Photoluminescence¶
Absorption processes can be included to replicate photoresponse measurements. Device models can be constructed to simulate photovoltaics and photodetectors.
Create Materials¶
In this tutorial, we will model the photoluminescent behavior of an organic photovoltaic (OPV).
Donor¶
P3HT is used as the donor material. Excitation processes are assumed to be singlet-dominant. We therefore choose to use the Fluorescent Dye template.
We set a HOMO level of -5.2 eV and a LUMO level of -3.3 eV. For the excitons, we use a singlet binding energy of 1.2 eV and a triplet binding energy of 1.4 eV. Default Gaussian broadening is used for both polaron and exciton energy levels. The Dexter prefactor for excitonic transfer is set to 1.9.
The fluorescent material template will have automatically configured a radiative singlet decay process. We will set this rate to \(10^{7}\,\textrm{s}^{-1}\). We will simulate a singlet-mediated device by setting both singlet fractions to 1. ISC rates remain at zero.
Acceptor¶
PCBM is used as the acceptor material. We will use the Fluorescent Dye template to describe the singlet-dominant system.
We set a HOMO level of -6.1 eV and a LUMO level of -3.9 eV. For the excitons, we use a singlet binding energy of 1.6 eV and a triplet binding energy of 1.9 eV. Default Gaussian broadening is used for both polaron and exciton energy levels.
The Dexter prefactor for excitonic transfer is set to 3.1. The singlet radiative decay rate is set to \(10^{7}\,\textrm{s}^{-1}\). Both singlet fractions are set to 1.
Electron Transport Layer¶
BCP will be used as the electron transport layer. We select the Transport template to create a new material.
We set a HOMO level of -6.3 eV and a LUMO level of -2.9 eV. A Gaussian energy level broadening is enabled by default. For the excitons, we use a singlet binding energy of 1.5 eV and a triplet binding energy of 2.6 eV.
Hole Transport Layer¶
PEDOT:PSS will be used as the hole transport layer.
We set a HOMO level of -5 eV and a LUMO level of -2.3 eV. A Gaussian energy level broadening is enabled by default. For the excitons, we use a singlet binding energy of 0.7 eV and a triplet binding energy of 1.2 eV.
Create a Stack¶
We will utilize pure compositions to construct the OPV stack. We start with a 5 nm BCP electron transport layer. We then add 10 nm layers for both the P3HT donor and PCBM acceptor. A 5 nm PEDOT:PSS hole transport layer is added to complete the device.
Enable the default Förster processes to include inter-layer singlet diffusion.
Fig. 59 Absorption configurations in the stack editor¶
Photo-absorption processes can be added in the stack editor. Select the Add Absorption option to define a new absorption process. We select the P3HT material in the donor layer. Absorption is described as a fixed excitation probability per incident photon. We will assume a factor of 0.8, accounting for optical loss processes. Use the Save button to commit this process to the stack. Then repeat these steps to add the same reaction to the PCBM material in the acceptor layer.
Fig. 60 Absorption process editor¶
Create a Parameter Set¶
Bumblebee offers two parameter templates for photoluminescent processes.
The Photoluminescence template configures a periodic box for measuring the bulk properties of the layer materials. In addition to configuring photoluminescent simulation, higher resolutions are obtained compared to the default Periodic Box
The PV/Photodetector template is used for regular device simulations
We will use the PV template to model the photovoltaic device.
Device Settings¶
We will set the electrode levels to -4.6 for a silver anode and -4.7 for an ITO cathode contact. The external device voltage will be set to 0.5 V.
Having chosen a PV template, the photoluminescence module should have been enabled automatically in the Modules tab.
Fluence¶
Photo-absorption settings are configured in the Photoluminescence tab.
Fig. 61 Photoluminescence settings in the parameter set editor¶
The incident irradiation is set by defining a device fluence. We use a value of 300 \(\textrm{photons/s/nm}^3\), in line with ambient solar lighting conditions.
We define absorption processes to yield a singlet exciton inside the OPV device.
When simulating bulk material properties, a minimum exciton density can also be added in this tab. For the current device simulation, we will keep this value at 0.
Starting the Simulation¶
For this tutorial, we will set up a new simulation using a single disorder instance.
A fluence sweep can be performed to investigate how the device current changes as a function of the irradiation. We choose to vary the fluence from 300 to 1500 \(\textrm{photons/s/nm}^3\) in 5 steps.
If you wish to limit the computational time required for this tutorial, you can perform a single-point calculation instead. This will use the 300 \(\textrm{photons/s/nm}^3\) default fluence defined in the parameter set.
Simulation Output¶
The power efficiency of the OPV can be viewed in the OLED Luminance section of the Sweep Report.
Absorption characteristics can be viewed in the Transient Photoluminescence section of the Multibox Report for various irradiation densities.