Abstract
Organic semiconductors, which serve as the active component in devices, such as solar cells, light-emitting diodes and field-effect transistors1, often exhibit highly unipolar charge transport, meaning that they predominantly conduct either electrons or holes. Here, we identify an energy window inside which organic semiconductors do not experience charge trapping for device-relevant thicknesses in the range of 100 to 300 nm, leading to trap-free charge transport of both carriers. When the ionization energy of a material surpasses 6 eV, hole trapping will limit the hole transport, whereas an electron affinity lower than 3.6 eV will give rise to trap-limited electron transport. When both energy levels are within this window, trap-free bipolar charge transport occurs. Based on simulations, water clusters are proposed to be the source of hole trapping. Organic semiconductors with energy levels situated within this energy window may lead to optoelectronic devices with enhanced performance. However, for blue-emitting light-emitting diodes, which require an energy gap of 3 eV, removing or disabling charge traps will remain a challenge.
This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
Data availability
Experimental data are available from the corresponding author upon reasonable request.
References
Coropceanu, V. et al. Charge transport in organic semiconductors. Chem. Rev. 107, 926–952 (2007).
Tang, M. L., Reichardt, A. D., Wei, P. & Bao, Z. Correlating carrier type with frontier molecular orbital energy levels in organic thin film transistors of functionalized acene derivatives. J. Am. Chem. Soc. 131, 5264–5273 (2009).
Chua, L.-L. et al. General observation of N-type field-effect behaviour in organic semiconductors. Nature 434, 194–199 (2005).
Nicolai, H. T. et al. Unification of trap-limited electron transport in semiconducting polymers. Nat. Mater. 11, 882–887 (2012).
Kotadiya, N. B. et al. Universal strategy for ohmic hole injection into organic semiconductors with high ionization energies. Nat. Mater. 17, 329–334 (2018).
Mott, S. N. F. & Gurney, R. W. Electronic Processes in Ionic Crystals 2nd edn (Clarendon Press, 1948).
Mark, P. & Helfrich, W. Space‐charge‐limited currents in organic crystals. J. Appl. Phys. 33, 205–215 (1962).
Kotadiya, N. B., Blom, P. W. M. & Wetzelaer, G. A. H. Trap-free space-charge-limited hole transport in a fullerene derivative. Phys. Rev. Appl. 11, 024069 (2019).
Wetzelaer, G.-J. A. H. et al. Asymmetric electron and hole transport in a high-mobility n-type conjugated polymer. Phys. Rev. B 86, 165203 (2012).
Nicolai, H. T. et al. Space-charge-limited hole current in poly(9,9-dioctylfluorene) diodes. Appl. Phys. Lett. 96, 172107 (2010).
Wetzelaer, G. A. H. & Blom, P. W. M. Ohmic current in organic metal-insulator-metal diodes revisited. Phys. Rev. B 89, 241201 (2014).
Blom, P. W. M., de Jong, M. J. M. & Vleggaar, J. J. M. Electron and hole transport in poly(p‐phenylene vinylene) devices. Appl. Phys. Lett. 68, 3308–3310 (1996).
Rohloff, R., Kotadiya, N. B., Crăciun, N. I., Blom, P. W. M. & Wetzelaer, G. A. H. Electron and hole transport in the organic small molecule α-NPD. Appl. Phys. Lett. 110, 073301 (2017).
Kotadiya, N. B. et al. Rigorous characterization and predictive modeling of hole transport in amorphous organic semiconductors. Adv. Electron. Mater. 4, 1800366 (2018).
Karki, A. et al. Unifying energetic disorder from charge transport and band bending in organic semiconductors. Adv. Funct. Mater. 29, 1901109 (2019).
Vissenberg, M. C. J. M. & Blom, P. W. M. Transient hole transport in poly(-p-phenylene vinylene) LEDs. Synth. Met. 102, 1053–1054 (1999).
Torabi, S. et al. Strategy for enhancing the dielectric constant of organic semiconductors without sacrificing charge carrier mobility and solubility. Adv. Funct. Mater. 25, 150–157 (2015).
Seemann, A. et al. Reversible and irreversible degradation of organic solar cell performance by oxygen. Solar Energy 85, 1238–1249 (2011).
Nayak, P. K., Rosenberg, R., Barnea-Nehoshtan, L. & Cahen, D. O2 and organic semiconductors: electronic effects. Org. Electron. 14, 966–972 (2013).
Zhuo, J.-M. et al. Direct spectroscopic evidence for a photodoping mechanism in polythiophene and poly(bithiophene-alt-thienothiophene) organic semiconductor thin films involving oxygen and sorbed moisture. Adv. Mater. 21, 4747–4752 (2009).
Nikolka, M. et al. High operational and environmental stability of high-mobility conjugated polymer field-effect transistors through the use of molecular additives. Nat. Mater. 16, 356–362 (2017).
Zuo, G., Linares, M., Upreti, T. & Kemerink, M. General rule for the energy of water-induced traps in organic semiconductors. Nat. Mater. 18, 588–593 (2019).
Page, R. H., Larkin, R. J., Shen, Y. R. & Lee, Y. T. High‐resolution photoionization spectrum of water molecules in a supersonic beam. J. Chem. Phys. 88, 2249–2263 (1988).
Tonkyn, R. G., Winniczek, J. W. & White, M. G. Rotationally resolved photoionization of O2+ near threshold. Chem. Phys. Lett. 164, 137–142 (1989).
de Leeuw, D. M., Simenon, M. M. J., Brown, A. R. & Einerhand, R. E. F. Stability of n-type doped conducting polymers and consequences for polymeric microelectronic devices. Synth. Met. 87, 53–59 (1997).
Tanase, C., Meijer, E. J., Blom, P. W. M. & de Leeuw, D. M. Unification of the hole transport in polymeric field-effect transistors and light-emitting diodes. Phys. Rev. Lett. 91, 216601 (2003).
Uoyama, H., Goushi, K., Shizu, K., Nomura, H. & Adachi, C. Highly efficient organic light-emitting diodes from delayed fluorescence. Nature 492, 234–238 (2012).
Jorgensen, W. L. & Tirado-Rives, J. The OPLS [optimized potentials for liquid simulations] potential functions for proteins, energy minimizations for crystals of cyclic peptides and crambin. J. Am. Chem. Soc. 110, 1657–1666 (1988).
Jorgensen, W. L., Maxwell, D. S. & Tirado-Rives, J. Development and testing of the OPLS all-atom force field on conformational energetics and properties of organic liquids. J. Am. Chem. Soc. 118, 11225–11236 (1996).
Jorgensen, W. L. & Tirado-Rives, J. Potential energy functions for atomic-level simulations of water and organic and biomolecular systems. Proc. Natl Acad. Sci. USA 102, 6665–6670 (2005).
McDonald, N. A. & Jorgensen, W. L. Development of an all-atom force field for heterocycles. Properties of liquid pyrrole, furan, diazoles, and oxazoles. J. Phys. Chem. B 102, 8049–8059 (1998).
Poelking, C. et al. Characterization of charge-carrier transport in semicrystalline polymers: electronic couplings, site energies, and charge-carrier dynamics in poly(bithiophene-alt-thienothiophene) [PBTTT]. J. Phys. Chem. C 117, 1633–1640 (2013).
Poelking, C. & Andrienko, D. Effect of polymorphism, regioregularity and paracrystallinity on charge transport in poly(3-hexyl-thiophene) [P3HT] nanofibers. Macromolecules 46, 8941–8956 (2013).
Breneman, C. M. & Wiberg, K. B. Determining atom-centered monopoles from molecular electrostatic potentials. The need for high sampling density in formamide conformational analysis. J. Comput. Chem. 11, 361–373 (1990).
Berendsen, H. J. C., Grigera, J. R. & Straatsma, T. P. The missing term in effective pair potentials. J. Phys. Chem. 91, 6269–6271 (1987).
Bussi, G., Donadio, D. & Parrinello, M. Canonical sampling through velocity rescaling. J. Chem. Phys. 126, 014101 (2007).
Berendsen, H. J. C., Postma, J. P. M., Gunsteren, W. F., van; DiNola, A. & Haak, J. R. Molecular dynamics with coupling to an external bath. J. Chem. Phys. 81, 3684–3690 (1984).
Pronk, S. et al. GROMACS 4.5: a high-throughput and highly parallel open source molecular simulation toolkit. Bioinformatics 29, 845–854 (2013).
Van Der Spoel, D. et al. GROMACS: fast, flexible, and free. J. Comput. Chem. 26, 1701–1718 (2005).
Poelking, C. & Andrienko, D. Long-range embedding of molecular ions and excitations in a polarizable molecular environment. J. Chem. Theory Comput. 12, 4516–4523 (2016).
Poelking, C. & Andrienko, D. Design rules for organic donor-acceptor heterojunctions: pathway for charge splitting and detrapping. J. Am. Chem. Soc. 2015, 6320–6326.
Poelking, C. et al. Impact of mesoscale order on open-circuit voltage in organic solar cells. Nat. Mater. 14, 434–439 (2015).
D’Avino, G. et al. Electrostatic phenomena in organic semiconductors: fundamentals and implications for photovoltaics. J. Phys.: Condens. Matter 28, 433002 (2016).
Frisch, M. J. et al. Gaussian 16 Revision B.01 (Gaussian, Inc., 2016).
Thole, B. T. Molecular polarizabilities calculated with a modified dipole interaction. Chem. Phys. 59, 341–350 (1981).
Van Duijnen, P. Th & Swart, M. Molecular and atomic polarizabilities: Thole’s model revisited. J. Phys. Chem. A 102, 2399–2407 (1998).
Stone, A. J. Distributed multipole analysis—stability for large basis sets. J. Chem. Theory Comput. 1, 1128–1132 (2005).
Ruehle, V. et al. Microscopic simulations of charge transport in disordered organic semiconductors. J. Chem. Theory Comput. 7, 3335–3345 (2011).
Acknowledgements
The authors thank C. Bauer, M. Beuchel, Hs-J. Guttmann, F. Keller and V. Maus for technical support and Y. Ie for the synthesis of 4CzIPN. This project has received funding from the European Union Horizon 2020 research and innovation programme under grant agreement no. 646176 (EXTMOS) and no. 646259 (MOSTOPHOS). D.A. thanks the BMBF grant InterPhase (grant no. FKZ 13N13661).
Author information
Authors and Affiliations
Contributions
G.A.H.W. proposed the project. N.B.K. carried out sample preparation and electrical measurements. G.A.H.W. and N.B.K. analysed the experimental data. A.M. and D.A. devised and performed molecular-dynamics simulations. G.A.H.W., P.W.M.B. and D.A. supervised the project and wrote the manuscript, with input from N.B.K. and A.M.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Additional information
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information
Supplementary Information
Supplementary materials, Supplementary Figs. 1–15, Supplementary Refs. 1–29
Rights and permissions
About this article
Cite this article
Kotadiya, N.B., Mondal, A., Blom, P.W.M. et al. A window to trap-free charge transport in organic semiconducting thin films. Nat. Mater. 18, 1182–1186 (2019). https://doi.org/10.1038/s41563-019-0473-6
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41563-019-0473-6
This article is cited by
-
Inverted device architecture for high efficiency single-layer organic light-emitting diodes with imbalanced charge transport
Nature Communications (2024)
-
Water binding and hygroscopicity in π-conjugated polyelectrolytes
Nature Communications (2023)
-
Elimination of charge-carrier trapping by molecular design
Nature Materials (2023)
-
Large-bandgap organic semiconductors with trap-free charge transport
Nature Materials (2023)
-
Chemical doping to control the in-situ formed doping structure in light-emitting electrochemical cells
Scientific Reports (2023)