organic device simulation using silvaco software
TRANSCRIPT
Organic Device Simulation Using Silvaco Software
Organic Device Simulation Using Silvaco Software
• Introduction – Silvaco TCAD Simulator • Theory – Models • OTFT Simulation v.s Measurement • OLED Simulation v.s Measurement • Bilayer TPD/Alq3 OLED Example • Transient Simulation of OLED Pixel • Summary
Organic Devices Simulation: Contents
- 2 -
Organic Device Simulation Using Silvaco Software
• Athena- 2D Process Simulator • Atlas – Device Simulator
• S-Pisces – Silicon material Drift-Diffusion Simulator • Blaze – Hetero-interfaces (Compound Semiconductor) Materials Simulator • TFT – a-Si/poly-Si TFT Device Simulator • OTFT – Organic TFT Simulator • OLED – Organic Light Emitting Diode Simulator
Organic Devices Simulation: Silvaco’s TCAD Software
- 3 -
Organic Device Simulation Using Silvaco Software
• Metal & Semiconductors: charge transport is limited by scattering of the carriers, mainly due to thermally induced phonons and lattice deformations. Transport is limited by phonon scattering. Charge mobility decreases with temperature
• Organic materials: transport occurs by phonon assisted hopping of charges between localized states. Charge mobility increases with temperature
• General mobility model of organic material : • Poole-Frenkel field-dependent mobility
Organic Devices Simulation: Transport Mechanisms
- 4 -
Organic Device Simulation Using Silvaco Software
• Charge Injection (metal contact) • Ohmic (Dirichlet boundary condition) • Schottky contact (injection limited current) :
• thermionic emission model - tunneling • interface barrier lowering
• Transport model(bulk) • Band-like transport model (organic molecular crystals: pentacene, tetracene) at low T. • Space-Charge-Limited Current(SCLC): Poisson + Current continuity equations • Hopping transport in disordered organic semiconductor
• Density of States • Poole-Frenkel Mobility
Organic Devices Simulation: Organic Transport Theory For Simulation
- 5 -
Organic Device Simulation Using Silvaco Software
• Poisson Equation
• Current Continuity Equations
• Drift Diffusion Equations
Organic Devices Simulation: Classical Theory Of Charge Transport – Drift Diffusion Model
- 6 -
Organic Device Simulation Using Silvaco Software
• Density Of States (DOS)
• Trapped Charge
Organic Devices Simulation: Density Of State & Trapped Charge – Organic Defects
- 7 -
Organic Device Simulation Using Silvaco Software
• Probability of Occupation
• Steady State: Recombination/Generation
(SRH)
Organic Devices Simulation: Organic Defects
- 8 -
Organic Device Simulation Using Silvaco Software
Organic Devices Simulation: Poole-Frenkel Mobility Models
- 9 -
Organic Device Simulation Using Silvaco Software
• Langevin Radiative Rate
• Singlet Exciton
Organic Devices Simulation: Langevin Recombination Rate & Exciton Rate Equations
- 10 -
Organic Device Simulation Using Silvaco Software
• Triplet Exciton
where
Organic Devices Simulation: Langevin Recombination Rate & Exciton Rate Equations (con’t)
- 11 -
Organic Device Simulation Using Silvaco Software
• Time-of-flight(TOF) method • SCLC method • Field Effect Transistor(FET) method
Atlas – Organic Device Simulation: Mobility Simulation
- 12 -
Organic Device Simulation Using Silvaco Software
Atlas – Organic Device Simulation
- 13 -
Measurement vs. Simulation
Density of States
µp-0.62
Organic Device Simulation Using Silvaco Software
Transfer curve: linear & sqrt(Ids)
Atlas – Organic TFT Device Simulation
Hole concentration distribution and current flow lines in the OTFT device.
- 14 -
Organic Device Simulation Using Silvaco Software
• Metal/Organic Interface injection
Atlas – Organic LED Device Simulation: OLED Example
- 15 -
I.D. Parker J.Appl. Phys. 75(3),1 Feb 1994, p.1656
Organic Device Simulation Using Silvaco Software
• Injection - Calcium • Ca(2.9eV) is better than other cathode metal.
Atlas – Organic LED Device Simulation
- 16 -
Simulated
Measured
Organic Device Simulation Using Silvaco Software
Atlas – Organic LED Device Simulation: High-Efficient Amorphous OLED
- 17 -
Fraction of injected charge that form excitons
Organic Device Simulation Using Silvaco Software
• Exciton Profile
Atlas – Organic LED Device Simulation: Bilayer TPD/Alq3 OLED Example: Singlet Exciton Density Profile
- 18 -
Organic Device Simulation Using Silvaco Software
Atlas – Organic LED Devices Simulation: Bilayer TPD/Alq3 OLED Example: IL & Internal Efficiency
- 19 -
IL curve Internal Efficiency
Organic Device Simulation Using Silvaco Software
Atlas – Organic LED Device Simulation: Bilayer TPD/Alq3 OLED Example: Optical Output Coupling
- 20 -
n=1.5
n=1.9
n=1.8
Organic Device Simulation
Transient Simulation of OLED Pixel
Organic Device Simulation Using Silvaco Software
• A p-type poly-Si TFT AM-OLED pixel is shown
• The cathode and anode electrodes of the OLED form an intrinsic capacitance C and the resulting equivalent circuit is shown
• When it is connected to a poly-Si TFT with an on resistance RON, it forms a circuit with its speed limited by the RC time constant
Organic Devices Simulation: Basic OLED Equivalent Circuit
- 22 -
Organic Device Simulation Using Silvaco Software
• The device simulation structure of a p-type Poly-Si TFT AM-OLED pixel is shown here
• The structure is set up for device simulation and does not represent actual process steps
• More complicated OLED pixels can be simulated using Atlas MixedMode
Organic Devices Simulation: Corresponding OLED Pixel Structure
- 23 -
Organic Device Simulation Using Silvaco Software
• Curve 1: Transient current simulation results of the PPV OLED only (in blue)
• Curve 2: The combined poly-Si TFT/OLED pixel (in black) – note the effect of TFT on current level
• The rise/fall (ON/OFF) signal is coupled through the poly-Si TFT and is converted as a current spike in the OLED as shown
Organic Devices Simulation: OLED Pixel Simulation
- 24 -
Organic Device Simulation Using Silvaco Software
• The transient OLED current density response due to a 600ns square data voltage pulse of the experimental and simulation curves are 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
* Pinner et al, J Appl Phys 86 (9) 5116
Organic Devices Simulation: OLED Experiment
- 25 -
Organic Device Simulation Using Silvaco Software
• A simulated transient result of the exciton density is shown
• The exciton density assumes a Langevin recombination process and takes into account singlet excitons, inclusive of diffusive and decay terms
Organic Devices Simulation: Exciton Simulation
- 26 -
Organic Device Simulation Using Silvaco Software
• One can observe the fast initial EL rise followed by a slower rise, fast modulation in the turn-off, and a decaying exponential tail
• Assuming the exciton density is proportional to EL, note the similar shape of the previous exciton density simulation with the EL curve
* Pinner et al, J Appl Phys 86 (9) 5116
Organic Devices Simulation: Experimental EL Curve*
- 27 -
Organic Device Simulation Using Silvaco Software
Organic Devices Simulation: OLED Langevin Recombination Zone (2D plot)
- 28 -
Organic Device Simulation Using Silvaco Software
• Calculation of transient OLED Langevin recombination and exciton density based on 3 pulses
Organic Devices Simulation: Langevin Recombination and Exciton Density
- 29 -
Organic Device Simulation Using Silvaco Software
Organic Devices Simulation: PPV OLED Exciton Density (2D plot)
- 30 -
Organic Device Simulation Using Silvaco Software
Organic Devices Simulation: Extraction of OLED Internal Efficiency
- 31 -
IV-Curve Internal Efficiency Curve
Organic Device Simulation Using Silvaco Software
• Organic Materials: • Default Bandgap parameters. Others are defined by user-defined • Density-Of-States(DOS)
• Transport: Drift-Diffusion/Poole-Frenkel mobility model • Bimolecular Langevin Recombination • Excition Rate Equation: singlet/triplet exciton profiles
• Radiative rate for luminescence or phosphorescence
• Reverse Ray-Tracing: external efficiency (refractive index step) • Angular power plot/optical output coupling coefficient/near&far field distribution
Summary
- 32 -