| Title: |
Rethinking Charge Transport and Recombination in Donor-diluted Organic Solar Cells |
| Authors: |
Wang, Chen; Wöpke, Christopher; Seiler, Toni; Faisst, Jared; List, Mathias; Kuhn, Meike; Joseph, Bekcy; Ehm, Alexander; Zahn, Dietrich R. T.; Vaynzof, Yana; Herzig, Eva M.; Mackenzie, Roderick C. I.; Würfel, Uli; Saladina, Maria; Deibel, Carsten |
| Publication Year: |
2026 |
| Subject Terms: |
Materials Science |
| Description: |
We systematically investigate PM6:Y12 bulk-heterojunction solar cells with donor fractions ranging from 1% to 45%, linking morphology, charge transport, and recombination to device performance. Complementary structural and spectroscopic methods reveal that a percolating PM6 network forms even at below 5% donor content, with lamellar stacking and vertical composition gradients that do not hinder the charge extraction. The reduction of the effective active layer conductivity towards low donor fractions obeys a three-dimensional percolation model, indicating that charge transport is governed by network topology rather without a pronounced percolation threshold. A transition from nongeminate Langevin recombination to a dispersive Smoluchowski-type loss occurs below 5% donor fraction. The latter regime is also nongeminate, i.e., pertains to recombination of the total charge carrier density. Correspondingly, we observe that the Langevin reduction in the higher donor fractions - mostly dominated by redissociation of electron-hole pairs after encounter - changes towards low donor fractions: in these cases, the nongeminate loss rate exceeds the prediction of the Langevin model. This regime coincides with increasing transport resistance due to topology-limited hole conduction, leading to reduced fill factors despite a high retained charge-generation efficiency. Our results demonstrate that strong donor dilution preserves photogeneration if a continuous donor network is maintained, and unveil how topology-controlled transport and non-Langevin recombination jointly define the performance limits of donor-diluted organic solar blends. |
| Document Type: |
Working Paper |
| Access URL: |
http://arxiv.org/abs/2603.08093 |
| Accession Number: |
edsarx.2603.08093 |
| Database: |
arXiv |