Topology optimization and the basic of
quantum mechanics
Applications
Quantum well solar cells
Quantum dot solar cells
Future works
Time-independent Schrodinger equation:
−
d
2
2
ψ
m dx
2
2
+
V
ψ ψ
E
=
Which is a wave equation and similar with
that of the Electric-magnetic equation. So we
will try to extend the method of optimizing
EM field to the quantum field.
For a periodic potential,
V x a
+
(
)
=
V x
( )
The wave function satisfies
ψ
(
ψ
x a
+
)
=
e
iKa
ψ
x
( )
The solutions of the energy is then a band gap structure
nE
First we can use the following potential as an example
V
V0
x
The electric structure of this periodic potential will be a band gap
structure. The relative band gap between band n and n+1 can be
written as
E
Δ
n
E
0
n
=
2
min :
min :
E
n
E
n
−
+
1
+
1
+
max :
max :
E
n
E
n
( )V x
Using potential as design variable and as the objective
function, we can do the topology optimization procedure to make it
maximum or minimum.
E
Δ
n
E
0
n
In QWSC, the lattice mismatch between the
two materials leads to misfit strain in the well,
which is reported to have a negative effect on
the transition efficiency. Ekins – Daukes
(2001) et al. developed the stress-balance
method to reduce this effect.
The thicknesses of materials 1 and 2 are
selected appropriate such that the lattice
constants satisfy
According to the experiments of Ekins-Daukes, the efficiency is
remarkably improved by strain-balance, and the dark-current is much
weaker than the former method. So strain-balanced quantum well is
mostly adopted in current studies about QWSC.
But
there are still other problems. For
example, given two kinds of materials, the
thickness of each layer in the quantum well is
fixed if we make the strain balanced. While in
fact the thickness is also an important factor
(Bercowicz et al., 2000; Chen et al., 2008),
when the strain is balanced, the efficiency
may be not the highest.