Low Light Intensity Performance of N- and P-Type ... - ISC Konstanz

LOW LIGHT INTENSITY PERFORMANCE OF N-
AND P-TYPE SILICON SOLAR CELLS WITH
DIFFERENT ARCHITECTURES
Andreas Halm, Peter Hering, Corrado Comparotto, Valentin D.
Mihailetchi, Eckard Wefringhaus, Radovan Kopecek
International Solar Energy Research Center - ISC - Konstanz,
Germany
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 1

contents
• motivation – potential advantage of n-type
solar cells and modules
• lV measurements of p- and n-type cells at
low light intensities
• influence of the shunt resistance
• outdoor module measurements
• summary
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 2

motivation
N-type on wafer level: n-type base material maintains high lifetimes for
low injection levels at the presence of common impurities like Fe
• n-type FZ: D. Macdonald et al., APL Vol 85 Nr
18, p. 4061-4063, 11.2004
• n-type mc: S. Dubois PhD thesis
more relevant on cell level: diffusion length LD
Effective
carrier density
[1/cm³]
LD p-type
[µm]
LD n-type
[µm]
1e15 312 304
2e14 240 298
S. Dubois, PhD thesis, 2006, INES, France
-> potential advantage of n-type base on cell level
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 3

IV measurements
illumination: 1 sun …….. 0.02 suns (5 steps)
base material: Cz p-type Cz n-type
cell design:
standard:
Al BSF cell
Al rear emitter cell
advanced:
PERL cell
PERL cell
-> comparison of the relative normalized power output at P mpp
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 4

IV measurements – standard cells
definition:
• P mpp @ 1 sun ≡ 1
-> normalization for comparability
cell to cell
• P mpp relative to illumination:
P mpp,rel = P mpp (x)*(1sun/x suns)
-> for comparability of different
illumination levels
-> P mpp,rel drops faster for p-type cells !
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 5

IV measurements – PERL cells
definition:
• P mpp @ 1 sun ≡ 1
-> normalization for comparability
cell to cell
• P mpp relative to illumination:
P mpp,rel = P mpp (x)*(1sun/x suns)
-> for comparability of different
illumination levels
-> P mpp,rel drops faster for n-type cells !
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 6

influence of parallel resistance
• P mpp,rel drops linear with
the shunt resistance
• saturation observable for
R shunt ~ 1 M cm²
• minimum drop of P mpp,rel :
13% for n-type
( R shunt = 3 M cm² )
20% for p-type
( R shunt = 25 k cm² )
-> Rshunt governs the power output for low illumination levels !
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 7

origin of power loss without R shunt
-> drop of P mpp,rel directly proportional to Voc drop for R shunt > 1Mcm²
-> logarithmic behavior according to Voc = kT/q * ln(I phot /I R +1)
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 8

simulated influence of R shunt
Silvaco ATLAS simulation :
• ideal cell device including
Rseries and Rshunt
• no Rcontact considered
• extraction of IV parameters
at 0.02 suns with varying
Rshunt
-> good agreement of
experiment and simulation
-> simulation confirms that for
Rshunt > 1 Mcm² no
more significant effect on
the IV parameters is
observed
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 9

outdoor module measurements
• 4 cell mini-modules made of cells of the same batches as used before:
standard BSF p / Al emitter n – PERL p / PERL n
• modules are measured in two configurations:
• transparent backsheet with white back relfector on floor
• for this study: black backsheet taped on the rear side of each
module
• intensity E [W/m²] measured every 20s using a pyranometer
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 10

elative power output outdoors
• only data points between 9.45 am and 4.45 pm are considered because
of shadowing problems
• calibrated flasher measurements after LID of each module are used as
reference
‣ all n-type modules show higher relative power output for all intensities !
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 11

P mpp,rel vs. intensity outdoors
For 8 < E < 50 W/m² :
module data is consistent with cell data: R shunt limits P mpp,rel
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 12

Pmpp,rel vs. intensity outdoors
For 50 < E < 150 W/m² :
P mpp,rel independant of R shunt !
-> influence of effective module temperature and lifetime is visible !
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 13

P mpp,rel vs. intensity outdoors
For 8 < E < 1200 W/m² :
P mpp,rel for all n-type modules is higher than for the p-type references !
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 14

comparison of energy harvest
-5.4%
-4.5%
-1.7%
-0.4%
*
*
*all measurements in monofacial configuration !
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 15

comparison of energy harvest
data source: www.ipe.uni-stuttgart.de
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 16

summary
L eff
p-type
R shunt L eff higher
n-type
higher
S. Dubois, PhD thesis, 2006, INES, France
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 17

summary
• the low light performance of Si solar cells strongly
depends on the R shunt rather than the base material
• on module level R shunt influences the power output for
intensities lower 50 W/m²
• n-type modules feature a higher energy yield due to
better temperature coefficient and higher carrier lifetimes
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 18

acknowledgements
• “Schwachlicht”- project (grant reference
KF2818601AB1) by the German
government (BMWi) under the ZIM program
• Hitachi Chemical Co. Ltd. for stringing the Al emitter
cells
• PI Berlin for module measurements
• ISC members for support:
• Lejo J. Koduvelikulathu for simulations
• Antonia Beuttner for measurements
Andreas Halm, PVSEC-21 Fukuoka, Japan, 2011 19