Interfacial energetics and charge carrier dynamics in organic and hybrid photo electron sensors

有机和混合光电传感器中的界面能量学和载流子动力学

• 批准号: 2122936
• 金额: --
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2122936
• 关键词: Interfacial; energetics; charge; carrier; dynamics

Harvesting solar light by conversion of photons into electric charges is one of the most promising strategy to tackle energetic crisis and global warming providing a clean source of power. At the same time organic semiconductors can also act as wavelength-selective radiation sensors when operated in reverse bias. While traditional solar cells and photodetectors are still relying on silicon and to the well understood mechanisms of charge transport in the ordered molecular structure of inorganic crystals, in the last decades substantial progresses have been achieved for a profitable manufacture of organic semiconductors. These materials offer a wide range of advantages such as the possibility of solution-based and cheap processing, transparency and light weight together with flexibility and biocompatibility for integrable and wearable devices.Energy production in organic solar cells (OSCs) and organic photodetectors (OPDs) is based on the light-excitation of molecules and hopping of the formed localised excitons along the pi-conjugated structure. Moreover, the most common active layer for OSCs nowadays is comprised of an interpenetrating blend of a donor (D) and an acceptor (A) material, the so-called Bulk Heterojunction, where the continuous D:A interface provides the energy offset for exciton separation and charge extraction. All these processes are still not thoroughly understood and they present numerous scientific issues due to the loss mechanisms such as geminate and bimolecular recombination.Because of these phenomena specific to organic materials, OSCs lag behind silicon cells in terms of Power Conversion Efficiency (PCE) and OPD performances are still difficult to control as for detectivity and dark current. However, these devices can offer a reliable and economically profitable technology if they can guarantee an extended period of operativity. Therefore, one of the key challenges in the field is to identify and control the efficiency loss mechanisms in order to improve their stability in various operational conditions.This project aims to tackle this stability issue by identifying the loss mechanisms. We will focus on a specific class of molecules applied in photovoltaics and photodetectors, which will include new Non-Fullerene Acceptors (NFAs) and novel small molecule donor materials.Since these families of materials offer a rich toolbox of molecular design strategies to tailor their properties, an important aim of this study is to investigate optoelectronic properties and thin film morphology of different molecules by techniques like Raman spectroscopy for vibrational mode analysis, Photoemission Spectroscopy for investigation of energetics and Atomic Force Microscopy to visualise surface topography.Alongside the characterisation of neat materials and respective blends, device fabrication represents an essential part of the work, allowing to assess how properties of different species have outcomes on device efficiency.The core objective of the project is the understanding of light-induced degradation mechanisms in thin films and operational devices in order to identify ways to improve the OSC lifetime and OPD robustness. By doing so, we aim at identifying the best molecular engineering routes for the fabrication of highly stable devices - e.g. highlighting which structural properties of molecules are critical and beneficial to avoid loss mechanisms of radiative and non-radiative recombination.With regards to OSCs, the realisation of devices with novel NFAs and suitable donors providing both good PCE and long operational stability under illumination and thermal conditions comparable to the real working environment would be a satisfactory result to demonstrate how organic-based electronics can be a reliable technology for forthcoming commercialisation on the market.

通过将光子转化为电荷来收集太阳能是解决能源危机和全球变暖最有希望的策略之一，它提供了一种清洁的能源。同时，在反向偏置下，有机半导体也可以作为波长选择辐射传感器。虽然传统的太阳能电池和光电探测器仍然依赖于硅和无机晶体有序分子结构中电荷传输的良好理解机制，但在过去的几十年里，有机半导体的盈利制造取得了实质性进展。这些材料提供了广泛的优势，例如基于解决方案和廉价加工的可能性，透明度和重量轻，以及可集成和可穿戴设备的灵活性和生物相容性。有机太阳能电池（OSCs）和有机光电探测器（OPDs）的能量产生是基于分子的光激发和沿π共轭结构形成的局域激子的跳跃。此外，目前最常见的OSCs活性层由供体(D)和受体(a)材料的互穿混合物组成，即所谓的体异质结，其中连续的D: a界面为激子分离和电荷提取提供了能量偏移。所有这些过程仍然没有被完全理解，并且由于诸如双分子重组和双分子重组等损失机制，它们提出了许多科学问题。由于有机材料特有的这些现象，OSCs在功率转换效率（PCE）方面落后于硅电池，OPD性能在探测性和暗电流方面仍然难以控制。然而，如果这些设备能够保证较长时间的运行，则可以提供可靠且经济上有利可图的技术。因此，该领域的关键挑战之一是识别和控制效率损失机制，以提高其在各种操作条件下的稳定性。本项目旨在通过确定损失机制来解决这一稳定性问题。我们将专注于光伏和光电探测器中应用的一类特定分子，其中包括新的非富勒烯受体（nfa）和新的小分子供体材料。由于这些材料家族提供了丰富的分子设计策略工具箱来定制其特性，因此本研究的一个重要目的是通过拉曼光谱（用于振动模式分析）、光电光谱（用于研究能量学）和原子力显微镜（用于可视化表面形貌）等技术来研究不同分子的光电特性和薄膜形态。除了整齐材料和各自混合物的特征外，设备制造代表了工作的重要组成部分，允许评估不同物种的特性如何对设备效率产生影响。该项目的核心目标是了解薄膜和操作设备中的光致降解机制，以确定改善OSC寿命和OPD鲁棒性的方法。通过这样做，我们的目标是确定制造高度稳定器件的最佳分子工程路线-例如，突出分子的哪些结构特性是关键的，有利于避免辐射和非辐射重组的损失机制。在OSCs方面，实现具有新型nfa和合适供体的设备，在与实际工作环境相当的照明和热条件下提供良好的PCE和长时间的操作稳定性，将是一个令人满意的结果，证明有机电子技术如何成为即将在市场上商业化的可靠技术。