Intermolecular charge-transfer states at the interface between electron donating (D) and accepting (A) materials are crucial for the operation of organic solar cells but can also be exploited for organic light-emitting diodes1,2. Non-radiative charge-transfer state decay is dominant in state-of-the-art D–A-based organic solar cells and is responsible for large voltage losses and relatively low power-conversion efficiencies as well as electroluminescence external quantum yields in the 0.01–0.0001% range3,4. In contrast, the electroluminescence external quantum yield reaches up to 16% in D–A-based organic light-emitting diodes5,6,7. Here, we show that proper control of charge-transfer state properties allows simultaneous occurrence of a high photovoltaic and emission quantum yield within a single, visible-light-emitting D–A system. This leads to ultralow-emission turn-on voltages as well as significantly reduced voltage losses upon solar illumination. These results unify the description of the electro-optical properties of charge-transfer states in organic optoelectronic devices and foster the use of organic D–A blends in energy conversion applications involving visible and ultraviolet photons8,9,10,11.
Access optionsAccess options
Subscribe to Journal
Get full journal access for 1 year
only $16.58 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.
Yan, C. et al. Non-fullerene acceptors for organic solar cells. Nat. Rev. Mater. 3, 18003 (2018).
Sarma, M. & Wong, K.-T. Exciplex: an intermolecular charge-transfer approach for TADF. ACS Appl. Mater. Interfaces 10, 19279–19304 (2018).
Benduhn, J. et al. Intrinsic non-radiative voltage losses in fullerene-based organic solar cells. Nat. Energy 2, 17053 (2017).
Qian, D. et al. Design rules for minimizing voltage losses in high-efficiency organic solar cells. Nat. Mater. 17, 703–709 (2018).
Goushi, K., Yoshida, K., Sato, K. & Adachi, C. Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion. Nat. Photon. 6, 253–258 (2012).
Chen, D. et al. Fluorescent organic planar pn heterojunction light-emitting diodes with simplified structure, extremely low driving voltage, and high efficiency. Adv. Mater. 28, 239–244 (2016).
Lin, T.-C. et al. Probe exciplex structure of highly efficient thermally activated delayed fluorescence organic light emitting diodes. Nat. Commun. 9, 3111 (2018).
Davy, N. C. et al. Pairing of near-ultraviolet solar cells with electrochromic windows for smart management of the solar spectrum. Nat. Energy 2, 17104 (2017).
Lungenschmied, C. et al. Flexible, long-lived, large-area, organic solar cells. Sol. Energy Mater. Sol. Cells 91, 379–384 (2007).
Meerheim, R., Körner, C. & Leo, K. Highly efficient organic multi-junction solar cells with a thiophene based donor material. Appl. Phys. Lett. 105, 063306 (2014).
Meng, L. et al. Organic and solution-processed tandem solar cells with 17.3% efficiency. Science 6407, 1094–1098 (2018).
Vandewal, K. Interfacial charge transfer states in condensed phase systems. Annu. Rev. Phys. Chem. 67, 113–133 (2016).
Liu, X. K. et al. Prediction and design of efficient exciplex emitters for high-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes. Adv. Mater. 27, 2378–2383 (2015).
Chang, W. et al. Spin-dependent charge transfer state design rules in organic photovoltaics. Nat. Commun. 6, 6415 (2015).
Attar, Aa. H. A. & Monkman, A. P. Electric field induce blue shift and intensity enhancement in 2D exciplex organic light emitting diodes; controlling electron–hole separation. Adv. Mater. 28, 8014–8020 (2016).
Jenekhe, S. A. & Osaheni, J. A. Excimers and exciplexes of conjugated polymers. Science 265, 765–768 (1994).
Vandewal, K. et al. Efficient charge generation by relaxed charge-transfer states at organic interfaces. Nat. Mater. 13, 63–68 (2014).
Park, S. H. et al. Bulk heterojunction solar cells with internal quantum efficiency approaching 100%. Nat. Photon. 3, 297–303 (2009).
Vandewal, K., Tvingstedt, K., Gadisa, A., Inganäs, O. & Manca, J. V. Relating the open-circuit voltage to interface molecular properties of donor:acceptor bulk heterojunction solar cells. Phys. Rev. B 81, 125204 (2010).
Tvingstedt, K. et al. Radiative efficiency of lead iodide based perovskite solar cells. Nat. Sci. Rep. 4, 6071 (2014).
Rau, U. Reciprocity relation between photovoltaic quantum efficiency and electroluminescent emission of solar cells. Phys. Rev. B 76, 085303 (2007).
McNaught, A. D. & Wilkinson, A. IUPAC Compendium of Chemical Terminology 2nd edn (Blackwell Scientific, 1997).
Tvingstedt, K. & Deibel, C. Temperature dependence of ideality factors in organic solar cells and the relation to radiative efficiency. Adv. Energy Mater. 6, 1502230 (2016).
Banerjee, S. & Anderson, W. A. Temperature dependence of shunt resistance in photovoltaic devices. Appl. Phys. Lett. 49, 38–40 (1986).
Santos, Da. P. L., Dias, F. B. & Monkman, A. P. Investigation of the mechanisms giving rise to TADF in exciplex states. J. Phys. Chem. C 120, 18259–18267 (2016).
Yokoyama, D., Sasabe, H., Furukawa, Y., Adachi, C. & Kido, J. Molecular stacking induced by intermolecular C–HN hydrogen bonds leading to high carrier mobility in vacuum-deposited organic films. Adv. Funct. Mater. 21, 1375–1382 (2011).
Liu, J. et al. Fast charge separation in a non-fullerene organic solar cell with a small driving force. Nat. Energy 1, 16089 (2016).
Liu, X. et al. Efficient organic solar cells with extremely high open-circuit voltages and low voltage losses by suppressing nonradiative recombination losses. Adv. Energy Mater. 9, 1801699 (2018).
Englman, R. & Jortner, J. The energy gap law for radiationless transitions in large molecules. Mol. Phys. 18, 145–164 (1970).
Azzouzi, M. et al. Nonradiative energy losses in bulk-heterojunction organic photovoltaics. Phys. Rev. X 8, 31055 (2018).
Kayes, B. M. et al. 27.6% conversion efficiency, a new record for single-junction solar cells under 1 sun illumination. In IEEE Photovoltaic Specialists Conference (IEEE, 2011).
Zhang, J. et al. Efficient non-fullerene organic solar cells employing sequentially deposited donor–acceptor layers. J. Mater. Chem. A 6, 18225–18233 (2018).
Yang, D. et al. A minimal non-radiative recombination loss for efficient non-fullerene all-small-molecule organic solar cells with a low energy loss of 0.54 eV and high open-circuit voltage of 1.15 V. J. Mater. Chem. A 6, 13918–13924 (2018).
Tang, Z. et al. A new fullerene-free bulk-heterojunction system for efficient high-voltage and high-fill factor solution-processed organic photovoltaics. Adv. Mater. 27, 1900–1907 (2015).
Nikolis, V. C. et al. Reducing voltage losses in cascade organic solar cells while maintaining high external quantum efficiencies. Adv. Energy Mater. 7, 1700855 (2017).
Zhao, W. et al. Fullerene-free polymer solar cells with over 11% efficiency. Adv. Mater. 28, 4734–4739 (2016).
Benduhn, J. et al. Impact of triplet excited states on the open-circuit voltage of organic solar cells. Adv. Energy Mater. 8, 1800451 (2018).
This work was supported by the German Federal Ministry for Education and Research (BMBF) through the InnoProfile project ‘Organische p–i–n Bauelemente 2.2’ (03IPT602X) and by the German Research Foundation (DFG) project Photogen (VA 1035/5-1). X.J. and Y.L. acknowledge support from the China Scholarship Council (nos. 201706140127 and 201506920047, respectively). The authors also acknowledge the DFG for supporting K.T. (project 382633022 ‘RECOLPER’), F.P., S.Ro. and D.N. (SFB 951 ‘HIOS’) and A.F. (RE 3198/6-1 ‘EFOD’).
The authors declare no competing interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Advanced Theory and Simulations (2019)
Locking excitons in two-dimensional emitting layers for efficient monochrome and white organic light-emitting diodes
Journal of Materials Chemistry C (2019)
Nature Materials (2019)
Nature Communications (2019)