Transient Simulation of MEH-PPV Polymer LED

organicex02.in : Transient Simulation of MEH-PPV Polymer LED

Requires: Blaze/Organic Display
Minimum Versions: Atlas 5.22.1.R

This example demonstrates the transient simulation of an Organic Light Emitting Diode (OLED). It demonstrates:

  • OLED structure definition using Atlas syntax
  • Material parameter specification
  • Choosing the OLED physical models
  • The Langevin and Exciton Density contour plot at 12V
  • Transient response of the Exciton Density and Anode Current

The simulation structure used in this example is the same as the previous example. After specifying the simulation structure, a steady-state simulation is performed to initialize the transient analysis. DT.MAX on the METHOD statement specifies the maximum time-step for transient simulation.

The PROBE statement is used to save the singlet exciton density at the centre of the OLED structure. The value of this parameter is saved to the log file. The OUTPUT statement is used to specify the Langevin recombination rate to be saved in the structure file.

In this example, a 12V square voltage pulse of 0.5us is used to study the transient response of the OLED. To perform this simulation, a log file is first opened to save all the simulated data after the LOG statement. Next, the SOLVE statement sets the anode at 0V for 50ns. This is followed by ramping the anode from 0V to 12V with a ramp time of 5ns. The parameter DT in the second SOLVE statement is used to set the first time step of the transient. All other time steps are calculated automatically by the program. A DT value of ramptime/100 is a safe one under most circumstances. The TSTOP parameter will set the time until which the simulation will continue. Once the simulation reaches 500ns, the third SOLVE statement will ramp down the anode voltage from 12V to 0V with a ramp time of 5ns. The anode voltage remains at 0V till 550ns.

In this example, 4 plots are automatically generated by the TONYPLOT statements after the simulation. The first and second plots show the Langevin Recombination and singlet exciton density contour plots at 12V. The third plot shows the transient response of the exciton density due to a 12V square voltage pulse of 0.5us. Since the exciton density is proportional to the Electro-Luminescence (EL) intensity, the generic features of the simulated exciton density transient curve are similar to that of an EL curve.

Lastly, the final plot is a transient response of the anode current. The transient response of the anode current is characterized by a sharp charging spike due to the capacitance of the device followed by a quasi-steady state. At turn-off, there is a sharp discharging spike followed by some decay. The current spikes seen in this plot are due to capacitances of the OLED structure. These transient current spikes may affect timing requirements and also the power consumption, thus, degrading the performance of the OLED device.

To load and run this example, select the Load example button in DeckBuild. This will copy the input file and any support files to your current working directory. Select the run button to execute the example.