Relationship between exciton and charge dynamics in

organic blends through nano-morphology

Abstract: 

Exciton diffusion plays a vital role in determining the power conversion efficiency in organic semiconductor based solar cells through controlling the efficiency of exciton splitting [1]. However, measurements of diffusion length in organic semiconductors requires specialized equipment and expertise [2, 3]. Measurements of exciton splitting efficiencies rely upon quenching experiments prone to erratic errors and large uncertainties. In this presentation I will introduce a quasi-steady state technique to measure exciton diffusion lengths in organic semiconductors, named pulsed-PLQY [4]. Further, I will show how this technique can be utilized in bulk heterojunctions to measure the efficiency of exciton splitting and, also the difficult-to-measure-domain-size.[5] Finally, I will discuss the relationships between nanoscale exciton dynamics and the enhanced charge carrier dynamics seen in state-or-the-art non-fullerene organic solar cells.

The long diffusion lengths measured in non-fullerene acceptor based organic solar cells [3, 4] support large domain sizes while maintaining high exciton splitting efficiencies. These increased domain sizes can lead to large reductions in bimolecular recombination [5, 6], further impacting the efficiency of devices. Lastly, I will discuss the relationship between the enhanced charge carrier dynamics seen in state-of-the art non-fullerene organic solar cells [7] and improved exciton dynamics, enabled by the nano-morphology of the bulk heterojunction.

References:

[1] D. B. Riley, P. Meredith, A. Armin and O. J. Sandberg, "Role of Exciton Diffusion and Lifetime in Organic Solar Cells with a Low Energy Offset," The Journal of Physical Chemistry Letters, vol. 13, pp. 4402-4409., 2022. 

[2] P. Shaw, A. Ruseckas and I. Samuel, "Exciton diffusion measurements in poly (3‐hexylthiophene)," Advanced Materials, vol. 20, no. 18, pp. 3516-3520, 2008. 

[3] Y. e. a. Firdaus, "Long-range exciton diffusion in molecular non-fullerene acceptors," Nature communications, vol. 11, no. 1, pp. 1-10, 2020. 

[4] D B Riley,  et al. "Quasi-steady-state measurement of exciton diffusion lengths in organic semiconductors." Physical Review Applied 17.2 (2022): 024076. 

[5] D B Riley,  et al. "Efficient Nanoscale Exciton Transport in Non‐fullerene Organic Solar Cells Enables Reduced Bimolecular Recombination of Free Charges." Advanced Materials (2023): 2211174.

[6] M. Heiber, "Encounter-limited charge-carrier recombination in phase-separated organic semiconductor blends," Physical review letters, vol. 114, 2015. 

[7] W Li, "Organic solar cells with near-unity charge generation yield," Energy & Environmental Science, vol. 14, no. 12, pp. 6484-6493, 2021.

20231116_대학원세미나_Ardalan Armin 교수.pdf