New selective processing technique for solar cell

Costanza, May 7-8, 2013 M. Balucani

New selective processing technique for solar cell

M. Balucani1,4, K. Kholostov1, P. Nenzi1, R. Crescenzi1,

L. Serenelli2, M. Izzi2, M. Tucci2

D. Bernardi3

D. Ciarniello4

1 DIET-Sapienza University of Rome, Via Eudossiana, 18 - 00184 Roma (ITALY),; 2 ENEA Casaccia Research Centre Rome, ITALY,

3 2BG S.r.l. Padova (ITALY), 4 Rise TechnolgyS.r.l. Roma (ITALY),

2


Outline

•Introduction

•Plating Technology Key Issues

•What we are able to solve and how we do it

•Dynamic Liquid Drop/Meniscus

•Main results achieved

•Conclusions

3


International Technology Roadmap for Photovoltaic (ITRPV)

ed. March 2013

Introduction

4


International Technology Roadmap for Photovoltaic (ITRPV)

ed. March 2013

Introduction

5


Current plating main key issues:

Pin-holes Front side: Ni-Cu adhesion to Si Back side: direct plating on Al Speed of Plating Throughput and Space floor Drag-out Reduce additive consumption

Plating Technology Key Issues Before the introduction of alternative metallization techniques, technical issues

in reliability and adhesion have to be solved. Appropriate equipment also needs to be available (ITRPV)

LIP 0.6-3.0 A/dm2

0.3-0.5 ml/w

6


Pin-hole coloring technique

Plating Technology Key Issues

7


Cu d

eposit

s in v

ery

sm

all p

in-hole

s

Plating Technology Key Issues

8


What we are able to solve…..

Pin-holes Localized Treatment Front side:Ni-Cu adhesion to Si Porous Silicon Back side: direct plating on Al Yes …. Speed of Plating Jet plating : Vfluid=2ms-1

Drag-out Very low...................

9


……..and ……….

The concept of localized plating

LECD (Localized EleCtrochemical

Deposition)

Static Meniscus

[R A Said Nanotechnology 14 (2003) pp. 523–53]

10


How we do it

Dynamic Liquid Drop DLD

11


How we do it

Dynamic Liquid Meniscus DLM

12


Dynamic Liquid Drop/Meniscus

Key d

iffe

rence w

ith a

sta

tic m

enis

cus

13


Dynamic Liquid Multi Drop/Meniscus

14



Gravity influence

Inlet > 8 mm Go Up-side down

15


Rayleigh Taylor instability: When a heavy fluid is supported by a light fluid, the system is RT unstable

Dynamic Liquid Drop/Meniscus: Problem to solve

16


I (µm) W (µm) O (µm) H (µm) Vinlet (ms-1) Δp (Pa)

500 500 500 2000 0,4 2000Nozzles operating

conditions

TEST CFD

60,5 63,9Air volume flow

rate (l/min)

Dynamic drop

height (µm)

Dynamic meniscus

footprint (µm)

570 590

1710 1760


17



18



20m inlet opening

MicroElectroMechanical (MEMS) Technology used to build very small DLD/DLM

19


Dynamic Liquid Drop/Meniscus: how we use it

DLD-DLM configurations for: a) Opening of ARC layer or any kind of etching

b) Porous Silicon formation on n-type doped emitter

c) Electroplating on Porous Silicon region on n-type doped emitter

d) Porous Silicon suitable for n- or p-type doped emitter

e) Electroplating on Porous Silicon region on p-type emitter

20


Main results achieved: Front Side

SEM Cross-Section of Industrial PV cell with porous silicon

ARC opening is done in 3 s

21



a) current density versus time is constant

b) current density is linearly increased versus time

c) PRP (Pulse Reverse Plating) at low current densities (jdir = 20 mA cm-2 jrev = 4 mA cm-2)

d) PRP at high current densities (jdir = 100 mA cm-2 jrev = 20 mA cm-2)

The only way to warranty a complete filling of pores is to perform a gradient PS regime formation and a first step of PRP of Ni

22



23



Cross-section made by Focus Ion Beam

Cu

Ni

Si

24



Thermal Annealing Stress of Al-p-n Ni Cu Industrial PV

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.010

-6

10-5

10-4

10-3

10-2

10-1

100

Cu

rren

t [A

/cm

2]

Voltage [V]

sample 3

as grown

300°C 1h

350°C 1h

400°C 1h

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.010

-6

10-5

10-4

10-3

10-2

10-1

100

Cu

rren

t [A

/cm

2]

Voltage [V]

sample 2

as grown

300°C 1h

350°C 1h

400°C 1h

Following Arrhenius model is possible to estimate that 100 hours at 200°C are equivalent to 4 hours at 275°C or 1 hour at 350°C. Fraunhofer Institute estimate that 100 hours at 200°C are equivalent to 100 year of normal working temperature of solar cell.

After the first two stress-annealing steps (300°C and 350°C respectively) an improvement is evident (current densities reduction in both reverse and low forward bias conditions). A further thermal annealing stress at 400°C for 1 hour destroys the junction (blue line in forward bias conditions)

25


Main results achieved: Back Side

Force [N]

Deformation [mm]

Silv

er

paste

adhesio

n t

est

F=0.5N/mm

26


Back side comparison adhesion test

Copper/Nickel/Tin plated

directly on Aluminum

Selective Plating of Cu/Ni/Sn on Al by DLD/DLM

Peel Test


27



New process developed: direct Sn plating on Al

Two steps pre-treatment in pipe-line by DLD-DLM Processing time 4s

28


BEFORE BONDING

Main results achieved

29


AFTER BONDING AND PEEL TEST: ADHESION >1.0 N/mm

Main results achieved

Different solar cell 4x4cm2 with back Ag localized contact were compared with Sn localized contact and direct Al contact

Sample Voc [mV] Jsc [mAcm-2] Normalized FF Normalized Eff Rs [cm2]

S29 - Al contact 625 36.3 1 1.000 2.3 S29 - Ag contact 586 34,6 0.782 0.700 3.0 S29 - Sn contact 624 36.1 0.992 0.992 2.3

S30 - Al contact 628 35.4 1 1.000 2.9 S30 - Ag contact 590 34.5 0.825 0.756 3.0 S30 - Sn contact 628 34.7 0.998 0.980 2.8

30


Conclusions

The New Selective Wet Processing allows:

• Plating on back contact solar cell (no need of resit)

• Plating on front contact (no need of resit)

Very fast process: Jet Plating Vfluid=2ms-1

Drag-out is very low……

• What more can DLD-DLM offer: • Edge isolation of solar cell • Wet etching (e.g. texturization of solar cells)

• And ……many other applications


Thanks for your attention

M. Balucani1,4, K. Kholostov1, P. Nenzi1, R. Crescenzi1,

L. Serenelli2, M. Izzi2, M. Tucci2

D. Bernardi3

D. Ciarniello4

1 DIET-Sapienza University of Rome, Via Eudossiana, 18 - 00184 Roma (ITALY),; 2 ENEA Casaccia Research Centre Rome, ITALY,

3 2BG S.r.l. Padova (ITALY), 4 Rise TechnolgyS.r.l. Roma (ITALY),

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New selective processing technique for solar cell