Investigation of materials and devices for organic photovoltaics by EPR and EDMR

本研究项目将通过EPR（电子顺磁共振）和EDMR（电检测磁共振）光谱研究有机光伏系统材料和器件的基本过程。它主要属于物理科学主题中的EPSRC分析科学和能源应用材料研究领域的福尔斯，并对能源主题有实际应用。有机光伏系统涉及供体和受体分子的混合物，在光激发后，形成单重态激子，然后通过供体-受体界面的电荷转移解离成自旋相关的自由基对。这种自由基对的特征在于可以通过EPR光谱检测到的耦合未成对电子自旋。在过去，EPR和EDMR光谱已被用于研究硅太阳能电池和富勒烯基有机太阳能电池中的一系列不同的自旋中心。目前，有机光致发光材料的研究主要集中在非富勒烯受体上，这些受体可以提高能量转换效率。基于非富勒烯受体的光伏电池在过去十年中已经显示出效率的巨大增长，其速度比类似的基于富勒烯的受体快得多。由于EPR和EDMR可以跟踪从电荷转移状态到分离电荷的演变，因此该项目的目的是使用这些方法来更好地了解包括最先进的非富勒烯受体的供体-受体共混物的这一过程。不同的连续波和脉冲EPR和EDMR实验将被用来阐明有机光致发光材料中自旋中心的性质和动力学。特别是，自旋中心与其分子环境的相互作用，包括超精细的相互作用，附近的磁核和偶极和交换自旋中心之间的相互作用，将使用先进的脉冲EPR和EDMR技术进行研究。其目的是获得分子水平的洞察力的电荷分离，重组和运输过程相关的太阳能电池的操作，并确定有效的能量转换的分子要求。数字电子学的最新发展使得整形脉冲能够集成到脉冲EPR序列中。与传统的矩形脉冲相比，成形脉冲允许增加自旋控制和设计具有增加的灵敏度和在磁相互作用的表征中具有增加的准确性的新实验。整形脉冲已被证明可以提高EPR生物系统结构表征的灵敏度，但迄今为止还没有被用于帮助研究有机电子材料中的自旋中心。该项目将涉及开发EPR实验，以利用成形脉冲在这些材料中的自旋特性方面的优势。在EDMR中，整形脉冲的使用目前在很大程度上仍未得到开发，因此，该项目还将旨在通过纳入整形脉冲和设计新型脉冲序列来进一步开发脉冲EDMR方法，这些脉冲序列利用它们提供的增强的自旋控制。这个项目，在物理，化学和材料科学的接口，是与EPSRC的跨学科研究的重点对齐。从EPR和EDMR光谱学中获得的关于有机光化学中太阳能转化为电能的基本过程的见解将对太阳能技术领域具有重要意义。所开发的方法和途径还与物理科学主题中的许多其他研究领域相关，包括光电子学，自旋电子学和量子计算。

This research project will study fundamental processes in materials and devices for organic photovoltaic systems through investigation by EPR (Electron Paramagnetic Resonance) and EDMR (Electrically Detected Magnetic Resonance) spectroscopy. It primarily falls within the EPSRC Analytical Science and Materials for Energy Applications research areas within the Physical Sciences theme and has practical applications to the Energy theme as well.Organic photovoltaic systems involve a blend of donor and acceptor molecules that, after excitation by light, form singlet excitons that can then dissociate into a spin-correlated radical pair by charge transfer at a donor-acceptor interface. This radical pair is characterised by coupled unpaired electron spins that can be detected by EPR spectroscopy. Efficient charge separation over recombination of the radical pair is critical for an effective organic photovoltaic system.In the past, EPR and EDMR spectroscopy have been used to investigate a range of different spin centres in silicon solar cells and in fullerene-based organic solar cells. Currently, research in organic photovoltaics is focused on non-fullerene acceptors that have led to increased energy conversion efficiencies. Photovoltaic cells based on non-fullerene acceptors have been showing tremendous growth in efficiency in the last decade at a much faster rate than similar fullerene-based acceptors. Since EPR and EDMR can follow the evolution from a charge-transfer state to separated charges, the aim of the project is to use these methods to gain a better insight into this process for donor- acceptor blends including state-of-the-art non-fullerene acceptors. Different continuous-wave and pulse EPR and EDMR experiments will be used to characterise the nature and dynamics of the spin centres in materials for organic photovoltaics. In particular, the interactions of the spin centres with their molecular environment, including hyperfine interactions to nearby magnetic nuclei and dipolar and exchange interactions between spin centres, will be investigated using advanced pulse EPR and EDMR techniques. The aim is to gain molecular-level insight into the charge separation, recombination, and transport processes relevant for solar cell operation and to identify molecular requirements for efficient energy conversion. Recent developments in digital electronics have enabled the integration of shaped pulses into pulse EPR sequences. Compared to traditional rectangular pulses, shaped pulses allow increased spin control and the design of new experiments with increased sensitivity and with increased accuracy in the characterisation of magnetic interactions. Shaped pulses have been demonstrated to achieve increased sensitivity for structural characterisation of biological systems by EPR but have so far not been used to aid the investigation of spin centres in materials for organic electronics. This project will involve development of EPR experiments tailored to exploit the advantages of shaped pulses in the characterisation of spins in these materials. Within EDMR, the use of shaped pulses is currently still largely unexplored, therefore, this project will also aim to develop the pulse EDMR method further through the inclusion of shaped pulses and the design of novel pulse sequences that leverage the increased spin control they provide. This project, at the interface of physics, chemistry, and materials science, is aligned with the EPSRC's focus on interdisciplinarity in research. The insights gained from EPR and EDMR spectroscopy on the fundamental processes involved in the conversion of solar energy to electricity in organic photovoltaics will have great significance for the field of solar energy technology. The developed methods and approaches are additionally relevant to many other research areas within the Physical Sciences theme, including optoelectronics, spintronics and quantum computing.