响机制，为设计、开发新的高效OPVs材料、以及深化和发展有机/聚合物半导体物理理论提供新的支撑和契机。本项目中创造性地将多硫醚侧基引入到共轭聚合物侧链，合成高介电常数的OPVs给体材料，提出并证明是一种解决因现有主要光伏材料过低的介电常数，限制OPVs性能的突破到新水平的新策略。