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@article{nokey,

title = {Highly Crystalline and Oriented Thin Films of Fully Conjugated 3D-Covalent Organic Frameworks},

author = {I Munoz-Alonso and D Bessinger and S Reuter and M Righetto and L Fuchs and M D\"{o}blinger and D D Medina and F Ortmann and L M Herz and T Bein},

url = {\<Go to ISI\>://WOS:001525541100001},

doi = {10.1002/anie.202505799},

year  = {2025},

date = {2025-06-15},

journal = {Angewandte Chemie-International Edition},

abstract = {Fully conjugated 3D covalent organic frameworks (COFs) are a newly emerged class of materials that expands reticular chemistry to extended electron delocalization for optoelectronic applications. To overcome the limitations of sp3-connected 3D frameworks, the pseudo-tetrahedral motif cyclooctatetrathiophene (COTh) has gained attention for forming fully conjugated 3D COFs. We report on a novel COTh building block, featuring functional formyl groups directly attached to the core's conjugated thiophenes. The modulation synthesis approach with mono-functionalized inhibitors enables the formation of COTh-1P COF, which exhibited remarkable crystallinity and permanent porosity. By following this approach and by optimizing the synthesis conditions for the solvothermal growth of thin films, we fabricated the first preferentially oriented conjugated 3D COF films on various substrates without pre-functionalization. With these thin films, optical pump terahertz probe studies allowed us, for the first time with 3D-fully conjugated COFs, to provide insights into the excited state and charge-carrier dynamics of these unique organic frameworks. Low effective masses are discovered for valence and conduction bands by density functional theory simulations. The ability to create crystalline and oriented films of fully pi-conjugated 3D COTh-based COFs on non-modified substrates is expected to open the way for integration of such frameworks into diverse optoelectronic applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Insights into Decoupled Solar Energy Conversion and Charge Storage in a 2D Covalent Organic Framework for Solar Battery Function},

author = {B B Rath and L Fuchs and F Stemmler and A Rodr\'{i}guez-Camargo and Y Wang and M F X Dorfner and J Olbrich and J Van Slageren and F Ortmann and B V Lotsch},

url = {https://doi.org/10.1021/jacs.4c17642},

doi = {10.1021/jacs.4c17642},

issn = {0002-7863},

year  = {2025},

date = {2025-04-28},

journal = {Journal of the American Chemical Society},

abstract = {Decoupling solar energy conversion and storage in a single material offers a great advantage for off-grid applications. Herein, we disclose a two-dimensional naphthalenediimide (NDI)-based covalent organic framework (COF) exhibiting remarkable solar battery performance when used as a photoanode. Light-induced radicals are stabilized within the framework for several hours, offering on-demand charge extraction for electrical energy production. Our study reveals mechanistic insights into the long-term charge stabilization using optical spectroscopy and (photo)electrochemical measurements, in conjunction with density functional theory (DFT) simulations. Among several solvents, water provides the best dielectric screening and energetically favorable proton exchange to stabilize photoinduced radicals for more than 48 h without the need for additional metal cations. This study provides fundamental insights into the optoionic charge storage mechanism in NDI-COF, while introducing a highly tunable, nanoporous material platform that surpasses related materials, such as carbon nitrides, metal\textendashorganic frameworks (MOFs), or metal oxides, in terms of charge storage capacity. This study opens new perspectives for the design of optoionic charge-storing materials and the direct storage of solar energy to overcome the intermittency of solar irradiation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Effective Electron-Vibration Coupling by Ab Initio Methods},

author = {M F X Dorfner and F Ortmann},

url = {https://doi.org/10.1021/acs.jctc.4c01608},

doi = {10.1021/acs.jctc.4c01608},

issn = {1549-9618},

year  = {2025},

date = {2025-03-11},

journal = {Journal of Chemical Theory and Computation},

volume = {21},

number = {5},

pages = {2371-2385},

abstract = {The description of electron\textendashphonon coupling in materials is complex, with varying definitions of coupling constants in the literature and different theoretical approaches available. This article analyzes different levels of theory to introduce and compute these coupling constants. Within the quasi-particle picture, we derive an effective linear-coupling Hamiltonian, describing the interaction of electronic quasi-particles with vibrations. This description allows a comparison between coupling constants computed using density functional theory and higher-level quasi-particle approaches by identifying the Kohn\textendashSham potential as an approximation to the frequency-independent part of the self-energy. We also investigate their dependence on the exchange-correlation (XC) functional. Despite significant deviations of the Kohn\textendashSham eigenvalues, which arise from different XC functionals, the resulting coupling constants are remarkably similar. A comparison to quasi-particle methods, such as the well-established G0W0 approach, reveals significant quasi-particle weight renormalization. Surprisingly, however, in nearly all the considered cases, the coupling constants computed in the DFT framework are excellent approximates of the ones in the quasi-particle framework, which is traced back to a significant cancellation of competing terms. Other quasi-particle methods, such as the Outer Valence Green’s Function approach and the ΔSCF method, are also included in the comparison. Moreover, we investigate the coupling of vibrations to excitonic excitations and find, by comparison to time-dependent density functional theory and extended multiconfiguration quasi-degenerate second-order perturbation theory, that knowing the underlying electron- and hole-vibration couplings is sufficient to accurately determine the exciton-vibration coupling constants in the studied cases.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Predicting 2D Crystal Packing in Thin Films of Small Molecule Organic Materials},

author = {A O Gudovannyy and J M Sch\"{a}fer and O Gerdes and D Hildebrandt and G Mattersteig and M Pfeiffer and F Ortmann},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202421048},

doi = {https://doi.org/10.1002/adfm.202421048},

issn = {1616-301X},

year  = {2025},

date = {2025-01-07},

journal = {Advanced Functional Materials},

volume = {n/a},

number = {n/a},

pages = {2421048},

abstract = {Abstract The large variety of structural morphologies realized in organic semiconductors is a big challenge for the microscopic modeling of such systems. A global computational solution is still out of reach due to prevalent molecular flexibility. However, the specific case of crystalline thin films that exhibit surface alignment of molecular π-systems for optoelectronic applications of high technological relevance, seems to be a simpler task. This study proposes an approach for the structure prediction of two-dimensional (2D) molecular layers as precursors for the three-dimensional (3D) structure of deposited crystalline thin films. Based on grid search sampling for the layer's degrees of freedom, it requires only a small number of trial structures to find complex packing motifs of layered molecular materials. It facilitates parallel screening among multiple molecular conformers, which is usually very difficult and expensive, using the latest 3D-based prediction methods. The study researches theoretically and experimentally a set of known and newly crystallized compounds of evaporable flexible molecules with interesting optoelectronic properties, predicts their packing in 2D layers, and compares them with experimentally resolved crystal structures, obtaining very good agreement in the packing of these molecules within layers. The computational costs are estimated to be several orders of magnitude lower than with 3D methods.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Spatiotemporal Spectroscopy of Fast Excited-State Diffusion in 2D Covalent Organic Framework Thin Films},

author = {L Spies and A Biewald and L Fuchs and K Merkel and M Righetto and Z Xu and R Guntermann and R Hooijer and L M Herz and F Ortmann and J Schneider and T Bein and A Hartschuh},

url = {https://doi.org/10.1021/jacs.4c13129},

doi = {10.1021/jacs.4c13129},

issn = {0002-7863},

year  = {2025},

date = {2025-01-02},

journal = {Journal of the American Chemical Society},

abstract = {Covalent organic frameworks (COFs), crystalline and porous conjugated structures, are of great interest for sustainable energy applications. Organic building blocks in COFs with suitable electronic properties can feature strong optical absorption, whereas the extended crystalline network can establish a band structure enabling long-range coherent transport. This peculiar combination of both molecular and solid-state materials properties makes COFs an interesting platform to study and ultimately utilize photoexcited charge carrier diffusion. Herein, we investigated the charge carrier diffusion in a two-dimensional COF thin film generated through condensation of the building blocks benzodithiophene-dialdehyde (BDT) and N,N,N′,N′-tetra(4-aminophenyl)benzene-1,4-diamine (W). We visualized the spatiotemporal evolution of photogenerated excited states in the 2D WBDT COF thin film using remote-detected time-resolved PL measurements (RDTR PL). Combined with optical pump terahertz probe (OPTP) studies, we identified two diffusive species dominating the process at different time scales. Initially, short-lived free charge carriers diffuse almost temperature-independently before relaxing into bound states at a rate of 0.7 ps\textendash1. Supported by theoretical simulations, these long-lived bound states were identified as excitons. We directly accessed the lateral exciton diffusion within the oriented and crystalline film, revealing remarkably high diffusion coefficients of up to 4 cm2 s\textendash1 (200 K) and diffusion lengths of several hundreds of nanometers and across grain boundaries. Temperature-dependent exciton transport analysis showed contributions from both incoherent hopping and coherent band-like transport. In the transport model developed based on these findings, we discuss the complex impact of order and disorder on charge carrier diffusion within the WBDT COF thin film.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Sensitive Self-Driven Single-Component Organic Photodetector Based on Vapor-Deposited Small Molecules},

author = {J Wolansky and C Hoffmann and M Panhans and L C Winkler and F Talnack and S Hutsch and H Zhang and A Kirch and K M Yallum and H Friedrich and J Kublitski and F Gao and D Spoltore and S C B Mannsfeld and F Ortmann and N Banerji and K Leo and J Benduhn},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.202402834},

doi = {https://doi.org/10.1002/adma.202402834},

issn = {0935-9648},

year  = {2024},

date = {2024-12-12},

journal = {Advanced Materials},

volume = {36},

number = {50},

pages = {2402834},

abstract = {Abstract Typically, organic solar cells (OSCs) and photodetectors (OPDs) comprise an electron donating and accepting material to facilitate efficient charge carrier generation. This approach has proven successful in achieving high-performance devices but has several drawbacks for upscaling and stability. This study presents a fully vacuum-deposited single-component OPD, employing the neat oligothiophene derivative DCV2-5T in the photoactive layer. Free charge carriers are generated with an internal quantum efficiency of 20 % at zero bias. By optimizing the device structure, a very low dark current of 3.4 · 10−11 A cm−2 at −0.1 V is achieved, comparable to the dark current of state-of-the-art bulk heterojunction OPDs. This optimization results in specific detectivities of 1· 1013 Jones (based on noise measurements), accompanied by a fast photoresponse (f-3dB = 200 kHz) and a broad linear dynamic range (\> 150 dB). Ultrafast transient absorption spectroscopy unveils that charge carriers are already formed at very short time scales (\< 1 ps). The surprisingly efficient bulk charge generation mechanism is attributed to a strong electronic coupling of the molecular exciton and charge transfer states. This work demonstrates the very high performance of single-component OPDs and proves that this novel device design is a successful strategy for highly efficient, morphological stable and easily manufacturable devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Photons, Excitons, and Electrons in Covalent Organic Frameworks},

author = {D Bl\"{a}tte and F Ortmann and T Bein},

url = {https://doi.org/10.1021/jacs.3c14833},

doi = {10.1021/jacs.3c14833},

issn = {0002-7863},

year  = {2024},

date = {2024-11-27},

journal = {Journal of the American Chemical Society},

volume = {146},

number = {47},

pages = {32161-32205},

abstract = {Covalent organic frameworks (COFs) are created by the condensation of molecular building blocks and nodes to form two-dimensional (2D) or three-dimensional (3D) crystalline frameworks. The diversity of molecular building blocks with different properties and functionalities and the large number of possible framework topologies open a vast space of possible well-defined porous architectures. Besides more classical applications of porous materials such as molecular absorption, separation, and catalytic conversions, interest in the optoelectronic properties of COFs has recently increased considerably. The electronic properties of both the molecular building blocks and their linkage chemistry can be controlled to tune photon absorption and emission, to create excitons and charge carriers, and to use these charge carriers in different applications such as photocatalysis, luminescence, chemical sensing, and photovoltaics. In this Perspective, we will discuss the relationship between the structural features of COFs and their optoelectronic properties, starting with the building blocks and their chemical connectivity, layer stacking in 2D COFs, control over defects and morphology including thin film synthesis, exploring the theoretical modeling of structural, electronic, and dynamic features of COFs, and discussing recent intriguing applications with a focus on photocatalysis and photoelectrochemistry. We conclude with some remarks about present challenges and future prospects of this powerful architectural paradigm.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Direct visualization of the charge transfer state dynamics in dilute-donor organic photovoltaic blends},

author = {G J Moore and F G\"{u}nther and K M Yallum and M Causa’ and A Jungbluth and J R\'{e}hault and M Riede and F Ortmann and N Banerji},

url = {https://doi.org/10.1038/s41467-024-53694-4},

doi = {10.1038/s41467-024-53694-4},

issn = {2041-1723},

year  = {2024},

date = {2024-11-14},

journal = {Nature Communications},

volume = {15},

number = {1},

pages = {9851},

abstract = {The interconversion dynamics between charge transfer state charges (CTCs) and separated charges (SCs) is still an unresolved issue in the field of organic photovoltaics. Here, a transient absorption spectroscopy (TAS) study of a thermally evaporated small-molecule:fullerene system (α6T:C60) in different morphologies (dilute intermixed and phase separated) is presented. Spectral decomposition reveals two charge species with distinct absorption characteristics and different dynamics. Using time-dependent density functional theory, these species are identified as CTCs and SCs, where the spectral differences arise from broken symmetry in the charge transfer state that turns forbidden transitions into allowed ones. Based on this assignment, a kinetic model is formulated allowing the characterization of the charge generation, separation, and recombination mechanisms. We find that SCs are either formed directly from excitons within a few picoseconds or more slowly (~30\textendash80 ps) from reversible splitting of CTCs. These findings constitute the first unambiguous observation of spectrally resolved CTCs and SCs.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Comparison of Matrix Product State and Multiconfiguration Time-Dependent Hartree Methods for Nonadiabatic Dynamics of Exciton Dissociation},

author = {M F X Dorfner and D Brey and I Burghardt and F Ortmann},

url = {https://doi.org/10.1021/acs.jctc.4c00751},

doi = {10.1021/acs.jctc.4c00751},

issn = {1549-9618},

year  = {2024},

date = {2024-10-22},

journal = {Journal of Chemical Theory and Computation},

volume = {20},

number = {20},

pages = {8767-8781},

abstract = {The excited-state dynamics of organic molecules, molecular aggregates, and donor\textendashacceptor clusters is typically governed by the interplay of electronic excitations and, due to their flexibility and soft bonding, by the interaction with their vibrations. This interaction in these systems can be characterized by a few relevant electronic states that are coupled to numerous vibrational normal modes, encompassing a vast configurational space of the molecules. The full quantum simulation of these type of systems has been long dominated by the multiconfiguration time-dependent Hartree (MCTDH) approach and its multilayer variants, which are considered the gold standard in the presence of electron-vibration coupling with a large number of modes. Recently, also the matrix product state ansatz (MPS) with appropriate time-evolution schemes has been applied to these types of Hamiltonians. In this article, we provide a numerical comparison of excited-state dynamics between the MCTDH and MPS approaches for two electron-vibration coupled systems. Notably, we consider two models for exciton dissociation at a P3HT:PCBM heterojunction, comprising two electronic states and 100 vibrational modes, and 26 electronic states and 113 vibrational modes, respectively. While both methods agree very well for the first model, more pronounced deviations are found for the second model. We trace back the divergence between the methods to the different way entanglement is treated.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Engineering the electrostatic potential in a COF's pore by selecting quadrupolar building blocks and linkages},

author = {E-A Bittner and K Merkel and F Ortmann},

url = {https://doi.org/10.1038/s41699-024-00496-3},

doi = {10.1038/s41699-024-00496-3},

issn = {2397-7132},

year  = {2024},

date = {2024-09-04},

journal = {npj 2D Materials and Applications},

volume = {8},

number = {1},

pages = {58},

abstract = {The electrostatic potential within porous materials critically influences applications like gas storage, catalysis, sensors and semiconductor technology. Precise control of this potential in covalent organic frameworks (COFs) is essential for optimizing these applications. We propose a straightforward method to achieve this by employing electric quadrupolar building blocks. Our comprehensive models accurately reproduce the electrostatic potential in 2D-COFs, requiring only a few parameters that depend solely on local electrostatic properties, independent of the COF’s lattice structure and topology. This approach has been validated across various systems, including conjugated and non-conjugated building blocks with different symmetries. We explore single-layer, few-layer, and bulk systems, achieving changes in the potential which exceed one electronvolt. Stacking configurations such as eclipsed AA, serrated AA’, and inclined stacking all exhibit the tuning effect with minor variations. Finally, we discuss the impact of these potential manipulations on applications like ion and gas uptake.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Impact of heteroatoms and chemical functionalisation on crystal structure and carrier mobility of organic semiconductors},

author = {S Hutsch and F Ortmann},

url = {https://doi.org/10.1038/s41524-024-01397-1},

doi = {10.1038/s41524-024-01397-1},

issn = {2057-3960},

year  = {2024},

date = {2024-09-04},

journal = {npj Computational Materials},

volume = {10},

number = {1},

pages = {206},

abstract = {The substitution of heteroatoms and the functionalisation of molecules are established strategies in chemical synthesis. They target the precise tuning of the electronic properties of hydrocarbon molecules to improve their performance in various applications and increase their versatility. Modifications to the molecular structure often lead to simultaneous changes in the morphology such as different crystal structures. These changes can have a stronger and unpredictable impact on the targeted property. The complex relationships between substitution/functionalization in chemical synthesis and the resulting modifications of properties in thin films or crystals are difficult to predict and remain elusive. Here we address these effects for charge carrier transport in organic crystals by combining simulations of carrier mobilities with crystal structure prediction based on density functional theory and density functional tight binding theory. This enables the prediction of carrier mobilities based solely on the molecular structure and allows for the investigation of chemical modifications prior to synthesis and characterisation. Studying nine specific molecules with tetracene and rubrene as reference compounds along with their combined modifications of the molecular cores and additional functionalisations, we unveil systematic trends for the carrier mobilities of their polymorphs. The positive effect of phenyl groups that is responsible for the marked differences between tetracene and rubrene can be transferred to other small molecules such as NDT and NBT leading to a mobility increase by large factors of about five.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Hall transport in organic semiconductors},

author = {M Panhans and F Ortmann},

url = {https://link.aps.org/doi/10.1103/PhysRevB.110.125202},

doi = {10.1103/PhysRevB.110.125202},

year  = {2024},

date = {2024-09-03},

journal = {Physical Review B},

volume = {110},

number = {12},

pages = {125202},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Linear scaling approach for optical excitations using maximally localized Wannier functions},

author = {K Merkel and F Ortmann},

url = {https://dx.doi.org/10.1088/2515-7639/ad06cd},

doi = {10.1088/2515-7639/ad06cd},

issn = {2515-7639},

year  = {2023},

date = {2023-11-06},

journal = {Journal of Physics: Materials},

volume = {7},

number = {1},

pages = {015001},

abstract = {We present a theoretical method for calculating optical absorption spectra based on maximally localized Wannier functions, which is suitable for large periodic systems. For this purpose, we calculate the exciton Hamiltonian, which determines the Bethe\textendashSalpeter equation for the macroscopic polarization function and optical absorption characteristics. The Wannier functions are specific to each material and provide a minimal and therefore computationally convenient basis. Furthermore, their strong localization greatly improves the computational performance in two ways: first, the resulting Hamiltonian becomes very sparse and, second, the electron\textendashhole interaction terms can be evaluated efficiently in real space, where large electron\textendashhole distances are handled by a multipole expansion. For the calculation of optical spectra we employ the sparse exciton Hamiltonian in a time-domain approach, which scales linearly with system size. We demonstrate the method for bulk silicon\textemdashone of the most frequently studied benchmark systems\textemdashand envision calculating optical properties of systems with much larger and more complex unit cells, which are presently computationally prohibitive.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Band Structure Engineering in Highly Crystalline Organic Semiconductors},

author = {S-J Wang and S Hutsch and F Talnack and M Deconinck and S Huang and Z Zhang and A-L Hofmann and H Thiersch and H Kleemann and Y Vaynzof and S C B Mannsfeld and F Ortmann and K Leo},

url = {https://doi.org/10.1021/acs.chemmater.3c01934},

doi = {10.1021/acs.chemmater.3c01934},

issn = {0897-4756},

year  = {2023},

date = {2023-09-26},

journal = {Chemistry of Materials},

volume = {35},

number = {18},

pages = {7867-7874},

abstract = {Blending of semiconductors for controlling the energy levels (band structure engineering) is an important technique, in particular, for optoelectronic applications. The underlying physics is the delocalized Bloch states, which average over the potential landscape of the blend. For organic semiconductors, it has been shown that two quite different effects, the dielectric constant and electrostatic interaction between molecules, can be used to tune the energy gap and ionization energy of disordered and weakly crystalline organic semiconductor blends. It is so far not known whether the electronic delocalization in organic crystals with large bandwidths can contribute to the energy structure engineering of the blend in a way similar to that in inorganic semiconductors. Here, we investigate the growth of highly ordered organic thin-film blends with a similar chemical structure and show the effect of band structure engineering by spectroscopic methods. We rationalize the experimental results with comprehensive theoretical simulations, showing that the delocalization is a significant effect. Our work paves the way for engineering the band structure of highly ordered organic semiconductor thin films that can be tailored for the desired optoelectronic device application.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Directed exciton transport highways in organic semiconductors},

author = {K M\"{u}ller and K S Schellhammer and N Gr\"{a}\ssler and B Debnath and F Liu and Y Krupskaya and K Leo and M Knupfer and F Ortmann},

url = {https://doi.org/10.1038/s41467-023-41044-9},

doi = {10.1038/s41467-023-41044-9},

issn = {2041-1723},

year  = {2023},

date = {2023-09-12},

journal = {Nature Communications},

volume = {14},

number = {1},

pages = {5599},

abstract = {Exciton bandwidths and exciton transport are difficult to control by material design. We showcase the intriguing excitonic properties in an organic semiconductor material with specifically tailored functional groups, in which extremely broad exciton bands in the near-infrared-visible part of the electromagnetic spectrum are observed by electron energy loss spectroscopy and theoretically explained by a close contact between tightly packing molecules and by their strong interactions. This is induced by the donor\textendashacceptor type molecular structure and its resulting crystal packing, which induces a remarkable anisotropy that should lead to a strongly directed transport of excitons. The observations and detailed understanding of the results yield blueprints for the design of molecular structures in which similar molecular features might be used to further explore the tunability of excitonic bands and pave a way for organic materials with strongly enhanced transport and built-in control of the propagation direction.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Insight on charge-transfer regimes in electron-phonon coupled molecular systems via numerically exact simulations},

author = {M Panhans and S Hutsch and F Ortmann},

url = {https://doi.org/10.1038/s42005-023-01241-w},

doi = {10.1038/s42005-023-01241-w},

issn = {2399-3650},

year  = {2023},

date = {2023-05-31},

journal = {Communications Physics},

volume = {6},

number = {1},

pages = {125},

abstract = {Various simulation approaches exist to describe charge transport in organic solids, offering significantly different descriptions of the physics of electron-phonon coupling. This variety introduces method-dependent biases, which inevitably result in difficulties to interpret charge transport processes in a unified picture. Here, we combine numerical and analytical quantum approaches to investigate the charge-transfer dynamics in an unbiased framework. We unveil the fading of transient localisation and the formation of polarons in a broad range of vibrational frequencies and temperatures. By studying the joint electron-phonon dynamics from femtoseconds to nanoseconds, we identify three distinct charge-transport regimes: transient localisation, Soft Gating, and polaron transport. The dynamic transitions between such regimes are ruled by a buildup of the correlations between electronic motion and nuclei, which lead to the crossover between transient localisation and polaron transport. This transition is seamless at all temperatures and adiabaticities, even in the limit of low-frequency vibrational modes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Evolution of Length-Dependent Properties of Discrete n-Type Oligomers Prepared via Scalable Direct Arylation},

author = {R Matsidik and H Komber and M Brinkmann and K S Schellhammer and F Ortmann and M Sommer},

url = {https://doi.org/10.1021/jacs.3c00058},

doi = {10.1021/jacs.3c00058},

issn = {0002-7863},

year  = {2023},

date = {2023-04-19},

journal = {Journal of the American Chemical Society},

volume = {145},

number = {15},

pages = {8430-8444},

abstract = {Efficient organic electronic devices are fabricated from both small molecules and disperse polymers, but materials with characteristics in between remain largely unexplored. Here, we present a gram-scale synthesis for a series of discrete n-type oligomers comprising alternating naphthalene diimide (NDI) and bithiophene (T2). Using C\textendashH activation, discrete oligomers of type T2-(NDI-T2)n (n ≤ 7) and persistence lengths up to ∼10 nm are made. The absence of protection/deprotection reactions and the mechanistic nature of Pd-catalyzed C\textendashH activation allow one to produce symmetrically terminated species almost exclusively, which is key to the fast preparation, high yields, and the general success of the reaction pathway. The reaction scope includes different thiophene-based monomers, end-capping to yield NDI-(T2-NDI)n (n ≤ 8), and branching at T2 units by nonselective C\textendashH activation under certain conditions. We show how the optical, electronic, thermal, and structural properties depend on oligomer length along with a comparison to the disperse, polymeric analogue PNDIT2. From theory and experiments, we find that the molecular energy levels are not affected by chain length resulting from the strong donor\textendashacceptor system. Absorption maxima saturate for n = 4 in vacuum and for n = 8 in solution. Linear oligomers T2-(NDI-T2)n are highly crystalline with large melting enthalpies up to 33 J/g; NDI-terminated oligomers show reduced crystallinity, stronger supercooling, and more phase transitions. Branched oligomers and those with bulky thiophene comonomers are amorphous. Large oligomers exhibit similar packing characteristics compared to PNDIT2, making these oligomers ideal models to study length\textendashstructure\textendashfunction relationships at constant energy levels.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Understanding the electronic pi-system of 2D covalent organic frameworks with Wannier functions},

author = {K Merkel and J Greiner and F Ortmann},

url = {https://doi.org/10.1038/s41598-023-28285-w},

doi = {10.1038/s41598-023-28285-w},

issn = {2045-2322},

year  = {2023},

date = {2023-01-30},

journal = {Scientific Reports},

volume = {13},

number = {1},

pages = {1685},

abstract = {We investigate a family of hexagonal 2D covalent organic frameworks (COFs) with phenyl and biphenyl spacer units and different chemical linker species. Chemical trends are elucidated and attributed to microscopic properties of the $π$-electron-system spanned by atomic $$p_z$$-orbitals. We systematically investigate the electronic structure, delocalization of electronic states, effects of disorder, bond torsion, and doping, and correlate these with variable $π$-conjugation and nucleus-independent chemical shift (NICS) aromaticity. Molecular orbitals are obtained from maximally localized Wannier functions that have $σ$- and $π$-character, forming distinct $σ$- and $π$-bands for all valence states. The Wannier-orbital description goes beyond simple tight-binding models and enables a detailed understanding of the electronic topology, effective electronic coupling and delocalization. It is shown that a meaningful comparison between COFs with different chemical elements can only be made by examining the entire $π$-electron system, while a comparison of individual bands (e.g., bands near the Fermi energy) can be a insufficient to derive general design rules for linker and spacer monomer selection. We further identify delocalized states that are spread across tens or hundreds of pores of the 2D COFs and analyze their robustness against structural and energetic disorders like out-of-plane rotations of molecular fragments, different strength of energetic disorder and energetic shifts due to chemical doping.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Charge transport in single polymer fiber transistors in the sub 100 nm regime: temperature dependence and Coulomb blockade},

author = {J Lenz and M Statz and K Watanabe and T Taniguchi and F Ortmann and R T Weitz},

url = {https://iopscience.iop.org/article/10.1088/2515-7639/aca82f/meta},

doi = {10.1088/2515-7639/aca82f},

issn = {2515-7639},

year  = {2022},

date = {2022-12-15},

journal = {Journal of Physics: Materials},

abstract = {Even though charge transport in semiconducting polymers is of relevance for a number of potential applications in (opto-)electronic devices, the fundamental mechanism of how charges are transported through organic polymers that are typically characterized by a complex nanostructure is still open. One of the challenges which we address here, is how to gain controllable experimental access to charge transport at the sub-100 nm lengthscale. To this end charge transport in single poly(diketopyrrolopyrrole-terthiophene) fiber transistors, employing two different solid gate dielectrics, a hybrid Al2O3/self-assembled monolayer and hexagonal boron nitride, is investigated in the sub-50 nm regime using electron-beam contact patterning. The electrical characteristics exhibit near ideal behavior at room temperature which demonstrates the general feasibility of the nanoscale contacting approach, even though the channels are only a few nanometers in width. At low temperatures, we observe nonlinear behavior in the current\textendashvoltage characteristics in the form of Coulomb diamonds which can be explained by the formation of an array of multiple quantum dots at cryogenic temperatures.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Charge carrier mobilities of organic semiconductors: ab initio simulations with mode-specific treatment of molecular vibrations},

author = {S Hutsch and M Panhans and F Ortmann},

url = {https://doi.org/10.1038/s41524-022-00915-3},

doi = {10.1038/s41524-022-00915-3},

issn = {2057-3960},

year  = {2022},

date = {2022-11-10},

journal = {npj Computational Materials},

volume = {8},

number = {1},

pages = {228},

abstract = {The modeling of charge transport in organic semiconductors usually relies on the treatment of molecular vibrations by assuming a certain limiting case for all vibration modes, such as the dynamic limit in polaron theory or the quasi-static limit in transient localization theory. These opposite limits are each suitable for only a subset of modes. Here, we present a model that combines these different approaches. It is based on a separation of the vibrational spectrum and a quantum-mechanical treatment in which the slow modes generate a disorder landscape, while the fast modes generate polaron band narrowing. We apply the combined method to 20 organic crystals, including prototypical acenes, thiophenes, benzothiophenes, and their derivatives. Their mobilities span several orders of magnitude and we find a close agreement to the experimental mobilities. Further analysis reveals clear correlations to simple mobility predictors and a combination of them can be used to identify high-mobility materials.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Interplay of band occupation, localization, and polaron renormalization for electron transport in molecular crystals: Naphthalene as a case study},

author = {K Merkel and M Panhans and S Hutsch and F Ortmann},

url = {https://link.aps.org/doi/10.1103/PhysRevB.105.165136},

doi = {10.1103/PhysRevB.105.165136},

year  = {2022},

date = {2022-04-19},

journal = {Physical Review B},

volume = {105},

number = {16},

pages = {165136},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Highly efficient modulation doping: A path toward superior organic thermoelectric devices},

author = {S-J Wang and M Panhans and I Lashkov and H Kleemann and F Caglieris and D Becker-Koch and J Vahland and E Guo and S Huang and Y Krupskaya and Y Vaynzof and B B\"{u}chner and F Ortmann and K Leo},

url = {https://www.science.org/doi/abs/10.1126/sciadv.abl9264},

doi = {doi:10.1126/sciadv.abl9264},

year  = {2022},

date = {2022-03-30},

journal = {Science Advances},

volume = {8},

number = {13},

pages = {eabl9264},

abstract = {We investigate the charge and thermoelectric transport in modulation-doped large-area rubrene thin-film crystals with different crystal phases. We show that modulation doping allows achieving superior doping efficiencies even for high doping densities, when conventional bulk doping runs into the reserve regime. Modulation-doped orthorhombic rubrene achieves much improved thermoelectric power factors, exceeding 20 μW m−1 K−2 at 80°C. Theoretical studies give insight into the energy landscape of the heterostructures and its influence on qualitative trends of the Seebeck coefficient. Our results show that modulation doping together with high-mobility crystalline organic semiconductor films is a previosly unexplored strategy for achieving high-performance organic thermoelectrics. Highly efficient modulation doping is realized in ordered organic semiconductors enabling high performance thermoelectric devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Thermal behavior and polymorphism of 2,9-didecyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene thin films},

author = {F Talnack and S Hutsch and M Bretschneider and Y Krupskaya and B B\"{u}chner and M Malfois and M Hambsch and F Ortmann and S C B Mannsfeld},

url = {http://dx.doi.org/10.1039/D1ME00153A},

doi = {10.1039/D1ME00153A},

year  = {2022},

date = {2022-01-31},

journal = {Molecular Systems Design \& Engineering},

volume = {7},

number = {5},

pages = {507-519},

abstract = {The ability of numerous organic molecules to adopt different crystal structures without changing their chemical structure is called polymorphism which has gained interest in recent years due to the influence it has on the solid-state properties of organic materials, e.g. charge transport in organic semiconductors. Here we present a new polymorphic crystal structure of the p-type small molecule semiconductor 2,9-didecyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C10-DNTT). The polymorphic transition is observed during heating the films over 400 K and investigated by in situ cross-polarized optical microscopy (CPOM) and in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. From these measurements, we refine the thin-film crystal structure of both the low temperature and high temperature polymorphs. We further analyze the thermal expansion of both polymorphs and perform density-functional theory (DFT) calculations to trace back the anisotropic thermal expansion to anisotropic molecular interactions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Ultrafast carrier dynamics at organic donor\textendashacceptor interfaces\textemdasha quantum-based assessment of the hopping model},

author = {M F X Dorfner and S Hutsch and R Borrelli and M F Gelin and F Ortmann},

url = {http://dx.doi.org/10.1088/2515-7639/ac442b},

doi = {10.1088/2515-7639/ac442b},

issn = {2515-7639},

year  = {2022},

date = {2022-01-10},

journal = {Journal of Physics: Materials},

volume = {5},

number = {2},

pages = {024001},

abstract = {We investigate the charge transfer dynamics of photogenerated excitons at the donor\textendashacceptor interface of an organic solar cell blend under the influence of molecular vibrations. This is examined using an effective Hamiltonian, parametrized by density functional theory calculations, to describe the full quantum behaviour of the relevant molecular orbitals, which are electronically coupled with each other and coupled to over 100 vibrations (via Holstein coupling). This electron\textendashphonon system is treated in a numerically quasi-exact fashion using the matrix-product-state (MPS) ansatz. We provide insight into different mechanisms of charge separation and their relation to the electronic driving energy for the separation process. We find ultrafast electron transfer, which for small driving energy is dominated by kinetic processes and at larger driving energies by dissipative phonon emission connected to the prevalent vibration modes. Using this fully quantum mechanical model we perform a benchmark comparison to a recently developed semi-classical hopping approach, which treats the hopping and vibration time scales consistently. We find qualitatively and quantitatively good agreement between the results of the sophisticated MPS based quantum dynamics and the simple and fast time-consistent-hopping approach.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Time-consistent hopping transport with vibration-mode-resolved electron-phonon couplings},

author = {S Hutsch and M Panhans and F Ortmann},

url = {https://link.aps.org/doi/10.1103/PhysRevB.104.054306},

doi = {10.1103/PhysRevB.104.054306},

year  = {2021},

date = {2021-08-25},

journal = {Physical Review B},

volume = {104},

number = {5},

pages = {054306},

abstract = {Charge transport in organic semiconductors is affected by the complex interaction between charge carriers and molecular vibrations. A common way to treat the molecular vibrations in hopping approaches is by condensing them into a single analytical parameter, the reorganization energy. In contrast, here we present a nonadiabatic hopping transport approach that avoids this approximation by dividing the vibrational spectrum of organic molecules into three distinct analytical classes, namely the quasistatic, low-frequency dynamic, and high-frequency dynamic modes. The quasistatic and dynamic regimes are separated time consistently with respect to the timescale of the hopping events, which results in charge transfer events driven by a set of strongly coupling driving modes. Using these time-consistent hopping rates, we compute the charge carrier mobilities for a set of hopping transport materials and a control set of band-transport materials and compare them to experimental values. The resulting mobilities are consistent for both sets by showing similar values for the hopping transport materials and lower values for the control set of band-transport materials due to the absence of coherent transport contributions. We further study other popular hopping approaches such as the Marcus theory and the Levich-Jortner theory and observe substantial inconsistencies for them.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Short Excited‐State Lifetimes Mediate Charge‐Recombination Losses in Organic Solar Cell Blends with Low Charge‐Transfer Driving Force},

author = {R Shivhare and G J Moore and A Hofacker and S Hutsch and Y Zhong and M Hambsch and T Erdmann and A Kiriy and S C Mannsfeld and F Ortmann},

doi = {https://doi.org/10.1002/adma.202101784},

issn = {0935-9648},

year  = {2021},

date = {2021-08-15},

urldate = {2021-08-15},

journal = {Advanced Materials},

pages = {2101784},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Efficient Time-Domain Approach for Linear Response Functions},

author = {M Panhans and F Ortmann},

url = {https://link.aps.org/doi/10.1103/PhysRevLett.127.016601},

doi = {10.1103/PhysRevLett.127.016601},

year  = {2021},

date = {2021-06-29},

journal = {Physical Review Letters},

volume = {127},

number = {1},

pages = {016601},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Band gap engineering in blended organic semiconductor films based on dielectric interactions},

author = {K Ortstein and S Hutsch and M Hambsch and K Tvingstedt and B Wegner and J Benduhn and J Kublitski and M Schwarze and S Schellhammer and F Talnack and A Vogt and P B\"{a}uerle and N Koch and S C B Mannsfeld and H Kleemann and F Ortmann and K Leo},

url = {https://doi.org/10.1038/s41563-021-01025-z},

doi = {10.1038/s41563-021-01025-z},

issn = {1476-4660},

year  = {2021},

date = {2021-06-10},

urldate = {2021-06-10},

journal = {Nature Materials},

abstract = {Blending organic molecules to tune their energy levels is currently being investigated as an approach to engineer the bulk and interfacial optoelectronic properties of organic semiconductors. It has been proven that the ionization energy and electron affinity can be equally shifted in the same direction by electrostatic effects controlled by blending similar halogenated derivatives with different energetics. Here we show that the energy gap of organic semiconductors can also be tuned by blending. We use oligothiophenes with different numbers of thiophene rings as an example and investigate their structure and electronic properties. Photoelectron spectroscopy and inverse photoelectron spectroscopy show tunability of the single-particle gap, with the optical gaps showing similar, but smaller, effects. Theoretical analysis shows that this tuning is mainly caused by a change in the dielectric constant with blend ratio. Further studies will explore the practical impact of this energy-level engineering strategy for optoelectronic devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}