(Invited) Automated Multiscale Design Flow for Organic LED Design
Authors: Kaiser Simon , Symalla Franz , Neumann Tobias , Plews Andrew , Vander Velpen Dieter , Vandeplas Erwin , Ke Tung-Huei , Nejim Ahmed 
Published: July 2021

Material scientists can synthesize many organic semiconductors and dopants. While this presents a unique opportunity to device designers, discovering carrier transport parameters becomes a challenge for simulators. To overcome this, a seamless flow that links quantum chemistry calculations to TCAD driven from a single front end GUI is presented here. The developed multiscale simulation workflow links the microscopic to device scale, thereby connecting fundamental chemistry with device design in a parameter-free simulation of a 5-layer red oLED stack with an α-NPD:Ir(MDQ)2(acac) emission layer.
In materials development, quantum chemistry approaches are applied to compute fundamental molecular properties such as orbital energies (HOMO/LUMO) or excitation spectra. Continuum models such as drift diffusion on the other hand are efficient tools for device designers to simulate characteristics such I-V or quantum efficiency of multilayer OLED stacks, based on parametric models.
There are shortcomings that hinder the full exploitation of virtual design for organic electronics. Quantum chemistry methods used to compute properties of single molecules in vacuum neglects the interaction between molecules in organic thin films. Examples include material specific shifts in transport levels (ionization potential, IP, and electron affinity, EA) due to polarization effects, or energy disorder. Mesoscopic material properties such as charge carrier mobility or accurate transport levels (IP/EA) cannot be computed with these methods. These material-specific quantities, however, are essential input parameters for drift diffusion models. Device level simulations of multilayer OLEDs therefore rely on time-consuming and costly measurements.
Consequently, the translation of microscopic properties to the device level is not possible. Further, established methods do not allow developers to analyse chemical structure impact on device performance.
Digital twins of organic layers, constructed by mimicking physical vapour deposition, the properties of molecules embedded in thin films are calculated by taking into account environmental effects on a full quantum-mechanical level.1–5 Besides ab-initio access to transport energies, these molecular quantities are used to compute rates for all microscopic processes that determine device performance, including charge hops between molecules, exciton formation or quenching events. Based on these rates, kinetic Monte-Carlo (KMC) simulations are used to compute material-specific macroscopic properties such as charge carrier mobilities, which are automatically fed to drift diffusion models.6–9
Drift diffusion calculations were performed using Silvaco Atlas.10,11 Quantum mechanical and KMC calculations provided the affinity, LUMO and HOMO values, material disorder and carrier mobility for the OLED stack.
This seamless workflow allows full virtual design that features:

Linking fundamental chemistry to device design for accurate design rules.

Insight into particle distributions and processes that cannot be measured experimentally.

Discovery of the best material and device performance within the design space.

No parametrization of drift diffusion models via experiment is required. All inputs computed from first principles.

Steering the development of physics based SPICE compact models.

Funding was received from the European Union Horizon 2020 research and innovation programme. Grant agreement No. 646176 (EXTMOS)

Neumann, T., Danilov, D., Lennartz, C. & Wenzel, W. Modeling disordered morphologies in organic semiconductors. Journal of Computational Chemistry vol. 34 2716–2725 (2013).

Friederich, P., Rodin, V., von Wrochem, F. & Wenzel, W. Built-In Potentials Induced by Molecular Order in Amorphous Organic Thin Films. ACS Appl. Mater. Interfaces
10, 1881–1887 (2018).

Friederich, P., Symalla, F., Meded, V., Neumann, T. & Wenzel, W. Ab Initio Treatment of Disorder Effects in Amorphous Organic Materials: Toward Parameter Free Materials Simulation. Journal of Chemical Theory and Computation vol. 10 3720–3725 (2014).

Friederich, P., Meded, V., Symalla, F., Elstner, M. & Wenzel, W. QM/QM Approach to Model Energy Disorder in Amorphous Organic Semiconductors. Journal of Chemical Theory and Computation vol. 11 560–567 (2015).

Friederich, P. et al. Molecular Origin of the Charge Carrier Mobility in Small Molecule Organic Semiconductors. Advanced Functional Materials vol. 26 5757–5763 (2016).

Symalla, F. et al. Multiscale Simulation of Photoluminescence Quenching in Phosphorescent OLED Materials. Advanced Theory and Simulations vol. 3 1900222 (2020).

Symalla, F. et al. 19‐4: Boosting OLED Performance with Ab‐initio Modeling of Roll‐off and Quenching Processes. SID Symposium Digest of Technical Papers vol. 50 259–262 (2019).

Symalla, F. et al. 26-4: Computer-Aided Optimization of Multilayer OLED Devices. SID Symposium Digest of Technical Papers vol. 49 340–342 (2018).

Symalla, F. et al. Charge Transport by Superexchange in Molecular Host-Guest Systems. Phys. Rev. Lett.
117, 276803 (2016).

Introduction to Silvaco© ATLAS TCAD Software. Modeling and Electrothermal Simulation of SiC Power Devices 19–50 (2019) doi:10.1142/9789813237834_0003.

SILVACO, ATLAS User’s Manual-DEVICE SIMULATION SOFTWARE, USA, Santa Clara, 2020

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