Investigation on N-PERT Bifacial

Solar Cell and Module

Dr. Feng Li

Deputy General Manager of Technology Center

Yingli Energy (China) Co., Ltd

2

Outline

2 N-PERT SBSF Cell Investigation

3 PANDA Cell Module

4 Summary

Slective back surface field(SBSF) solar cell 1 PANDA－N-PERT Cell

3

N-PERT Cell

Diffusion / Ion Implantation

Edge Isolation

SiN Passivation /

ARC Coating

Drying & Firing

Texture

SP Al / Ag

B and P diffused regions made by

different technologies (two diffusions,

co-diffusion using doped glasses, ion

implantation with anneal)

Most of existing P-type Si cell process

technology can be used

Passivation

Passivation

18.0%

18.5%

19.0%

19.5%

20.0%

20.5%

21.0%

21.5%

2009 2010 2011 2012 2013 2014 2015 2016 2017

Yingli Panda Cell Efficiency

4

PANDA － N-PERT Cell

CZ N-Si Substrate

Front contact

Rear contact (Ag)

Incident

light

Incident

light Textured front surface with antireflection coating

Boron diffused emitter (P+)

Textured front surface with antireflection coating

Boron diffused emitter (P+)

Phosphorus diffused BSF

SiNx passivationcoating

Simple cell structure and easy manufacture

Cost-effective production steps and compatible with existing production lines

Sun-light can be accepted by double sides, produce more electricity

Excellent anti-LID performance

Front

Four Busbars

Metallization

Ion

implantation

Double

Printing

Rear

Polishing

Rear

5

N-PERT SBSF Cell Investigation

Conventional back surface field Selective back surface field (SBSF)

Low contact resistance

High back surface recombination

velocity

Low contact resistance

Low back surface recombination

velocity

ARC:SiO2/SiNx

N-type Substrate

(P+) emitter

N+ BSF

n++ n++ n++

Back contact(Ag)

Front contact(Ag/Al) ARC:SiO2/SiNx

N-type Substrate

(P+) emitter

N+ BSF

Back contact(Ag)

Front contact(Ag/Al) ARC:SiO2/SiNx

ARC:SiO2/SiNx

Sample

preparation

Test procedre

N-type Substrate

(P+) emitter

N+ BSF

n++ n++ Depth

Mask Width

Depth

BSF passivation

Voc Jsc FF

Efficiency

Mask width

Alignment

N-PERT SBSF Cell Investigation

Voc Jsc FF

Efficiency

6

7

BSF doping profile Sheet resistance Vs. etching time

Thermal treatment has great impact not only on the Rsheet but also on the

doping profile

Increasing rate of Rsheet is related to the doping profile

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

1E15

1E16

1E17

1E18

1E19

1E20

1E21

surf

ace

phosp

hours

conce

ntr

atio

n(a

tom

s/cm

3)

Depth(um)

POCl3 diffusion 40Ω/sq

POCl3 diffusion 16Ω/sq

0 1 2 3 4 5 6 7 8 9 10

0

20

40

60

80

100

120

140

160

180

200

220

240

Rsh

(Ω/s

q)

Etch time(min)

POCl3 diffusion 40Ω/sq

POCl3 diffusion 16Ω/sq

N-PERT SBSF Cell Investigation

Doping and etch back

8

10 20 30 40 50 60 70 80

650

652

654

656

658

660

662

664

Voc

Jsc

Rsh(Ω/sq)

Voc(

mV

)

38.0

38.2

38.4

38.6

38.8

39.0

Jsc

(mA

/cm

2)

10 20 30 40 50 60 70 80

79.0

79.5

80.0

80.5

81.0

FF

Eff

Rsh(Ω/sq)F

F(%

)

20.0

20.1

20.2

20.3

20.4

20.5

Eff

icie

ncy

(%)

Suitable etching depth has to be selected for balancing the Voc, Jsc

and FF that have great effect on the final cell efficiency

Cell parameters Vs. Rsheet

N-PERT SBSF Cell Investigation

Group Mask width(um) Voc(mV) Jsc(mA/cm2) FF(%) Eff(%)

G1 6a 657 39.17 80.73 20.78

G2 5a 659 39.21 80.66 20.84

G3 4a 661 39.26 80.65 20.93

G4 3a 660 39.30 80.62 20.91

Etch back Metalization 9

N-PERT SBSF Cell Investigation

Mask width optimization

Group Finger

number

Mask

width(um)

Voc

(mV)

Jsc

(mA/cm2)

FF

(%)

Eff

(%)

G1 Normal N-PERT 653 38.85 80.43 20.40

G2 n1 A1 662 39.35 79.54 20.72

G3 n2 A2 661 39.31 80.12 20.83

※Same mask area for G2 and G3

10

N-PERT SBSF Cell Investigation

Mask width optimization

77.5

78.0

78.5

79.0

79.5

80.0

80.5

81.0

81.5

82.0

G3G2

G1

G2

G3

FF

(%)

G1

Group Voc (mV) Jsc (mA/cm2) FF (%) Eff (%)

N-PERT Cell 656 38.98 80.95 20.70

SBSF Cell 662 39.62 80.91 21.22

11

N-PERT SBSF Cell Investigation

Cell performance comparison

400 500 600 700 800 900 1000 1100 12000.0

0.2

0.4

0.6

0.8

1.0

IQE

Wavelength(nm)

Panda Cell

SBSF Cell

19.5 20.0 20.5 21.0 21.5

5%

10%

15%

20%

25%

30%

N-PERT Cell

N-PERT SBSF Cell

Cell efficiency(%)

12

N-PERT SBSF Cell Investigation

Cell Parameters Area(cm2) Voc (mV) Jsc(mA/cm2) FF(%) Eff(%)

Front Side 244.3 664.3 40.01 80.95 21.52

Rear Side 244.3 661.6 36.53 80.87 19.54

0

1

2

3

4

5

6

0

1

2

3

4

5

6

7

8

9

10

0 0.2 0.4 0.6 0.8P

ow

er

(w)

Cu

rre

mt

(A)

Voltage (V)

Front side I-V Curve

0

1

2

3

4

5

6

0

1

2

3

4

5

6

7

8

9

10

0 0.2 0.4 0.6 0.8

Po

we

r (w

)

Cu

rre

mt

(A)

Voltage (V)

Rear side I-V Curve

Typical cell parameters

Bifaciality factor > 90%

LID characteristics

13

Excellent anit-LID performance

PANDA Module

PROPRIETARY AND CONFIDENTIAL

Gain of power output from Panda module compared to traditional mono c-Si solar cell module

One Month Data

Average Gain of Power Output Maximum Gain of Power Output

20.20% 33%

PANDA Module

0

2

4

6

8

10

12

14

16

0%

5%

10%

15%

20%

25%

30%

35%

2015/8

/15

2015/8

/16

2015/8

/17

2015/8

/18

2015/8

/19

2015/8

/20

2015/8

/21

2015/8

/22

2015/8

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2015/8

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2015/8

/25

2015/8

/26

2015/8

/27

2015/8

/28

2015/8

/29

2015/8

/30

2015/8

/31

2015/9

/1

2015/9

/2

2015/9

/3

2015/9

/4

2015/9

/5

2015/9

/6

2015/9

/7

2015/9

/8

2015/9

/9

2015/9

/10

2015/9

/11

2015/9

/12

2015/9

/13

2015/9

/14

Rad

iati

on

of

titl

ed

su

rface

(k

Wh

/m2)

Po

wer

Gain

(%

)

Generating Test

Power Gain

Radiation of titled surface (kWh/m^2)

PANDA Module

15

Power output collection for 1 year with installed modules on a bright rooftop

The distance from module to the ground of 30 cm

The test result shows the Panda module average power output is 21% higher

than normal module .

STC power

output

increased

5% 10% 15% 20% 25% 30%

290 W 304 W 319 W 333 W 348 W 362 W 377 W

Power output gain comparison

Power gain under different reflective conditions

16

Sand/Gray Cement Snow Field Grassland Bright Rooftop

PANDA Module

10% power output gain at the ground and grassland with reflectivity of 25%

15% power output gain at the Sand/gray cement floor with reflectivity of 50%

25% power output gain at the bright rooftop with reflectivity of 78%

30% power output gain at the snowfield with reflectivity of 90%

17

PANDA Module

Panda Module Normal Module

Panda Module Normal Module

Self-cleaning function

Summary

YINGLI N-PERT bifacial cell with SBSF structure have already reached

efficiency of 21.52%, and 19.54% on rear side.

There are still many rooms to improve the N-PERT solar cell performance

such as doping, passivation and metallization. Manufacturing technique

aiming to 22% efficiency of N-PERT cell with bifaciality > 95% is under

investigation and will be realized at YINGLI soon.

YINGLI PANDA module with excellent anti-LID performance provides 10%

- 30% output gain compared to monofacial module depending on ground

reflective conditions.

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