Device Lifetime

Lifetime simulations can be performed to understand the role of degradation processes on the OLED performance.

Create Materials

Degradation events involve a change in molecular properties of the layer materials. For this reason, we will create both healthy and degraded variants of the dye molecule.

Phosphorescent Dye

Ir(ppy)3 is used as the phosphorescent dye. We will select the corresponding template when creating a new material.

We specify a HOMO level of -5.27 eV and a LUMO level of -1.86 eV. A Gaussian broadening is enabled by default. For the excitons, we use a singlet binding energy of 0.75 eV and a triplet binding energy of 1 eV. The Dexter-type exciton diffusion prefactor is set to 1, with an associated decay length of 0.3 nm.

An intersystem crossing rate of \(10^{10}\,\textrm{s}^{-1}\) is specified. The reverse intersystem crossing rate is set to 0. The radiative decay rate of the triplet excitons is set to \(6.1\cdot{}10^{5}\,\textrm{s}^{-1}\). The non-radiative decay rate is set to \(1.9\cdot{}10^{4}\,\textrm{s}^{-1}\).

Degraded Dye

The deactivated Ir(ppy)3 dye molecule loses access to its radiative decay pathway. We create a new material to store these properties.

We specify a HOMO level of -5.3 eV and a LUMO level of -2.25 eV. The Gaussian broadening is maintained. For the excitons, we use a singlet binding energy of 0.85 eV and a triplet binding energy of 1.25 eV. The Dexter-type exciton diffusion prefactor is set to 1, with an associated decay length of 0.3 nm.

An intersystem crossing rate of \(10^{10}\,\textrm{s}^{-1}\) is specified. The reverse intersystem crossing rate is set to 0. The radiative decay rate of the triplet excitons is set to 0 following deactivation. The non-radiative decay rate is kept at \(1.9\cdot{}10^{4}\,\textrm{s}^{-1}\).

Host

CBP is used as the host material. Select the appropriate template when creating a new material entry.

We use a HOMO level of -6.08 eV and a LUMO level of -1.75 eV. A Gaussian broadening is enabled by default. For the excitons, we use a singlet binding energy of 1 eV and a triplet binding energy of 1.7 eV. For Dexter-type exciton transfer, a prefactor of 0.95 is used along with a decay length of 0.3.

The singlet-triplet generation ratio will be set to 0.25. Thermalization losses during exciton transport from the dye through the host are included by setting the non-radiative decay rates to \(10^{5}\,\textrm{s}^{-1}\) for singlets and \(10^{4}\,\textrm{s}^{-1}\) for triplets. The radiative decay rates are set to 0.

Electron Transport Layer

TPBi is used as an electron transport layer. Select the Transport template when creating a new material.

We use a HOMO level of -6.2 eV and a LUMO level of -1.7 eV. For the excitons, we use a singlet binding energy of 0.75 eV and a triplet binding energy of 1 eV. For Dexter-type exciton transfer, a prefactor of 1 is used along with a decay length of 0.3. A non-radiative decay rate of \(10^{8}\,\textrm{s}^{-1}\) is specified for both excitons.

Hole Transport Layer

TAPC is used as the hole transport layer. We use a HOMO level of -5.5 eV and a LUMO level of -0.96 eV. For the excitons, we use a singlet binding energy of 1 eV and a triplet binding energy of 1.59 eV. For Dexter-type exciton transfer, a prefactor of 1 is used along with a decay length of 0.3. A non-radiative decay rate of \(10^{8}\,\textrm{s}^{-1}\) is specified for both excitons.

Electron Blocking Layer

fac-Ir(pmb)3 is used as an electron blocking layer. Select the Advanced template when creating a new material.

We use a HOMO level of -5.2 eV and a LUMO level of -1 eV. A Gaussian broadening of 0.1 eV is enabled for both polarons. For the excitons, we use a singlet binding energy of 0.8 eV and a triplet binding energy of 1.4 eV. The Gaussian broadening is set to 0.05 for both excitons. For Dexter-type exciton transfer, a prefactor of 0.9 is used along with a decay length of 0.3.

For the triplet excitons, we set a radiative decay rate of \(3.4\cdot{}10^{5}\,\textrm{s}^{-1}\) along with a non-radiative decay rate of \(5.7\cdot{}10^{5}\,\textrm{s}^{-1}\). The singlet decay rates are kept at 0.

Create Compositions

We will create a host-guest system for the emission layer.

  • We use a fraction of 0.9 for the CBP host material

  • We use a fraction of 0.1 for the Ir(ppy)3 dye

  • We add the degraded Ir(ppy)3 material to the composition with a fraction of 0. This makes the material accessible for degradation simulations

Create a Stack

We will create a new stack and add the different layers.

  • Add a 20 nm layer of TAPC

  • Add a 5 nm layer of fac-Ir(pmb)3

  • Add a 40 nm layer of the CBP/Ir(ppy)3 composite

  • Add a 20 nm layer of TPBi

Enable the default Förster interactions to include the relevant excitonic processes.

In the Degradation Processes section of the stack editor, we can specify excitonic events that can trigger degradation of the materials. Selecting the Add Degradation Process option will open the degradation editor.

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Fig. 57 Degradation process overview in the stack editor

We select Degradation upon exciton generation as the cause of the degradation event. We select Ir(ppy)3 as the starting material and degraded Ir(ppy)3 as the product material. We assign a probability of 1.0. All annihilation events occurring in the Ir(ppy)3 phase will then cause the dye to be converted into the degraded material that was specified earlier. Select the Save option to add this mechanism to the stack.

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Fig. 58 Degradation editor settings

Multiple independent processes can be added. For the current stack, we will add a second degradation event for Degradation upon polaron quenching. We will use a probability of 0.8, such that only 80% of polaron quenching reactions will trigger degradation.

Create a Parameter Set

Selecting the Lifetime Simulation template for the parameter set will configure the simulation to include degradation events. The Degradation option will have been enabled in the Modules tab.

We will set the voltage at 6 V. The remaining parameter settings are kept at their default values.

Running the Simulation

We will configure a simulation using a single disorder instance.

Once the simulation has completed, device degradation statistics are found in the OLED Degradation section of the Multibox Report.