Celebrating 20 Years of Setfos

/

This year, Fluxim celebrates two decades of Setfos, our advanced simulation software that has been pivotal in enabling OLED and solar cell development. In this special newsletter edition, we revisit influential publications and milestones, reflecting on how Setfos has driven advancements and fostered collaboration worldwide. 

Setfos at the Forefront of Research 

Setfos has been an essential tool for researchers in academia and industry, advancing OLEDs, perovskite solar cells, photodetectors, batteries and more. It supports researchers in modeling and analyzing optoelectronic processes, from early concept validation to device optimization, enhancing the performance of optoelectronic devices. With hundreds of studies utilizing Setfos, it has contributed to major advancements in the field. 

Here are some key publications that illustrate the impact Setfos has had on research and how it has developed over the years. 

The First (S)Etfos Paper  

Setfos was not always known by its current name. The first version, called Etfos, first appeared in a publication detailing its application in modeling the optical performance of OLEDs. Beat Ruhstaller, the first author and who would become the founder of Fluxim AG, spearheaded the development of this software, which Fluxim continues to sell and develop under its current name, SETFOS. 

This first (S)etfos paper [1] by our now CEO Beat Ruhstaller emphasized the need for a dedicated OLED simulation tool to optimize devices and materials. The team developed a comprehensive model that considered both electronic and optical processes in an OLED.  The electronic model was based on drift-diffusion combined with exciton diffusion and decay. The optical part of the model considers the emission to originate from embedded radiative dipoles. 

This first version of the code, called ETFOS, was validated with several experiments on different OLEDs. To assess the accuracy of the model, the team collected current-voltage characteristics and angular electroluminescence spectra, and analyzed how OLED performance scaled with variations in layer thickness. They also compared the photoluminescence of the materials in the stack with simulated results, specifically to validate the effects of exciton quenching near metal interfaces. The general conclusion from this preliminary report was that the optical portion of their model was robust and generated reliable predictions. At the time, further research was necessary to refine the electronic aspects of the model, using data from multi-layered structures.  

The First Paper Published by a Customer  

In the early 2000’s the emergence of OLED technology meant we soon received a lot of interest in our newly developed simulation software.  

This 2006 paper by Kiy et al.[2] presents a high-throughput apparatus (HTA-7) for fabricating and testing polymer light-emitting diodes (PLEDs). The researchers fabricated PLEDs by spin-coating different polymers onto 49 substrates and varying the concentration of the phosphorescent emitter within the host polymeric blend, while keeping other parameters constant. To confirm that the emitter concentration was the only variable affecting the PLED performance, they utilized Etfos to analyze the emission spectra and ensure consistent polymer layer thickness across the devices. Figure 7 from the paper (included in the image above) showcases the electroluminescence spectra obtained from 44 different PLEDs. The researchers explain that while the internal emission spectrum of the emitter is independent of the layer thickness, the externally measured spectrum is influenced by internal reflections within the device, which are sensitive to thickness variations. By comparing the experimental spectra with simulations by Etfos, they could assess the thickness uniformity.  This analysis allowed them to conclude that the thickness variations across the 44 working devices were less than 5 nm, validating their experimental approach. 

2007: Etfos becomes S-etfos 

In 2007 at SID, Beat presented the invited paper: Optoelectronic OLED Modeling for Device Optimization and Analysis [3].  

With this work, he presented an extension of ETFOS.  The optical model in ETFOS (Emissive Thin Film Optics Simulator), was used mainly to simulate light emission from oscillating dipoles within the OLED layers. S-ETFOS (Semi-conducting Emissive Thin Film Optics Simulator) had in addition an extensive drift-diffusion module, allowing for combined electro-optical simulations. This proved valuable in capturing charge density profiles and other complex aspects of the OLED functioning mechanisms. Validation against experimental data from several polymer LEDs (PLEDs) confirmed the model’s accuracy. Notably, the team demonstrated that the emission zone was located near the interface of the emissive polymer layer and PEDOT, showing a higher recombination rate at that junction. By fitting simulations to electroluminescence data, the team identified that emissions largely originated from the anode side of the emissive layer.

Ultimately, this paper underscored the power of combining optical and electronic simulations, showing how the newly developed S-ETFOS serves as a crucial tool for optimizing OLEDs. 

The First Papers Published on Solar Cells 

At Fluxim, we are committed to advancing research tools to stay at the forefront of innovation. It wasn’t long before we expanded Setfos beyond OLEDs to help researchers working on solar cells as well. This new application was first shown in the paper by former colleague R. Häusermann et al. [4] "Coupled Optoelectronic Simulation of Organic Bulk-Heterojunction Solar Cells: Parameter Extraction and Sensitivity Analysis" in 2009. The team shows how to use Setfos to perform a coupled optoelectronic simulation of an organic bulk-heterojunction (BHJ) solar cell. The optical simulation used a transfer matrix formalism to compute the electromagnetic field and the absorption profile, which was fed into the electrical simulation. This electrical model incorporates drift-diffusion equations, Langevin recombination, and charge-transfer (CT) exciton dynamics based on the Onsager-Braun model. Through parameter extraction and sensitivity analysis, Setfos demonstrated its expanded capabilities in accurately capturing key characteristics of BHJ solar cells. The study also highlighted areas for improvement, particularly in representing the electric field's influence on CT-exciton dissociation, paving the way for further refinements in solar cell modeling.

Setfos & Perovskite Solar Cells 

As perovskite solar cell research was advancing rapidly, understanding the behavior of these devices under various operative conditions was becoming an essential task. In a study lead by our former colleague Dr. Martin Neukom [5], we demonstrated how Setfos, which treated both ionic and electronic charge transport, could be used to describe experimental preconditioned IV-curves of a perovskite PV. Our findings revealed that hysteresis in the IV-curves is closely tied to charge carrier diffusion length and surface recombination at the contacts. High surface recombination leads to pronounced hysteresis, as charges are driven to the opposite contact and recombine when ions are preconditioned at 0V, neutralizing the built-in field. In contrast, solar cells with longer diffusion lengths and lower surface recombination show high efficiency and minimal hysteresis, supported by a charge density gradient that aids diffusion-driven charge extraction even against the electric field. This study emphasized the importance of increasing diffusion length and reducing surface recombination to improve stability in perovskite solar cells. Additionally, it highlighted the influence of contact materials and device architecture on surface recombination, shedding light on the variability in hysteresis across different perovskite PV designs. 

Most Cited Papers Enabled with Setfos 

Citations serve as a vital measure of a paper's impact and value within the research community. After diving into 20 years of publications, we have identified the most cited works in PV and LED research where Setfos has been used. These influential papers highlight Setfos' versatility in simulating complex optoelectronic processes and underscore its significant contribution to several advancements in these research fields. 

LEDS

“Highly efficient blue thermally activated delayed fluorescence emitters based on symmetrical and rigid oxygen-bridged boron acceptors” 

CITATIONS: 635

Fig. 1. Molecular orientation analysis. a, Measured and simulated effective decay rate and dipole orientation of TDBA–DI in DBFPO host. b, The calculated maximum EQE according to the molecular orientation factor and PLQY. 

This Nature Photonics paper [6] reports the development of two highly efficient deep-blue thermally activated delayed fluorescence (TADF) emitters, TDBA-AC and TDBA-DI, designed to achieve high photoluminescence quantum yield and narrow-band blue emission. To understand and verify the efficiency, the researchers used Setfos 4.3 for optical simulations, inputting parameters such as refractive index, extinction coefficient, dipole orientation factor, layer thickness, and emission spectra. Setfos predicted a maximum external quantum efficiency (EQE) of 39.3%, closely matching the experimentally measured EQE of 38.15 ± 0.42%, confirming that the high efficiency stemmed from the horizontal orientation of TDBA-DI. This research underscores the potential of precise dipole alignment in developing high-performance electroluminescent materials, setting a foundation for future emitter design. 

Photovoltaics 

“Perovskite-Organic Tandem Solar Cells with Indium Oxide Interconnect”

CITATIONS: 267

Fig. 2. Semi-empirical model of the tandem cell efficiency vs. energy-gap of the organic and perovskite sub-cells. 

This paper from Brinkman et al. [7], published in Nature in 2022, describes the fabrication and characterization of a perovskite-organic tandem solar cell with a record-breaking efficiency of 24.0% (certified 23.1%). The researchers used a combination of a wide-gap perovskite sub-cell and a narrow-gap organic sub-cell connected by an ultrathin indium oxide (InOx) layer. 

A key challenge for the team was to achieve a high open-circuit voltage (Voc) in a wide-gap perovskite cell while maintaining a high fill factor. The researchers overcame this by optimizing charge extraction layers and passivating the perovskite surface. They also developed a novel, low-loss interconnect based on a 1.5 nm InOx layer deposited by atomic layer deposition (ALD). This interconnect facilitated efficient recombination of charges between the sub-cells without significant optical or electrical losses. 

The researchers used Setfos to identify a suitable wide-gap perovskite material for the tandem cell. The simulations predicted an efficiency of 25.5% with a perovskite bandgap in the range of 1.85–1.92 eV, assuming a tandem fill factor of 80% and a voltage loss of 0.5 V in each sub-cell. This simulation helped the researchers to select FA0.8Cs0.2Pb(I0.5Br0.5)3 as a suitable perovskite composition with a bandgap of 1.85 eV. 

The Latest Paper with Setfos 

And the flow of papers does not stop. The latest research in which Setfos is used investigates the role of OLED architecture in controlling polaron accumulation caused by spontaneous orientation polarization (SOP). By using SOP-active host materials in the emissive layer, Pakhomenko et al. [8] were able to shift polaron accumulation towards the HTL/EML interface, reducing exciton-polaron quenching and boosting peak internal quantum efficiency. 

Setfos helped them calculate the device’s light outcoupling efficiency, factoring in parameters such as the isotropic dipole orientation and the optical constants of the materials, which influence light propagation and brightness. This research demonstrates the importance of device design in enhancing OLED performance through precise control of SOP effects. 

Most Unusual Use of Setfos 

Xenon Flash Lamp Lift-Off Technology without Laser for Flexible Electronics 

We have developed Setfos to support researchers working on a wide variety of semi-conducting devices, mainly LEDs, PVs and photodetectors. New functionality and modules are often developed based on customer requests and they are mainly from researchers working in these fields. This doesn’t mean that we are not pleased to see “unusual” uses of Setfos from time to time. This work published in 2020 by Lee et al. [9] investigated a novel lift-off technology for flexible electronics using a xenon flash lamp (XFL) instead of a laser. The process involves using a light to heat conversion layer (LTHC), which separates a polyimide film from a carrier substrate. The researchers used Setfos software to simulate and optimize the optical properties of the LTHC, consisting of multiple thin film layers, including molybdenum (Mo) and silicon dioxide (SiO2)4. They determined the ideal thickness of each layer for maximum light absorption. The study demonstrated that XF-LO technology can effectively lift off PI films of varying thicknesses without damage, offering a potential alternative to the more expensive laser-based methods. 

Over 550 Research Papers Have Used Setfos 

These publications show how Setfos has been instrumental in advancing research across various research fields. Beyond the studies highlighted here, Setfos has supported over 550 publications on OLEDs, perovskites PVs, OPVs, photodetectors, batteries and more. 

We wish to thank all our research colleagues who have used Setfos for the last 20 years and helped maintain its position as the leading simulation software for OLEDs and PVs. We also wish to thank all the “Fluximers”, past and present who have contributed to the development and success of Setfos.

For more Setfos insights and access to these papers, visit the webpage: www.fluxim.com/setfos. 

Are you inspired to use Setfos for your research? Reach out to Fluxim to discover how we can support and enhance your projects. 

References

[1] Parameter Extraction and Validation of an Electronic and Optical Model for Organic Light-emitting Devices, Ruhstaller, B., et al., Simulation of Semiconductor Processes and Devices (pp. 2-4). ISBN 3-211-22468-8.1 (2004)

[2] Systematic studies of polymer LEDs based on a combinatorial approach, Kiy, M., Kern, R., Beierlein, T. A., & Winnewisser, C. J., Organic Light Emitting Materials and Devices X, (6333, 633307). SPIE, (2006) https://doi.org/10.1117/12.680606 

[3] Optoelectronic OLED Modeling for Device Optimization and Analysis.  Ruhstaller, B., et al. SID Symposium Digest of Technical Papers, 38: 1686-1690 (2007). https://doi.org/10.1889/1.2785649 

[4] Coupled optoelectronic simulation of organic bulk-heterojunction solar cells: Parameter extraction and sensitivity analysis, R. Häusermann, et al. J. Appl. Phys. 106, 104507, (2009). https://doi.org/10.1063/1.3259367

[5] Why perovskite solar cells with high efficiency show small IV-curve hysteresis, Neukom, M. T., et al. Solar Energy Materials and Solar Cells, 169, 159–166, (2017).  https://doi.org/10.1016/j.solmat.2017.05.021 

[6] Highly efficient blue thermally activated delayed fluorescence emitters based on symmetrical and rigid oxygen-bridged boron acceptors Ahn, D. H., et al (2019).  Nature Photonics, 13, 306, (2019). https://doi.org/10.1038/s41566-019-0415-5   

[7] Perovskite-Organic Tandem Solar Cells with Indium Oxide Interconnect, Brinkmann, K. O. et al.  Nature 604, 280 (2022). https://doi.org/10.1038/s41586-022-04455-0 

[8] Controlling Polarization-Induced Polaron Accumulation in OLEDs via Device Design, E. Pakhomenko, et al. Adv. Funct. Mater., 2412329, (2024). https://doi.org/10.1002/adfm.202412329 

[9] Xenon Flash Lamp Lift-Off Technology without Laser for Flexible Electronics, Lee, S.I.; Jang, S.H.; Han, Y.J.; Lee, J.y.; Choi, J.; Cho, K.H. . Micromachines , 11, 953. (2020) https://doi.org/10.3390/mi11110953