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Organic semiconductors have garnered interest in wide range of applications including photovoltaics, light emission, photodetectors, sensors, and photocatalysis. Specifically, the emerging organic photovoltaics (OPVs) make use of donor-acceptor conjugated polymers in a bulk heterojunction (BHJ) morphology. Focused continued efforts in developing donor polymers and non-fullerene acceptors enabled the power conversion efficiency (PCEs) of single-junction solar cells over 19% today.[1,2] With the aim of further improving PCEs and stability of OPVs, efforts have been expended on understanding structure-processing-stability-property interrelations, which necessitates molecular-level understanding of thin film morphology of the photoactive layer, contact layers and interfaces between them. Here we provide a method to resolve structure-property relationships in OPVs using multiscale characterization and device physics including charge generation, extraction and recombination processes.[3] Synergism between the X-ray diffraction, solid-state NMR/EPR and modelling techniques enabled the bulk and interfacial morphology in BHJ thin films and contact layers to be resolved and distinguished.[3,4] We will discuss the state-of-the-art 2D NMR and EPR spectroscopy and imaging techniques suitable for resolving thin film morphology in PM6:Y6 solar cells at atomic-scale resolution. In addition, we will demonstrate how a hybrid bottom-up and top-down NMR crystallography approach in conjunction with device physics can be used to establish structure-property relationships in NFA based OPVs.[4,5] Our approach can be further extended to resolve structure-stability-property relationships in high performance organic photodetectors (OPDs) and organic electrochemical transistors (OECTs).
References:
1. L. Zhu, M. Zhang, J. Xu, C. Li, J. Yan, G. Zhou, W. Zhong, T. Hao, J. Song, X. Xue, Z. Zhou, R. Zeng, H. Zhu, C.-C. Chen, R.C. I. MacKenzie, Y. Zou, J. Nelson, Y. Zhang, Y. Sun, F. Liu, Single-junction organic solar cells with over 19% efficiency enabled by a refined double-fibril network morphology. Nature Materials 2022, 21 (6), 656-66.
2. Y. Cui, Y. Xu, H. Yao, P. Bi, L. Hong, J. Zhang, Y. Zu, T. Zhang, J. Qin, J. Ren, Z. Chen, C. He, X. Hao, Z. Wei, J. Hou, Single-Junction Organic Photovoltaic Cell with 19% Efficiency. Adv. Mater. 2021, 33, 2102420.
3. B. R. Luginbuhl, P. Raval, T. Pawlak, Z. Du, T. Wang, G. Kupgan, N. Schopp, S. Chae, S. Yoon, A. Yi, H. J. Kim, V. Coropceanu, J.-L. Brédas, T.-Q. Nguyen, G. N. M. Reddy, Resolving Atomic-Scale Interactions in Nonfullerene Acceptor Organic Solar Cells with Solid-State NMR Spectroscopy, Crystallographic Modelling, and Molecular Dynamics Simulations. Adv. Mater. 2022, 34, 2105943.
4. A. Karki, J. Vollbrecht, A. J. Gillett, S. S. Xiao, Y. Yang, Z. Peng, N. Schopp, A. L. Dixon, S. Yoon, M. Schrock, H. Ade, G. N. M. Reddy, R. H. Friend, T.-Q. Nguyen, The role of bulk and interfacial morphology in charge generation, recombination, and extraction in non-fullerene acceptor organic solar cells, Energy Environ. Sci. 2020, 13, 3679.
5. A. L. Dixon, H. Vezin, T.-Q Nguyen, G. N. M. Reddy, Structural insights into Lewis acid and F4TCNQ doped conjugated polymers by solid-state magnetic resonance spectroscopy. Materials Horizons, 2022, 9, 981-990.
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