SLIDE 1
PVMD
Delft University of Technology
Additional optical loss mechanisms
p++ p++ Al Al n+ Al
4 1 2 3 3
p-type c-Si
- 1. Shading
- 2. Reflection
- 3. Parasitic absorption
- 4. Transmission
PVMD Miro Zeman Delft University of Technology Additional optical - - PowerPoint PPT Presentation
PVMD Miro Zeman Delft University of Technology Additional optical - - PowerPoint PPT Presentation
Additional optical and electrical losses PVMD Miro Zeman Delft University of Technology Additional optical loss mechanisms 2 3 1 1. Shading Al Al n + 2. Reflection p-type 3. Parasitic absorption c-Si 3 4. Transmission p ++ p ++ Al
SLIDE 2
SLIDE 3
Shading losses
Metal back electrode Metal front electrode
Semiconductor
Different patterns of front electrode The active area coverage factor, Cf:
SLIDE 4
Shading losses and electrical losses
R= Resistance ρ= resistivity L= length W= width H= height
Busbars Fingers
SLIDE 5
Metal grid design
SLIDE 6
IBC Solar Cells
sunpower
SLIDE 7
Reflection losses
Different refractive indices at interfaces
7
2 1
~ ~ n n
Semiconductor
Metal back electrode Metal front electrode
31 . 5 . 004 3 . 5 045 . 3 . 3
2
i i R
2 2 1 2 1
~ ~ ~ ~ n n n n R
Fresnel equation:
λ=500nm ñ1=1+i0 (air) ñ2= 4.3+i0.045 (silicon) Exercise:
SLIDE 8
Reducing Reflection
Semiconductor
n0 n2 n1, d1
ARC Semiconductor
n2 n0
ARC
SLIDE 9
Transmission losses
d T exp
Transmittance: c-Si (400 nm)=105 cm-1 (800 nm)= 103 cm-1 1 m of c-Si T(400 nm)=exp(-105×10-4)≈0 T(800 nm)=exp(-103×10-4)=0.90
SLIDE 10
Additional electrical losses: fill factor
Isc Voc V I Peak Power Pmax [Wp] P=I×V P
I sc
- c
I mp mp I
P FF I V P I V P P
max
Conversion efficiency
Pmax Imp Vmp FF =
SLIDE 11
Series Resistance (RS)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
- 400
- 300
- 200
- 100
100 200
Voltage [V] Current Density [A/m2]
Rp = 1e4 Ohm Voc Rs = 0 Ohm Rs = 2.5 Ohm Rs = 5 Ohm Rs = 7.5 Ohm Rs = 10 Ohm Rs
RS result of:
▪ Bulk resistance of semiconductor ▪ Bulk resistance of metal electrodes ▪ Contact resistance between semiconductor and metal
SLIDE 12
Parallel Resistance (Rp)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
- 400
- 300
- 200
- 100
100 200
Voltage [V] Current Density [A/m2]
Rs = 0 Ohm Voc Rp = 0.001 Ohm Rp = 0.005 Ohm Rp = 0.01 Ohm Rp = 0.03 Ohm Rp = 1e4 Ohm Rp
RP result of:
▪ Leakage across P-N junction around the edge ▪ Crystal defects, pinholes, impurity precipitates
SLIDE 13
Collection loss
13
Surface recombination S [cm/s] surface recombination velocity
S = 104 cm/s S = 105 cm/s
Bulk recombination
p++ p++
n+ Al p-type c-Si Al Al n U
S bulk
1 1 1
Effective minority carrier lifetime: U [s-1]: recombination rate
SLIDE 14
Recap
Shading loss: ▪ metal electrode coverage Reflection: ▪ different refractive indices Transmission and parasitic absorption: ▪ finite thickness of a cell ▪ absorption coefficient ▪ supporting layers Transmission and parasitic absorption: Collection losses: ▪ bulk recombination ▪ surface recombination
p++ p++ Al Al SiO2 Al p-type c-Si
Fill factor, FF: ▪ Series and shunt resistances
n+