Download Slide 1

A New Design Tool for Nanoplasmonic Solar Cells
using 3D Full Wave Optical Simulation with 1D
Device Transport Models
Liming Ji* and Vasundara V. Varadan
Microwave& Optics Laboratory for Imaging & Characterization
University of Arkansas
* [email protected]
Optimization of Nanoplasmonic Structure Designs
Objective
1D Carrier Transport Model
Integrate 3D full wave simulation with 1D carrier transport model to calculate the efficiency of nanoplasmonic solar cells.
 The AMPS 1D code is used for the numerical calculation of carrier transport in solar cells.
 The dimension of each nanosplasmonic solar cell needs optimization to achieve the best performance for the solar cell.
 Two challenges for optimization work:
1) Numerical simulations are slow. Compared to the wavelength λg in each medium, the size of a thin film solar cell is usually
> 5 λg at 300 nm. Speed is a very important issue especially for finite element simulations.
2) The optimization has to follow some guidelines.
 AMPS stands for Analysis of Microelectronic and Photonic Structures.
Introduction
 The efficiency of nanoplasmonic solar cells is usually obtained through measurement of fabricated samples.
 Fabricating a nanoplasmonic solar cell is expensive and time consuming.
 The computation of detailed carrier transport is done for the steady state of devices.
Ψ is the electrostatic potential
n & p are free electrons and holes density
nt and pt are trapped electrons and holes
ND+ and NA- are ionized dopings
ε is the permittivity and q is the charge of an electron
Poisson’s Equation
 Numerical simulations can quickly compute the efficiency of solar cells at low cost.
 The available numerical codes for solar cells so far apply only to solar cells with all planar cells and they
cannot account for:
1) The particular distribution of absorbed power inside the semiconductor layer;
2) The influence of the thickness of front and back passivation layers.
Light Absorption of A Solar cell with
different Thickness of Front spacer
 The transmission line model and the concept of effective impedance can be used to describe a solar cell.
AZO L1
Continuity Equation
a-Si L2
Gop is the optical generation rate
R is the recombination rate
Jn and Jp are electron and hole current densities
Plasmonic
Layer L3
Patterns of Localized Electric Field
Incident
Light
The optimization of L1, L2 and Zinput will result in the best
performance of a nanoplasmonic solar cell.
Reflection
AZO
L1
Z1
a-Si:H
L2
Z2
ZInput
Ag
U=0
U=V
0
L
Comparison between Transmission Line
Calculation and Full Wave Simulation
x
 The device is divided into many small segments and the Poisson’s equation, as well as the continuity equations, are solved within
each segment with the help of boundary conditions.
Plasmonics
L3
Z3
From Full Wave Simulation to AMPS
 The finite element High Frequency Structure Simulator (HFSS) is used for full wave simulations.
Methodology
 The efficiency of nanoplasmonic solar cells can be calculated by integrating full wave simulations into the
carrier transport model.
ZAg
 A 3D distribution of absorbed power inside the semiconductor is generated by HFSS and it is converted into a 1D pattern before exporting
into the AMPS program.
1D Power Distribution in Si
x 10
20
High
3D Power Distribution in Si
14
18
7
16
Full Wave Simulation
6.5
14
12
6
10
Yes
Optimization?
5.5
8
Optmization of
Nanoplasmonic Structure
6
 The accuracy can be improved if the 3D power distribution does not have to be converted into 1D distribution.
4
4.5
2
Low
0
No
Obtain Power Distribution
in Semiconductor
Calculate Optical
Generation Rate
Numerical Computation of
Carrier Transport
Future Plan: 3D Carrier Transport Model
5
0.2
0.4
0.6
0.8
1
 The optical generation rate Gop in each small segment for electron-hole pairs are replaced by the imported 1D power distribution.
Convert 3D Power
Distribution into 1D
Pattern
Export 1D Power
Distribution into Carrier
Transport Model
Optical Generation Rate
Calculation
 The key step is to obtain the optical generation rate of carriers in each nanoplasmonic solar cell.
 All derivative equations are three dimensional.
Comparison of the Original and New Methods for Gop Calculation
Original Method
ΦFOR
Rj
New Method
x
x=j
x=j+1
d
d
Gop ( x ) 
 FOR ( x)   REV ( x)
dx
dx
Conclusions
 The efficiency of nanoplasmonic solar cells can be calculated by combining the 1D carrier transport model with 3D full wave simulations
PLOCAL
Rj+1
ΦREV
The carrier generation is dependent on the decreasing rate of
the photon flows.
Output Solar Cell
Efficiency
 The optical generation rate and flow of carriers will have more directional details.
 The optical generation rate of carriers is calculated based on the imported power distribution in the semiconductor.
 The design of nanoplasmonic structure can be further improved by optimization using transmission line theory.
x=j
x=j+1
Gop( x)  PLOCAL ( x)
x
The carrier generation is calculated directly from the localized power
density in each small segment.
ФFOR is the photon flow in the forward direction
ФREV is the photon flow in the forward direction
PLOCAL is the localized power density imported from HFSS
 The J-V curve of the nanoplasmonic solar cell is calculated based on the imported Gop.
 Developing the 3D carrier transport model can further improve the accuracy of the efficiency computation.
Acknowledgement
The authors acknowledge the research support provided by the National Science Foundation under EPS–1003970.
The authors also thank Professor Stephen J. Fonash of the Pennsylvania State University for providing the source code of AMPS 1D.