Separating microstructure-related from photo-induced degradation mechanisms in NFA based organic solar cells (Project 9)

从富勒烯基到非富勒烯基受体（NFA）的转变消除了有机太阳能电池（OSC）中的两个主要降解过程：富勒烯二聚化和富勒烯扩散。第一次实验证明了所选NFA复合材料的前所未有的器件寿命。P3 HT：我们的团队最近连续运行IDTBR太阳能电池超过25000小时，在1太阳等效LED照明和低于40摄氏度的温度下没有明显的退化迹象。然而，已知较高的温度以及UV /蓝光在OSC中诱导不同的降解机制。我们最近的研究首次揭示了这些降解过程背后的机制。我们发现了一个明确表达的光降解的波长依赖性，达到远到500 nm的制度。此外，我们发现控制电荷产生界面的维度和密度是增强热稳定性的关键参数。控制供体/ NFA微结构对P9-Brabec/Li至关重要。体异质结（BHJ）复合材料，双层（BL）以及伪双层（PBL）太阳能电池将通过传统的印刷技术，通过层转移或通过正交溶剂处理。这种方法的目的是控制有源层的微观结构，使我们能够从一个纯粹的双层，通过一个相互扩散的双层器件，并最终以一种受控的方式优化体异质结调整的设备。热降解以及光谱分辨光致降解将分别研究这些参考架构，并与经典的本体异质结的概念。部分完成的太阳能电池堆的退化将允许研究相邻层之间的相互作用，并有助于确定主要的退化机制。机器学习技术将把来自各种表征技术（如吸收、瞬态PL和电学测量）的数据关联起来，为有机光伏（OPV）稳定性研究提供预测框架。基于在该项目中获得的知识，将采用几种策略来减轻热和光化学降解，并制造高度稳定的实验室规模的设备。

Transition from fullerene based to non-fullerene-based acceptors (NFAs) has eliminated two major degradation processes in organic solar cells (OSCs): fullerene dimerization and fullerene diffusion. First experiments evidenced unprecedented device lifetime for selected NFA composites. P3HT:IDTBR solar cells were recently operated by our groups for over 25000 hrs continuously without obvious signs of degradation under 1 sun equivalent LED illumination and at temperatures below 40◦C. However, higher temperatures as well as UV / blue light are known to induce distinct degradation mechanisms in OSCs. Our recent investigations provided first in-sight into the mechanisms behind these degradation processes. We found a distinctly expressed wavelength dependence for photodegradation, which reached far into the 500 nm regime. More-over, we found that controlling the dimensionality and density of charge generating interfaces is a key parameter to enhanced thermal stability. Controlling the donor / NFA microstructure is of central importance to P9–Brabec/Li. Bulk heterojunction (BHJ) composites, bilayer (BL) as well as pseudo bilayer (PBL) solar cells will be made by conventional printing techniques, by layer transfer or by orthogonal solvent processing. This approach aims to control the active layer microstructure, giving us the ability to tune the device from a pure bilayer, through to an inter-diffused bilayer device and finally to an optimised bulk heterojunction in a controlled way. Thermal degradation as well as spectrally resolved photo induced degradation will be separately studied for these reference architectures and compared to the classical bulk heterojunction concept. Degradation of partially finished solar cell stacks will allow to investigate interactions between neighbouring layers and help identify the leading degradation mechanisms. Machine Learning Techniques will correlate the data from various characterization techniques as absorption, transient PL and electrical measurements to provide a predictive framework for organic photovoltaic (OPV) stability investigations. Based on the knowledge gained in this project, several strategies will be employed to mitigate thermal as well as photo-chemical degradation and to fabricate highly stable lab scale devices.