Electrothermal feedback in Organic Devices (EFOD)
Final Report Abstract
The project was intended to investigate non-linear self-heating effects in organic devices. A main result is the development of an OLED model that describes the temperature dependent current-voltage characteristics of a temperature stable OLEDs. The model automatically reproduces a current-voltage regime of negative differential resistance, if self-heating is solved self-consistently. The parameterization has been successfully transferred into a simulation tool at the Weierstraß institute. Simulations on large areas then predict the existence of “switched-back” regions that are characterized by a locally declining current density although the total device current increases. We have been able to confirm these regions experimentally. An important parameter of our model is the effective band gap of the OLEDs and we adopted a method typically used for solar cells to measure the temperature dependent open-circuit voltage that is created when an OLED is irradiated with UV light. Another surprising result was the fact that organic solar cells show a turnover of the open-circuit voltage upon increasing illumination intensities that can be described by an effective electrothermal feedback taking place between the quasi-Fermi levels and the illumination intensity. Fitting experimental data leads to the determination of the effective band gap and the thermal resistance of the environment from a single measurement curve at room temperature. The results have a wider relevance as the effect is not related to organic semiconductors but applies to all devices made from any semiconductor that create an open-circuit voltage. In a second part of the project, we investigated Joule self-heating in organic transistors. We find that organic permeable base transistors show a pronounced electrothermal feedback, by proving the existence of selfheating related current-voltage regimes of negative differential resistance. The fact that the charge transport in these devices is enhanced at higher temperatures can be made use of when at higher power dissipations the charge-carrier mobility increases and higher transit frequencies are achieved. In contrast, organic field-effect transistors with high mobility crystalline organic semiconductors show almost no activation of the transconductance. Then, there is no electrothermal feedback that results in catastrophic failure due to thermal runaway. But at the same time, Joule self-heating is not detectable based on currentvoltage curves if these transistors heat up. In general, the project “EFOD” benefitted a lot from considering various device concepts, helping to find similarities and differences, what finally allowed us to achieve new and unexpected insights.
Publications
- (2019) Emissive and charge-generating donor-acceptor interfaces for organic optoelectronics with low voltage losses. Nature materials 18 (5) 459–464
Ullbrich, Sascha; Benduhn, Johannes; Jia, Xiangkun; Nikolis, Vasileios C.; Tvingstedt, Kristofer; Piersimoni, Fortunato; Roland, Steffen; Liu, Yuan; Wu, Jinhan; Fischer, Axel; Neher, Dieter; Reineke, Sebastian; Spoltore, Donato; Vandewal, Koen
(See online at https://doi.org/10.1038/s41563-019-0324-5) - 3D electrothermal simulations of organic LEDs showing negative differential resistance. Optical and Quantum Electronics 49 (10), 330, 2017
M. Liero, J. Fuhrmann, A. Glitzky, T. Koprucki, A. Fischer, S. Reineke
(See online at https://doi.org/10.1007/s11082-017-1167-4) - Nonlinear Contact Effects in Staggered Thin-Film Transistors. Physical Review Applied 8 (5), 054012, 2017
A. Fischer, H. Zündorf, F. Kaschura, J. Widmer, K. Leo, U. Kraft, H. Klauk
(See online at https://doi.org/10.1103/PhysRevApplied.8.054012) - Novel organic light-emitting diode design for future lasing applications. Organic Electronics 48, 132-137, 2017
I. Slowik, A. Fischer, H. Fröb, S. Lenk, S. Reineke, K. Leo
(See online at https://doi.org/10.1016/j.orgel.2017.05.048) - A Pulse-Biasing Small-Signal Measurement Technique Enabling 40 MHz Operation of Vertical Organic Transistors. Scientific Reports 8 (1), 7643, 2018
B. Kheradmand-Boroujeni, M.P. Klinger, A. Fischer, H. Kleemann, K. Leo, F. Ellinger
(See online at https://doi.org/10.1038/s41598-018-26008-0) - Electrothermal Feedback and Absorption-Induced Open-Circuit-Voltage Turnover in Solar Cells. Physical Review Applied 9 (5), 051003, 2018
S. Ullbrich, A. Fischer, Z. Tang, J. Ávila, H.J. Bolink, S. Reineke, K. Vandewal
(See online at https://doi.org/10.1103/PhysRevApplied.9.051003) - Exploiting lateral current flow due to doped layers in semiconductor devices having crossbar electrodes. Organic Electronics 65, 82-90, 2018
Y. Zheng, A. Fischer, N. Sergeeva, S. Reineke, S. Mannsfeld
(See online at https://doi.org/10.1016/j.orgel.2018.10.040) - Full Electrothermal OLED Model Including Nonlinear Self-heating Effects. Physical Review Applied 10 (1), 014023, 2018
A. Fischer, M. Pfalz, K. Vandewal, S. Lenk, M. Liero, A. Glitzky, S. Reineke
(See online at https://doi.org/10.1103/PhysRevApplied.10.014023) - Non-Linear Self-Heating in Organic Transistors Reaching High Power Densities. Scientific reports 8 (1), 9806, 2018
M.P. Klinger, A. Fischer, H. Kleemann, K. Leo
(See online at https://doi.org/10.1038/s41598-018-27689-3) - Investigating Free Charge-Carrier Recombination in Organic LEDs using Open-Circuit Conditions. Advanced Optical Materials 1801426, 2019
J. Wu, A. Fischer, S. Reineke
(See online at https://doi.org/10.1002/adom.201801426)
