Orientation dependent molecular electrostatics drives efficient charge generation in homojunction organic solar cells.
Journal
Nature communications
ISSN: 2041-1723
Titre abrégé: Nat Commun
Pays: England
ID NLM: 101528555
Informations de publication
Date de publication:
15 Sep 2020
15 Sep 2020
Historique:
received:
10
05
2020
accepted:
21
08
2020
entrez:
16
9
2020
pubmed:
17
9
2020
medline:
17
9
2020
Statut:
epublish
Résumé
Organic solar cells usually utilise a heterojunction between electron-donating (D) and electron-accepting (A) materials to split excitons into charges. However, the use of D-A blends intrinsically limits the photovoltage and introduces morphological instability. Here, we demonstrate that polycrystalline films of chemically identical molecules offer a promising alternative and show that photoexcitation of α-sexithiophene (α-6T) films results in efficient charge generation. This leads to α-6T based homojunction organic solar cells with an external quantum efficiency reaching up to 44% and an open-circuit voltage of 1.61 V. Morphological, photoemission, and modelling studies show that boundaries between α-6T crystalline domains with different orientations generate an electrostatic landscape with an interfacial energy offset of 0.4 eV, which promotes the formation of hybridised exciton/charge-transfer states at the interface, dissociating efficiently into free charges. Our findings open new avenues for organic solar cell design where material energetics are tuned through molecular electrostatic engineering and mesoscale structural control.
Identifiants
pubmed: 32934236
doi: 10.1038/s41467-020-18439-z
pii: 10.1038/s41467-020-18439-z
pmc: PMC7494863
doi:
Types de publication
Journal Article
Langues
eng
Sous-ensembles de citation
IM
Pagination
4617Subventions
Organisme : EC | EU Framework Programme for Research and Innovation H2020 | H2020 Priority Excellent Science | H2020 European Research Council (H2020 Excellent Science - European Research Council)
ID : 639750
Organisme : EC | EU Framework Programme for Research and Innovation H2020 | H2020 Priority Excellent Science | H2020 European Research Council (H2020 Excellent Science - European Research Council)
ID : 864625
Références
Reucroft, P. J., Takahashi, K. & Ullal, H. Theoretical efficiency in an organic photovoltaic energy conversion system. Appl. Phys. Lett. 25, 664–666 (1974).
Yu, G., Gao, J., Hummelen, J. C., Wudl, F. & Heeger, A. J. Polymer photovoltaic cells: enhanced efficiencies via a network of internal donor-acceptor heterojunctions. Science 270, 1789–1791 (1995).
Vandewal, K. et al. Efficient charge generation by relaxed charge-transfer states at organic interfaces. Nat. Mater. 13, 63–68 (2014).
pubmed: 24240240
Kurpiers, J. et al. Probing the pathways of free charge generation in organic bulk heterojunction solar cells. Nat. Commun. 9, 1–11 (2018).
Liu, Q. et al. 18% Efficiency organic solar cells. Sci. Bull. 65, 272–275 (2020).
Hou, J., Inganäs, O., Friend, R. H. & Gao, F. Organic solar cells based on non-fullerene acceptors. Nat. Mater. 17, 119–128 (2018).
pubmed: 29358765
Kwon, S. et al. Effect of processing additives on organic photovoltaics: recent progress and future prospects. Adv. Energy Mater. 7, 1601496 (2017).
Kraner, S. et al. Dielectric function of a poly(benzimidazobenzophenanthroline) ladder polymer. Phys. Rev. B 91, 195202 (2015).
Armin, A. et al. Engineering dielectric constants in organic semiconductors. J. Mater. Chem. C. 5, 3736–3747 (2017).
Vandewal, K., Benduhn, J. & Nikolis, V. C. How to determine optical gaps and voltage losses in organic photovoltaic materials. Sustain. Energy Fuels 2, 538–544 (2018).
Terao, Y., Sasabe, H. & Adachi, C. Correlation of hole mobility, exciton diffusion length, and solar cell characteristics in phthalocyanine/fullerene organic solar cells. Appl. Phys. Lett. 90, 103515 (2007).
Menke, S. M., Luhman, W. A. & Holmes, R. J. Tailored exciton diffusion in organic photovoltaic cells for enhanced power conversion efficiency. Nat. Mater. 12, 152–157 (2013).
pubmed: 23142837
Roncali, J. & Grosu, I. The dawn of single material organic solar cells. Adv. Sci. 6, 1801026 (2019).
Zhang, Y. et al. High-efficient charge generation in single-donor-component-based p-i-n structure organic solar cells. Sol. RRL 4, 1–9 (2020).
Tautz, R. et al. Structural correlations in the generation of polaron pairs in low-bandgap polymers for photovoltaics. Nat. Commun. 3, 970 (2012).
pubmed: 22828630
Cnops, K. et al. 8.4% Efficient fullerene-free organic solar cells exploiting long-range exciton energy transfer. Nat. Commun. 5, 1–6 (2014).
Crone, B. et al. Large-scale complementary integrated circuits based on organic transistors. Nature 403, 521–523 (2000).
pubmed: 10676955
Duhm, S. et al. Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies. Nat. Mater. 7, 326–332 (2008).
pubmed: 18264103
D’Avino, G. et al. Electrostatic phenomena in organic semiconductors: fundamentals and implications for photovoltaics. J. Phys. Condens. Matter 28, 433002 (2016).
pubmed: 27603960
Yin, Z., Wei, J. & Zheng, Q. Interfacial materials for organic solar cells: recent advances and perspectives. Adv. Sci. 3, 1500362 (2016).
Xu, Z., Tang, B. Z., Wang, Y. & Ma, D. Recent advances in high performance blue organic light-emitting diodes based on fluorescence emitters. J. Mater. Chem. C. 8, 2614–2642 (2020).
Burlingame, Q. et al. Reliability of small molecule organic photovoltaics with electron-filtering compound buffer layers. Adv. Energy Mater. 6, 1601094 (2016).
Lanzani, G. et al. Ultrafast spectroscopy of photoexcitations in α-sexithienyl films: evidence for excitons and polaron-pairs. Synth. Met. 84, 517–520 (1997).
Taliani, C. & Blinov, L. M. The electronic structure of solid α-sexithiophene. Adv. Mater. 8, 353–359 (1996).
Causa’, M. et al. The fate of electron–hole pairs in polymer:fullerene blends for organic photovoltaics. Nat. Commun. 7, 12556 (2016).
pubmed: 27586309
pmcid: 5025766
Devižis, A. et al. Dissociation of charge transfer states and carrier separation in bilayer organic solar cells: a time-resolved electroabsorption spectroscopy study. J. Am. Chem. Soc. 137, 8192–8198 (2015).
pubmed: 26037526
Watanabe, K. et al. Ultrafast decay dynamics of excited and charged states in alpha- sexithienyl film as revealed by femtosecond transient absorption and picosecond fluorescence spectroscopy. J. Phys. Chem. B 101, 1510–1519 (1997).
Klein, G. Transient femtosecond spectroscopy in a-sexithiophene single crystals. Chem. Phys. Lett. 320, 65–69 (2000).
Glowe, J.-F. et al. Charge-transfer excitons in strongly coupled organic semiconductors. Phys. Rev. B 81, 041201 (2010).
Fichou, D., Horowitz, G., Xu, B. & Garnier, F. Stoichiometric control of the successive generation of the radical cation and dication of extended α-conjugated oligothiophenes: a quantitative model for doped polythiophene. Synth. Met. 39, 243–259 (1990).
Wu, J. et al. Exceptionally low charge trapping enables highly efficient organic bulk heterojunction solar cells. Energy Environ. Sci. 6, 11–13 (2020).
Gasparini, N. et al. Polymer: nonfullerene bulk heterojunction solar cells with exceptionally low recombination rates. Adv. Energy Mater. 7, 1701561 (2017).
Heiber, M. C. et al. Measuring the competition between bimolecular charge recombination and charge transport in organic solar cells under operating conditions. Energy Environ. Sci. 11, 3019–3032 (2018).
Lin, Y. L. et al. Enhanced sub-bandgap efficiency of a solid-state organic intermediate band solar cell using triplet–triplet annihilation. Energy Environ. Sci. 10, 1465–1475 (2017).
Lanzani, G., Cerullo, G., Stagira, S., De Silvestri, S. & Garnier, F. Ultrafast spectroscopy of dark states in solid state sexithiophene. J. Chem. Phys. 111, 6474–6480 (1999).
Lane, P. A. et al. Absorption spectroscopy of charged excitations in α-sexithiophene: evidence for charge conjugation symmetry breaking. Chem. Phys. 210, 229–234 (1996).
Köhler, A. et al. Charge separation in localized and delocalized electronic states in polymeric semiconductors. Nature 392, 903–906 (1998).
Moses, D., Dogariu, A. & Heeger, A. J. Ultrafast detection of charged photocarriers in conjugated polymers. Phys. Rev. B - Condens. Matter Mater. Phys. 61, 9373–9379 (2000).
Hendry, E., Schins, J. M., Candeias, L. P., Siebbeles, L. D. A. & Bonn, M. Efficiency of exciton and charge carrier photogeneration in a semiconducting polymer. Phys. Rev. Lett. 92, 1–4 (2004).
Kozlov, O. V. et al. Ultrafast exciton-to-polaron conversion in densely packed small organic semiconducting molecules. Adv. Opt. Mater. 5, 1700024 (2017).
Burkhard, G. F., Hoke, E. T., Beiley, Z. M. & Mcgehee, M. D. Free carrier generation in fullerene acceptors and its effect on polymer photovoltaics. J. Phys. Chem. C. 116, 26674–26678 (2012).
Keiderling, C., Dimitrov, S. & Durrant, J. R. Exciton and charge generation in PC60BM thin films. J. Phys. Chem. C. 121, 14470–14475 (2017).
Hahn, T. et al. Role of intrinsic photogeneration in single layer and bilayer solar cells with C60 and PCBM. J. Phys. Chem. C. 120, 25083–25091 (2016).
He, X. et al. Photogenerated intrinsic free carriers in small-molecule organic semiconductors visualized by ultrafast spectroscopy. Sci. Rep. 5, 1–11 (2015).
Li, Y., Li, P. & Lu, Z.-H. Molecular orientation and energy levels at organic interfaces. Adv. Electron. Mater. 2, 1600306 (2016).
Lorch, C. et al. Templating effects of α-sexithiophene in donor–acceptor organic thin films. J. Phys. Chem. C. 119, 23211–23220 (2015).
Hörmann, U. et al. Voc from a morphology point of view: the influence of molecular orientation on the open circuit voltage of organic planar heterojunction solar cells. J. Phys. Chem. C. 118, 26462–26470 (2014).
Taima, T. et al. Sexithiophene-based photovoltaic cells with high light absorption coefficient via crystalline polymorph control. J. Phys. Chem. C 121, 19699–19704 (2017).
Nakano, K. & Tajima, K. Organic planar heterojunctions: from models for interfaces in bulk heterojunctions to high-performance solar cells. Adv. Mater. 29, 1603269 (2017).
Kouki, F., Spearman, P., Valat, P., Horowitz, G. & Garnier, F. Experimental determination of excitonic levels in α-oligothiophenes. J. Chem. Phys. 113, 385–391 (2000).
Horowitz, G. et al. Growth and characterization of sexithiophene single crystals. Chem. Mater. 7, 1337–1341 (1995).
Matsushima, T., Matsuo, H., Yamamoto, T., Nakao, A. & Murata, H. Horizontally oriented molecular thin films for application in organic solar cells. Sol. Energy Mater. Sol. Cells 123, 81–91 (2014).
Li, J., D’Avino, G., Duchemin, I., Beljonne, D. & Blase, X. Accurate description of charged excitations in molecular solids from embedded many-body perturbation theory. Phys. Rev. B 97, 1–13 (2018).
Schwarze, M. et al. Impact of molecular quadrupole moments on the energy levels at organic heterojunctions. Nat. Commun. 10, 2466 (2019).
pubmed: 31165738
pmcid: 6549189
Opitz, A. et al. Bipolar charge transport in organic field-effect transistors: enabling high mobilities and transport of photo-generated charge carriers by a molecular passivation layer. Org. Electron. 13, 1614–1622 (2012).
Sakanoue, T., Yahiro, M., Adachi, C., Takimiya, K. & Toshimitsu, A. Electrical characteristics of single-component ambipolar organic field-effect transistors and effects of air exposure on them. J. Appl. Phys. 103, 094509 (2008).
Duchemin, I., Guido, C. A., Jacquemin, D. & Blase, X. The Bethe-Salpeter formalism with polarisable continuum embedding: reconciling linear-response and state-specific features. Chem. Sci. 9, 4430–4443 (2018).
pubmed: 29896384
pmcid: 5956976
Liu, J. et al. Fast charge separation in a non-fullerene organic solar cell with a small driving force. Nat. Energy 1, 16089 (2016).
Perdigón-Toro, L. et al. Barrierless free charge generation in the high-performance PM6:Y6 bulk heterojunction non-fullerene solar cell. Adv. Mater. 32, e1906763 (2020).
pubmed: 31975446
Siegrist, T. et al. The crystal structure of the high-temperature polymorph of α-hexathienyl (α-6T/HT). J. Mater. Res. 10, 2170–2173 (1995).
Pizzirusso, A., Savini, M., Muccioli, L. & Zannoni, C. An atomistic simulation of the liquid-crystalline phases of sexithiophene. J. Mater. Chem. 21, 125–133 (2011).
Phillips, J. C. et al. Scalable molecular dynamics with NAMD. J. Comput. Chem. 26, 1781–1802 (2005).
pubmed: 16222654
pmcid: 2486339
D’Avino, G., Muccioli, L., Zannoni, C., Beljonne, D. & Soos, Z. G. Electronic polarization in organic crystals: a comparative study of induced dipoles and intramolecular charge redistribution schemes. J. Chem. Theory Comput. 10, 4959–4971 (2014).
pubmed: 26584380