Research Seminars in Physics

Monday, 19 February 2024, 13:30
Where: 21D302 

Speaker: Suraj Prasad, Department of Engineering and Physics, Karlstad University

Title: Effect of molecular structure on the photochemical stability of small molecule and polymer acceptors used in organic solar cells

Abstract:

Organic photovoltaics (OPV) represent an affordable solar energy solution utilizing thin layers of molecular semiconductor materials, offering distinct benefits such as lightweight construction, flexibility, and ease of large-scale production when compared to conventional PV technologies. Recently, there has been a surge of interest in OPV due to notable advancements in power conversion efficiency, reaching up to 19%, notably with the use of innovative small-molecule non-fullerene acceptors (NFAs).[1,2] However, the limited operational lifespan of organic solar cells remains a significant hurdle in their commercial viability, primarily attributed to the inherent photostability challenges of the conjugated molecules forming the photoactive layer. In my doctoral research, we focused on investigating the photostability of a selection of cutting-edge donor and acceptor materials, including PBDB-T, Y5, PF5-Y5, and PYT thin films, under simulated sunlight (AM1.5) in ambient conditions. We monitored their characteristics over time using various spectroscopic methods such as UV-Vis absorption, Fourier-Transform Infrared (FTIR), as well as X-Ray and Ultraviolet Photoelectron Spectroscopy (XPS and UPS). Our findings revealed that the absorption spectra of Y5 and PYT films remained largely unaffected even after 30 hours of light exposure, while the PF5-Y5 and PBDB-T films experienced rapid photobleaching. Notably, the substitution of the BDT-T unit with thiophene in PYT significantly enhanced its stability, underscoring the substantial influence of the co-monomer nature on the intrinsic photostability of Y5-based copolymers. These insights are anticipated to inspire the development of stable donor and acceptor polymers crucial for the realization of long-lasting OPV devices. In the next phase of my PhD project, I aim to delve into the photo-physics of devices upon photodegradation.

References

1. L. Zhu, M. Zhang, J. Xu, C. Li, J. Yan, G. Zhou, W. Zhong, T. Hao, J. Song & X. Xue. Single-junction organic solar cells with over 19% efficiency enabled by a refined double-fibril network morphology. Nature Materials 21, 656-663 (2022).

2. H. Meng, W. Jing, X. Xu, L. Yu & Q. Peng. Nickel (II) Nitrate Hole‐Transporting Layers for Single‐Junction Bulk Heterojunction Organic Solar Cells with a Record 19.02% Efficiency. Angewandte Chemie 135, e202301958 (2023).

https://www.kau.se/en/physics/research/research-seminars-physics