12 mihailetchi ok

ZEBRA: bifacial IBC technology

Valentin D. Mihailetchi, Andreas Halm, Corrado Comparotto, Severin Aulehla,

Radovan Kopecek

International Solar Energy Research Center e.V., Konstanz, Germany

Mihailetchi et.at., bifiPV workshop, Chambery, May 2014

Outline

2

General

• Bifacial cells and modules

• ISC Konstanz bifacial cell concepts

• BiSoN: n-PERT cell technology

• ZEBRA: IBC cell technology

Indoor STC results (front vs. rear illumination)

• IV data

• Spectral Response

• Comparisons, predictions, …

• BiSoN and ZEBRA modules

Outdoor test results

• ZEBRA vs. BiSoN (IBC vs. n-PERT)

Summary

Mihailetchi et.at., bifiPV workshop, Chambery, May 2014 3

n-type solar panels producers on the market:

Producer Cell technology

Cell efficiency

Module efficiency

SunPower

IBC (Maxeon)

>24% 21.5% Monofacial cells

Panasonic HIT 22.0% 19.4% Bifacial cells

Yingli

n-PERT (Panda) 19.5% 17.1% Bifacial cells

PVGS

n-PERT (EarthOn) 19.5% 16.2% Bifacial cells and panels

LG

n-PERT (NeoN) 21.3% 18.3% Bifacial cells

Bifacial cells and modules

Screen printed metallization


n-type solar panels producers on the market:

Producer Cell technology

Cell structure

SunPower IBC (Maxeon)

Monofacial cells

Panasonic HIT Bifacial cells

Yingli n-PERT (Panda)

Bifacial cells

PVGS n-PERT (EarthOn)

Bifacial cells and panels

LG n-PERT (NeoN)

Bifacial cells

Bifacial cells and modules

All (produced) bifacial cells have both sides contacts (BSC) !!


Is BSC the ultimate bifacial cell technology ?

Bifacial cells and modules front side rear side


ISC’s bifacial cell concepts BiSoN (n-PERT)

• BSC cell technology

• n-type 6-inch Cz Si

• homogeneous p+ and n+ diffusions

• front side textured, rear side flat

• IBC cell technology

• n-type 6-inch Cz Si

• homogeneous p+ and n+ diffusions

• front side textured, rear side flat or textured

ZEBRA (IBC)


ISC’s bifacial cell concepts

BBr3 diffusion, p+ emitter

POCl3 diffusion, n+ BSF

Saw damage etching, alkaline texturization, cleaning steps

SiO2/SiNx passivation & ARC

Screen printing and firing of p and n fingers, busbars

PECVD masking

Laser ablation

BiSoN (n-PERT)

ZEBRA (IBC)


ISC’s bifacial cell concepts BiSoN (n-PERT)

ZEBRA (IBC)

What if both cell concepts cost the same (in €/Wp)?


IV data

Cell type area

[ cm2 ]

JSC

[ mA/cm2 ]

VOC

[ mV ]

FF

[ % ]

h

[ % ]

Pmax

[W]

239 39.4 652 78.9 20.3* 4.85

239 41.2 646 79.1 21.0 5.03

IV measurements of best cells (front side illumination):

- on a reflective chuck

*Independently confirmed by CalLab PV cells at Fraunhofer ISE


IV data

Cell type illumination JSC

[ mA/cm2 ]

h

[ % ]

Pmax

[W]

Metallization area

[ % ]

front 39.3 20.1 4.8 6.3 ± 0.24

rear 34.7 17.6 4.2 7.7 ± 0.32

front 40.8 20.9 5 0

rear 30.5 n/a(15.6*) n/a(3.7*) 17.5 ± 0.64

IV measurements of best cells (front and rear side illumination):

- on a black coated chuck

Is ZEBRA cell concept interesting for bifacial applications?

? OK *Estimated value assuming the same Voc and FF from front side illumination


IQE data IQE measurements from front and rear side:

1. front side response: ZEBRA BiSoN

2. rear side response: ZEBRA < BiSoN

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.20.00.10.20.30.40.50.60.70.80.91.0

BiSoN (front) BiSoN (rear) ZEBRA (front) ZEBRA (rear)

IQE

(-)

Wavelength (µm)


Comparisons, predictions IV measurements of best cells (front and rear side illumination):

ƞ rear / ƞ front = 75 % ƞ rear / ƞ front = 87.5 %

1. ZEBRA is the best for front side illumination

2. BiSoN has the best bifacial ratio

BiSoN ZEBRA

15

16

17

18

19

20

21

Effic

ienc

y (%

)

rear illumination

front illumination

(5 W)

(4.8 W)


BiSoN and ZEBRA modules

STC indoor measurements (25°C, 1 sun)

illumination Pmax

[W]

Prear/Pfront

(module)

Prear/Pfront

(best cell)

Front 17.68 0.88 0.87

rear 15.71

front 18.22 0.65* 0.75**

rear 11.84*

4 cells modules with transparent back sheet:

Front side photograph

Front side photograph

* with 3 mm wide ribbons (24% shaded area)

** estimated from JSC(rear)/JSC(front)


Comparisons, predictions Calculated modules performance with additional rear side illumination:

1. ZEBRA is as good as a dedicated bifacial module for rear side light intensities <0.3 sun.

2. ZEBRA has the advantage of generating more power in monofacial or at low albedo contributions

0.0 0.1 0.2 0.3 0.4 0.517

18

19

20

21

22

23

24

25

26

rear side light intensity (suns)

4 ce

lls m

odul

e po

wer

(W) BiSoN, 2mm ribbons (Prear/Pfront=88%)

ZEBRA, 3mm ribbons (Prear/Pfront=65%) ZEBRA, 2mm ribbons (Prear/Pfront=75%)


Comparisons, predictions

Cells (or modules) fabrication:

• can have asymmetric front/rear performance

• should be optimized based on front side performance

Reflected sunlight

Direct sunlight

Slanted

Reflected sunlight

Direct sunlight

Horizontal

Direct light

Reflected light >

Typical outdoor installation of a bifacial module:

rear side irradiance ≤ 0.3 × front side irradiance !?


Outdoor test results Outdoor test conditions of the 4-cells modules:

• ground reflectivity → 70% (300-1200nm) (white back sheet) • orientation and inclination → South, 30° • measurement interval → every 5 min. (10 sec. module measure time) • all modules assumed to have the same temperature during an IV scan • front glass taped black outside cell area • one additional module was used to measured the back side light intensity

Photograph of the outdoor setup

ZEBRA black BS

ZEBRA transparent BS

ZEBRA (rear irradiance)

BiSoN transparent BS

BiSoN black BS

ZEBRA (2) transparent BS


Outdoor test results

15-May-1416-May-14

17-May-1418-May-14

19-May-1420-May-14

21-May-140

200

400

600

800

1000

1200

1400D

irect

irra

dian

ce (W

/m2 )

One sunny day chosen for modules comparison !

Outdoor test conditions of the 4-cells modules:


Outdoor test results Outdoor modules performance (bifacial versus monofacial):

Module temp. at noon: 48°C !!!

1. Monofacial modules: ZEBRA = BiSoN

2. Bifaical modules: ZEBRA ≤ BiSoN

08:00 10:00 12:00 14:00 16:00 18:00

0.10.20.30.40.50.60.70.80.91.01.1

ZEBRA (transparent BS) ZEBRA (black BS) Bison (transparent BS) Bison (black BS) Direct irradiance (suns) Indirect irradiance (suns)

time (HH:mm)

P max

/Pm

ax (S

TC) (-

)


Outdoor test results One day yield comparison (bifacial versus monofacial):

0.26

0.28

0.30

0.32

0.34

0.36

Ener

gy y

ield

(Wh/

Wp)

BiS

oN

blac

k B

S

BiS

oN

tran

spar

ent B

S

ZEB

RA

blac

k B

S ZEB

RA

tran

spar

ent B

S

+ 15.1%

+ 19.8%

08:00 10:00 12:00 14:00 16:00 18:005

101520253035404550 Bifacial gain:

BiSoN ZEBRA

Irradiance: Indirect/Direct

time (HH:mm)

(%)

ZEBRA is a bifacial IBC technology !!!


Summary

Best cell efficiency: 20.3%, n-PERT BiSoN 21.0%, IBC ZEBRA

Bifaciality ratio (@ cell level):

87.5%, n-PERT BiSoN 75.0%, IBC ZEBRA

Bifacial/Monofacial yield gain:

19.8%, n-PERT BiSoN 15.1%, IBC ZEBRA

Acknowledgements: The project HERCULES has received funding from the European Union’s Seventh Programme for research,

technological development and demonstration under grant agreement No 608498.

12 mihailetchi ok

Presentations & Public Speaking