Molecular parameters responsible for thermally activated transport in doped organic semiconductors

Schwarze, Martin; Gaul, Christopher; Scholz, Reinhard; Bussolotti, Fabio; Hofacker, Andreas; Schellhammer, Karl Sebastian; Nell, Bernhard; Naab, Benjamin D.; Bao, Zhenan; Spoltore, Donato; Vandewal, Koen; Widmer, Johannes; Kera, Satoshi; Ueno, Nobuo; Ortmann, Frank; Leo, Karl

doi:10.1038/s41563-018-0277-0

Cited by 154 publications

(228 citation statements)

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“…The intentional introduction of molecular dopants has been used extensively to alter the charge transport properties of organic semiconductors, particularly in the area of organic thin‐film transistors (OTFTs) for which some of the highest carrier mobilities have been achieved via this method 6–9. Molecular doping relies on charge transfer interaction(s) between the dopant and the host semiconductor, which ultimately results in formation of free carriers 10,11. Recent studies have shown that molecular doping may, under certain conditions, induce multiple synergistic effects including microstructural changes to the host semiconductor and drastic improvement in charge carrier transport 6,8,9.…”

Section: Summary Of Operating Parameters Of Solar Cells Based On Pm6:mentioning

confidence: 99%

17.1% Efficient Single‐Junction Organic Solar Cells Enabled by n‐Type Doping of the Bulk‐Heterojunction

et al. 2020

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Molecular doping is often used in organic semiconductors to tune their (opto)electronic properties. Despite its versatility, however, its application in organic photovoltaics (OPVs) remains limited and restricted to p‐type dopants. In an effort to control the charge transport within the bulk‐heterojunction (BHJ) of OPVs, the n‐type dopant benzyl viologen (BV) is incorporated in a BHJ composed of the donor polymer PM6 and the small‐molecule acceptor IT‐4F. The power conversion efficiency (PCE) of the cells is found to increase from 13.2% to 14.4% upon addition of 0.004 wt% BV. Analysis of the photoactive materials and devices reveals that BV acts simultaneously as n‐type dopant and microstructure modifier for the BHJ. Under optimal BV concentrations, these synergistic effects result in balanced hole and electron mobilities, higher absorption coefficients and increased charge‐carrier density within the BHJ, while significantly extending the cells' shelf‐lifetime. The n‐type doping strategy is applied to five additional BHJ systems, for which similarly remarkable performance improvements are obtained. OPVs of particular interest are based on the ternary PM6:Y6:PC71BM:BV(0.004 wt%) blend for which a maximum PCE of 17.1%, is obtained. The effectiveness of the n‐doping strategy highlights electron transport in NFA‐based OPVs as being a key issue.

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Section: Summary Of Operating Parameters Of Solar Cells Based On Pm6:mentioning

confidence: 99%

17.1% Efficient Single‐Junction Organic Solar Cells Enabled by n‐Type Doping of the Bulk‐Heterojunction

et al. 2020

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“…The physical origin of this thermal activation energy E a is still under debate. Very recently, Schwartze et al have established that charge transport is controlled by the properties of host‐dopant integer charge‐transfer complexes (ICTCs) in efficiently doped organic semiconductors . Coulomb binding energy of ICTCs limits charge transport at low doping concentration.…”

Section: Charge Transportmentioning

confidence: 99%

“…At high doping concentration, E a recorded for a same matrix but with different dopants converge to a single value that is matrix dependent. Noteworthy is the fact that the matrix of C 60 2 with various dopants exhibits the lowest activation energies E a < 100 meV and the highest conductivity of electrons σ e on the order of 10 S cm −1 . This likely denotes the ability of fullerene to accommodate smaller dopant molecules within its crystal lattice but also to distribute charges over a large number of first neighbors due to electronic couplings extending in three dimensions.…”

Section: Charge Transportmentioning

confidence: 99%

Molecular Semiconductors for Logic Operations: Dead‐End or Bright Future?

et al. 2020

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The field of organic electronics has been prolific in the last couple of years, leading to the design and synthesis of several molecular semiconductors presenting a mobility in excess of 10 cm2 V−1 s−1. However, it is also started to recently falter, as a result of doubtful mobility extractions and reduced industrial interest. This critical review addresses the community of chemists and materials scientists to share with it a critical analysis of the best performing molecular semiconductors and of the inherent charge transport physics that takes place in them. The goal is to inspire chemists and materials scientists and to give them hope that the field of molecular semiconductors for logic operations is not engaged into a dead end. To the contrary, it offers plenty of research opportunities in materials chemistry.

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“…It is worth noting that the temperature dependence of conductivity in hot‐cast sample shows a sharp transition at ≈ 280 K, corresponding to the critical point for the trapping/activation of carriers in the in‐gap state at boundaries . According to the Nernst−Einstein equation

σ (T) = \frac{σ_{0}}{T} exp (\frac{- E_{a}}{k T})

we could derive an activation energy E a = 60 meV by fitting ln( σT ) in the temperature range of 77–300 K (Figure S6, Supporting Information), indicating that the in‐gap state has the feature of shallow traps and is slightly lower that the band‐gap state in the energy level alignment …”

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confidence: 99%

Grain Boundary Enhanced Photoluminescence Anisotropy in Two‐Dimensional Hybrid Perovskite Films

Wang

Tang

Wang

et al. 2020

Advanced Optical Materials

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As a promising luminescent material, the two-dimensional (2D) perovskite exhibits efficient and tunable photoluminescence due to its naturally self-assembled multiple quantum well structure and consequently large exciton binding energy. [20] The structural stability of 2D perovskites over their three-dimensional (3D) counterpart, owing to the hydrophobic nature of organic barriers and the van der Waals interaction of neighboring layers, has motivated further studies to engineer these layered structures and enhance their properties. [7,13,21] The crystal growth of 2D perovskite is usually parallel to the substrate, leading to a preferential orientation of layered structures in the polycrystalline film. [22,23] The structural anisotropy brings in not only significant difference between in-plane and out-of-plane conductivities [24] but also the unique emission performance at different angle. [25] In this case, the grain boundaries could break the local structural symmetry for dipole transitions, [26][27][28] and influence the anisotropic property of photoluminescence through the emissive in-gap state. Moreover, the interplay between in-gap state and band-gap state provides possibilities in developing bi-directionally controlled light emission from 2D perovskite films.In this work, we investigated the in-gap state related to grain boundaries and observed an significant enhancement of photoluminescence anisotropy from the (PEA) 2 PbI 4 (PEA is phenethylamine) films by reducing the grain size via hotcasting method. [29] The preparation temperature can change the morphology of 2D perovskite films and thus control the density of in-gap state, which is characterized by measuring the photoconductivity as the carrier dissociation is facilitated by grain boundaries. The photoluminescence of in-gap state shows an ≈20 nm red-shift compared with that of band-gap state, and more interestingly, is spatially anisotropic meaning that the light intensity is strongly dependent on the collection angle. The grain boundaries are found to enhance the in-gap emission and consequently bring the photoluminescence anisotropy from (PEA) 2 PbI 4 films. The origin of photoluminescence anisotropy is that the transition dipole moment of in-gap state is perpendicular to that of band-gap state, revealed by measuring the light polarization of photoluminescence bands.The (PEA) 2 PbI 4 polycrystalline films were prepared by a spin-casting method (see details in Supporting Information). The substrate was pre-heated to facilitate the solvent evaporation and thus the crystallization process during spin-casting, asThe boundaries between crystalline grains in hybrid perovskite films are beneficial for carrier dissociation, and may also serve as recombination centers to alter the photoluminescence property. Herein, it is shown that the grain boundaries can significantly enhance the anisotropy of photoluminescence from two-dimensional (2D) hybrid perovskite films. The measurement of carrier densities shows that the grain boundaries generate an in-gap state, ...

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Molecular parameters responsible for thermally activated transport in doped organic semiconductors

Cited by 154 publications

References 55 publications

17.1% Efficient Single‐Junction Organic Solar Cells Enabled by n‐Type Doping of the Bulk‐Heterojunction

17.1% Efficient Single‐Junction Organic Solar Cells Enabled by n‐Type Doping of the Bulk‐Heterojunction

Molecular Semiconductors for Logic Operations: Dead‐End or Bright Future?

Grain Boundary Enhanced Photoluminescence Anisotropy in Two‐Dimensional Hybrid Perovskite Films

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