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Coupled optoelectronic simulation of organic bulk-heterojunction solarcells: Parameter extraction and sensitivity analysisR. Häusermann,1,a E. Knapp,1 M. Moos,1 N. A. Reinke,1 T. Flatz,2 and B. Ruhstaller1,2,b1Institute of Computational Physics, Zurich University of Applied Sciences, Wildbachstrasse 21, 8401 Winterthur, Switzerland2Fluxim AG, Dorfstrasse 7, 8835 Feusisberg, Switzerland
Speaker: Yu-Chih ChengAdvisor: Peichen Yu
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Outline• INTRODUCTION• DESCRIPTION OF THE NUMERICAL DEVICE
MODEL• ESTIMATION OF THE DISSOCIATION RATE• SENSITIVITY ANALYSIS• CONCLUSION
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Outline• INTRODUCTION• DESCRIPTION OF THE NUMERICAL DEVICE
MODEL• ESTIMATION OF THE DISSOCIATION RATE• SENSITIVITY ANALYSIS• CONCLUSION
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INTRODUCTION• Organic Photovoltaic advantages• Planar heterojunction devices and bulk-heterojunction BHJ devices
• The incoupling of light into a multilayer structure
• The extraction of charges needs electrical model
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DA
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Outline• INTRODUCTION• DESCRIPTION OF THE NUMERICAL DEVICE
MODEL• ESTIMATION OF THE DISSOCIATION RATE• SENSITIVITY ANALYSIS• CONCLUSION
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A :Optical modeling
AM 1.5 spectrum is used for I0
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Absorbance
k stands for the complex part of the refractive index
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B. Electrical modeling
• Charge-transfer exciton generation and dissociation
• Charge drift and diffusion• Charge extraction at the electrodesThree things need to be considered
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Wannier exciton
(typical of inorganic
semiconductors)
Frenkel exciton
(typical of organic
materials)
Excitons(bound
electron-hole
pairs)
SEMICONDUCTOR PICTURE MOLECULAR PICTURE
treat excitonsas chargeless
particlescapable ofdiffusion,
also viewthem as
excited statesof the
molecule
GROUND STATE WANNIER EXCITON GROUND STATE FRENKEL EXCITON
binding energy ~10meV
radius ~100Å
binding energy ~1eV
radius ~10ÅElectronic Processes in Organic Crystals and Polymers by M. Pope and C.E. Swenberg
Charge Transfer (CT)Exciton
(typical of organicmaterials)
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1. Charge-transfer-exciton dissociation
• S(x):CT-exciton density
• - recombination term of free charge carrier pairs generates a CT exciton.
• - absorption profile• - photon-to-CT-exciton conversion efficiency• - decay of a CT state • - dissociation of a CT state
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Processes for CT-exciton modeling
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Dissociation probability Pby Onsager–Braun theory
• Key point: and the pair binding energy is calculated under the assumption that CT excitons have the same dependence of the binding energy on the separation distance as ion pairs.
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2. Drift-diffusion modeling
( : 1D Poisson’ eq )
current equation for electrons Einstein relation
r(x) stands for the Langevin recombination
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3. Built-in voltage• debate on the nature of the open-circuit
voltage Voc:• E• the energy of the charge transfer
absorption• work function of the electrodes• Light intensity• Temperature
LUMO
HOMO
D
A
∆𝐸
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4. Charge extraction• This model considers the barrier reduction at an
organic-metal interface due to the electric field and the image charge potential and calculates the net injection current.
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5.Validation of the simulator
• Voc increased slightly with and also depends on the mobility, not equal to the Vbi
• Fill factor influence by recombination , mobility and .
• Jsc depends linearly on until recombination losses take over.
• These results correspond to experimental observations.
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Outline• INTRODUCTION• DESCRIPTION OF THE NUMERICAL DEVICE
MODEL• ESTIMATION OF THE DISSOCIATION RATE• SENSITIVITY ANALYSIS• CONCLUSION
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Parameters extraction
• The two mobility measured the constant mobilities of electrons and holes in a P3HT:PCBM BHJ solar cell depending on the annealing temperature.
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Estimation of unknown parameters
• decay rate • the pair separation distance a• the photon-to-CT-exciton conversion efficiency
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Simplify model
• Assumes that absorbed photons directly generate free e-hole pairs .
• Recombining charges are lost and not fed into the continuity eq.Reduced model:
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• varied between 1 and 0.01 to check the influence of electron
• geff=0.66 is consistent with the analysis
• Fig suggests that recombination efficiency reff in the simplified model is 10% or lower.
• (simple model) corresponds to (full model), P must be 90% or higher.
The dissociation probability P
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• a can be determined under the assumption that is set to
• P must be 90% or higher
• The best fit a has been
chosen to be 1.285 nm
Dissociation probability according to the Onsager–Braun theory depending on the electrical field for several initial pair separation distances a
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• The best fit a has been chosen to be 1.285 nm by comparing experimental current-voltage curves with simulated curves for an active layer thickness of 70 nm
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Outline• INTRODUCTION• DESCRIPTION OF THE NUMERICAL DEVICE
MODEL• ESTIMATION OF THE DISSOCIATION RATE• SENSITIVITY ANALYSIS• CONCLUSION
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A. Thickness dependent sensitivity
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B. Current-voltage curve sensitivity
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Outline• INTRODUCTION• DESCRIPTION OF THE NUMERICAL DEVICE
MODEL• ESTIMATION OF THE DISSOCIATION RATE• SENSITIVITY ANALYSIS• CONCLUSION
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• photon to CT-exciton conversion efficiency geff = 66%.
• lower limit for the CT-exciton dissociation efficiency of 90%
• Adding the measured current-voltage curve to the numerical analysis and assuming that is set to
• the influence of the two exciton parameters and the electron mobility are linearly dependent in the current-voltage curve and photocurrent thickness scaling
CONCLUSION