arXiv subjects

Toni Seiler

Publications and source records attributed to Toni Seiler.

5 recordsLinked to original sources

arXiv2026

Rethinking Charge Transport and Recombination in Donor-diluted Organic Solar Cells

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.

cond-mat.mtrl-sci↗

arXiv2026

Bridging the lab-to-fab gap in non-fullerene organic solar cells via gravure printing

Organic solar cells have reached record efficiencies with non-fullerene acceptors, yet their translation to industrial printing remains a critical bottleneck. Here we report the highest efficiency achieved for a fully roll-to-roll-compatible gravure-printed non-fullerene organic solar cell. High-performance blends are typically optimised under laboratory coating conditions, while roll-to-roll manufacturing imposes fundamentally different constraints on ink stability, drying dynamics, and multilayer integration. Whether these constraints intrinsically limit device physics has remained unresolved. Here, we demonstrate a gravure-printed PM6:Y12 solar cell architecture using commercially available materials and establish a quantitative framework that disentangles optical, recombination, and transport losses in printed devices. We find that favourable bulk morphology and exciton harvesting can be preserved under gravure printing and non-halogenated solvents. The dominant efficiency penalties arise instead from optical interference within the printed layer stack and slow charge transport. Our results demonstrate that the performance gap between laboratory and printed solar cells is originating from device architecture rather than the intrinsic physics of modern non-fullerene systems, providing a mechanistic roadmap for roll-to-roll manufacturing of non-fullerene solar cells.

cond-mat.mtrl-sci↗

arXiv2025

The contribution of electron and hole conductivity to the transport loss in organic solar cells

The effective conductivity determines the reciprocal of the transport resistance, the dominant loss of fill factor in organic solar cells. We experimentally determine the dependence of effective conductivity on its electron and hole contributions. Using PM6:Y12 blends with tunable morphological and energetic disorder, we show that the effective conductivity follows a harmonic mean of electron and hole conductivities even across nearly three orders of magnitude in conductivity imbalance. We also validate the method for directly extracting effective conductivity from current-voltage measurements, eliminating the need to rely on indirect mobility and charge carrier density-based proxies. Our findings challenge the widespread use of geometric mean approximations and offer a more accurate framework for analysing and modelling transport in disordered organic semiconductors.

cond-mat.mtrl-sci↗

arXiv2024

Barkhausen noise in the columnar hexagonal organic ferroelectric BTA

Upon a polarization reversal within a ferroelectric material, one stable state changes into another which is typically described by a progression of switching events of smaller fractions of the material. These events give rise to crackling or Barkhausen noise and follow a characteristic distribution in their sizes. Barkhausen noise has been studied to better understand the switching processes of ferroelectrics and has been applied for inorganic ferroelectric materials and perovskites. In this work, we present results from kinetic Monte Carlo simulations investigating the switching process of the small organic molecular ferroelectric benzene-1,3,5-tricarboxamides (BTAs). For temperatures below 175 K and sufficiently strong structural disorder, the system exhibits self-organized critical behavior; for higher temperatures, a creep regime is entered. Our extracted power-law exponents are smaller than those typically measured in inorganic crystals and ceramics which indicates that in the more disordered material BTA larger spanning avalanches are possible. The system was experimentally investigated with a high-sensitivity setup. No Barkhausen noise was observed which is consistent with the simulated event sizes, lying several orders beneath the noise threshold of the experimental setup. This finding corroborates the notion that switching in BTA progresses along the 1D columns in the hexagonal liquid crystal lattice, with little coupling between the columns that could give rise to larger lateral avalanches.

cond-mat.mtrl-sci↗

arXiv2024

Barkhausen noise in the organic ferroelectric copolymer P(VDF:TrFE)

Polarization reversal within a ferroelectric material is commonly described as a progression of smaller switching events, giving rise to crackling or Barkhausen noise. While studies on Barkhausen noise, and particularly the associated event size distribution, allow for better understanding of switching processes in ferroelectrics, they were not yet conducted experimentally on organic ferroelectric materials. In this work, Barkhausen noise in the organic ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF:TrFE)) is experimentally investigated under different electric fields, increasing at various rates. A weak dependence of the structure of the Barkhausen noise on both the magnitude and rise time of the applied electric field is observed, which manifests as a trend in the probability density function power-law exponents. Specifically, an increase in maximum electric field leads to an increase of the power-law exponent; increasing the rise time causes a parallel shift towards lower exponents. While these findings do not allow to conclusively confirm or refute universal self-organized critical behavior of the polarization reversal avalanches in P(VDF:TrFE), the exponents were found to seemingly converge to the universal value of 1.5 for fast and strong driving, suggesting the system is close to this limit.

cond-mat.mtrl-sci↗