Tailoring amphiphilic organic molecules for self assembled photovoltaic materials

有机光伏代表着一种具有成本效益的、可再生的、因此面向未来的能源供应。然而，这项技术的电力转换效率对于有机光伏的大规模使用来说仍然太低。效率低的原因可以归因于所需的施主-受主系统造成的高电压损耗以及光活性材料中的低载流子迁移率。在本项目中，正在测试一种概念，它为有机太阳能电池提供了理想的形貌。这一概念的核心在于将两亲性有机给体受体分子自组装成相分离的双层，导致具有晶体结构的给体和受体相，从而使载流子迁移率提高了数量级。此外，供体-受体界面是通过间隔分子在分子内定义的，从而使供体-受体界面在分子水平上得到优化。这种理想的形态可能会导致功率转换效率大大超过目前假设的最大15%。该项目研究和测试了通过两亲性供体-受体分子自组装成双层的可行性。首先，研究了由三个共轭亚分子(两亲性三元)组成的两亲性供体-受体分子的组成。每个分子都通过分子动力学模拟进行评估，而合适的分子则被合成并加工和表征。分子动力学模拟被用来优化两亲性分子以形成双层，大大减少了化学合成的工作量。用小角X射线散射(SAXS)、掠入射小角X射线散射(GISAXS)、掠入射广角X射线散射(GIWAXS)、扫描电子显微镜和原子力显微镜(AFM)研究了合成分子在溶液或薄膜中的形貌。这些结构信息，加上分子动力学模拟，使两亲性供体-受体分子能够连续和有效地改进。利用有机场效应晶体管(OFET)测量方法研究了薄膜中电子和空穴的输运特性，从而最终将优化的有机材料应用于太阳能电池中并进行了表征。该项目的目的是评估引入的分子概念在高效和低成本太阳能电池方面的潜力。

Organic photovoltaics represent a cost-effective, renewable and therefore future-oriented energy supply. However, the power conversion efficiencies of this technology are still too low for the large-scale use of organic photovoltaics. The reason for the low efficiency can be attributed to the high voltage losses caused by the required donor-acceptor system and the low charge carrier mobility in the photoactive material.In this project, a concept is being tested which provides an ideal morphology for organic solar cells. The core of the concept consists in the self-assembly of amphiphilic organic donor acceptor molecules into a phase-separated bilayer, leading to donor and acceptor phases with a crystalline structure which improves the charge carrier mobility by order of magnitudes. In addition, the donor-acceptor interface is defined intramolecularly via a spacer molecule, thus enabling the donor-acceptor interface to be optimized at the molecular level. This ideal morphology presumably leads to power conversion efficiencies that significantly exceed the currently assumed maximum of 15%.The project investigates and tests the feasibility of the self-assembly process by amphiphilic donor-acceptor molecules into bilayers. First, the components of the amphiphilic donor-acceptor molecule, which consists of three conjugated submolecules (amphiphilic triad), are investigated. Each molecule is evaluated by molecular dynamics simulations, whereas suitable molecules are synthesized and then processed and characterized. Molecular dynamics simulations are used to optimize the amphiphilic molecules to form bilayers, reducing significantly the effort involved in the chemical synthesis. The morphology of the synthesized molecules is investigated in solutions or in thin films using small-angle X-ray scattering (SAXS), grazing incidence small-angle X-ray scattering (GISAXS), grazing incidence wide-angle X-ray scattering (GIWAXS), scanning electron microscopy and atomic force microscopy (AFM). These structural informations, together with the molecular dynamic simulations, enable a successive and efficient improvement of the amphiphilic donor-acceptor molecule. The transport properties of electrons and holes in thin films are investigated using the organic field effect transistor (OFET) measurement method, whereby optimized organic materials are ultimately applied and characterized in solar cells. The aim of the project is to evaluate the potential of the introduced molecular concept for highly efficient and cost-effective solar cells.