National Renewable Energy Laboratory 

Innovation for Our Energy Future 

A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 

Multi-Layer Inkjet Printed 

Contacts for Silicon Solar Cells 

Preprint 

C.J. Curtis, M. van Hest, A. Miedaner, 

T. Kaydanova, L. Smith, and D.S. Ginley 

Presented at the 2006 IEEE 4th World Conference on 

Photovoltaic Energy Conversion (WCPEC-4) 

Waikoloa, Hawaii 

May 7–12, 2006 

Conference Paper 

NREL/CP-520-39902 

May 2006 
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MULTI-LAYER INKJET PRINTED CONTACTS FOR SILICON SOLAR CELLS*

Calvin J. Curtis, Maikel van Hest, Alex Miedaner, Tanya Kaydanova, Lee Smith, and David S. Ginley 

National Renewable Energy Laboratory, Golden, CO 80401 

ABSTRACT 

Ag, Cu, and Ni metallizations were inkjet printed with 

near vacuum deposition quality. The approach developed 

can be easily extended to other conductors such as Pt, 

Pd, Au, etc. Thick highly conducting lines of Ag and Cu 

demonstrating good adhesion to glass, Si, and printed 

circuit board (PCB) have been printed at 100-200o

C in air 

and N2 respectively. Ag grids were inkjet-printed on Si 

solar cells and fired through the silicon nitride AR layer at 

850o

C, resulting in 8% cells. Next generation inks, 

including an ink that etches silicon nitride, have now been 

developed. Multi-layer inkjet printing of the etching ink 

followed by Ag ink produced contacts under milder 

conditions and gave solar cells with efficiencies as high as 

12%. 

INTRODUCTION 

Inkjet printing is rapidly becoming a viable alternative 

to the existing deposition approaches for a variety of 

inorganic and organic electronic materials[1]. With 

appropriate inks, it can replace vacuum deposition, screen 

printing and electroplating for depositing metallizations. 

The advantage of inkjet printing is that it is an atmospheric 

process capable of resolution higher than in screenprinting (features as small as 5μm have been produced 

using an inkjet). It is a non-contact, potentially 3D 

deposition approach, which makes it ideally suited to 

processing thin and fragile substrates. The composition of 

the inks may be easily tailored by the addition of elements 

such as adhesion promoters and doping compounds to 

optimize mechanical and electronic properties of the 

subsequently processed contact. In addition, inkjet printing 

is inherently suited for printing multilayer/multicomponent 

structures. We report here on ink-based approaches to 

printing Ag, Cu and Ni metallizations with near vacuum 

deposition quality. This approach can by analogy be 

extended to other conductors such as Pd, Pt and Au. 

INKJET-PRINTED METALS 

Organometalic compounds of Ag, Cu and Ni in 

organic solvents (proprietary compositions) were used as 

the precursor inks for inkjet and spray printing of the 

metallic layers and patterns. When spray-printed with an 

airbrush on heated glass substrates at 200-250o

C in air, 

the metal precursor inks fully decomposed forming 

metallic coatings without detectable traces of carbon[2] or 

oxides (Fig. 1). 

8000

6000

4000

2000

0

Intensity (cps)

35 40 45 50 55°

2 Theta (degrees)

100

80

60

40

20

0

1 1 1

2 0 0

1 1 1

2 0 0

1 1 1

2 0 0

 Printed Ag layer on glass

 Printed Cu layer on glass

 Printed Ni layer on glass T Standard Ag T Standard Cu T Standard Ni

Fig 1. X-ray diffraction patterns of the spray-printed 

organometallic precursor inks. 

The inkjet printing apparatus is pictured on Figure 2. It 

consists of a stationary drop-on-demand piezoelectric 

inkjet head from Microfab Technologies with a 50-micron 

orifice. A resistive substrate heater plate positioned on an 

X-Y stage directly under the inkjet serves to provide 

heating and x-y positioning to 1 μm. The printing 

parameters and patterns were controlled by computer 

using LabView. Printing parameters such as substrate 

temperature and translation speed, as well as the inkjet 

driving parameters, the frequency and amplitude of the 

controlling voltage pulses, were optimized to achieve the 

best resolution and highest conductivity for Ag and Cu 

metals. 

Fig. 2. Inkjet printhead positioned over a glass substrate. 

*This work has been authored by an employee or employees of the Midwest Research Institute under Contract No. DE-AC36-99GO10337 with the U.S. 

Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United 

States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others 

to do so, for United States Government purposes.

1
Thick (up to 15μm), highly conducting lines of Ag and Cu 

were printed on a variety of substrates, demonstrating 

good adhesion to glass, Si and PCB (Figure 3a,b). The 

inkjet parameters for Ni printing have not yet been 

optimized. 

In general, we found that the best Cu deposits were 

obtained in an inert atmosphere (N2 or Ar). However, pure 

Cu coatings, including the one characterized in Fig. 1, 

were obtained in air using rapid thermal processing. 

 

 a b 

Fig 3. (a) 300μm wide, 5-μm thick Cu lines printed on PCB 

in N2 at 200o

C. (b) 250μm wide, 10μm thick Ag grids 

inkjet-printed on a Si solar cell in air at 200o

C. 

A summary of the important characteristics of the 

inkjet-printed contacts produced to date is presented in 

Table 1. Typical resistivities for the metallic coatings were: 

2μOhm*cm for Ag, 10μOhm*cm for Cu and 100 μOhm*cm 

for Ni. The resistivity of the Ag layer is essentially that of 

the bulk metal, the Cu and spray-printed Ni layers 

demonstrate approximately an order of magnitude higher 

resistivity than the bulk values. Improving conductivity of 

printed Cu and Ni metallizations is an area of active 

investigation. 

Table1. Important Characteristics of Printed Conductor 

Patterns 

Material Thick 

ness 

(μm) 

Linewidth 

(μm) 

Resistivity 

(μΩ⋅cm) 

Printing 

temperature 

(

o

C) 

Ag 1- 15 100-250 2 200 

Cu 1-15 200-300 10 250 

Ni 4 100 250 

Firethrough 

agent 

1-5 70-200 NA 200 

INKJET-PRINTED SILVER GRIDS ON CRYSTALLINE 

SILICON SOLAR CELLS

Pure Ag grids 

Ag lines 250 μm wide and 10 μm thick were inkjetprinted on silicon nitride coated Si ribbon p/n junctions 

provided by Evergreen Solar, Inc. 1μm thick Al back 

contacts were deposited by e-beam evaporation. The two 

contacts were co-fired in a single annealing step at 850o

C 

for 10 min in air, forming a solar cell with 8% efficiency, 

Voc=0.529V, Jsc= 22.67mA and a fill factor of 0.65 (Figure 

3b). In this experiment, the ohmic contact between Ag and 

Si was formed through the SiNx layer without the use of 

glass frits to enhance etching. The high temperature and 

long time required for the penetration of the Ag through 

the AR coating[3] can be detrimental for the junction. 

Facilitating the process of etching through the AR coating 

is desirable to lower the temperature and time of 

annealing for the inkjet-printed contacts. In order to 

achieve this goal, we explored printable etching agents 

and multi-component inks. 

Table 2 summarizes the processing and performance 

for Si cells with inkjet printed contact grids. The first 

generation is the cell just described, the second 

generation used Ag ink modified for better line width, and 

the third used the etching under layer described below. 

Table 2. Summary of line dimensions, processing 

temperatures and efficiencies for Si cells with inkjet printed 

contacts. 

Generation 1st 2nd 3rd

Line thickness 10 μm 15 μm 15 μm 

Line width 400 μm 250 μm 220 μm 

Deposition 

temp 

180°C 180°C 180°C 

Annealing 

temp 

850°C 850°C 750°C 

Efficiency 8% 8% 10% 

Pure Ag grids with etching underlayer 

 

A significant advantage of inkjet printing is that it 

allows multi-layer printing, so that separate writing of the 

contact formation layer and then the metal forming layer is 

possible, leading to more control of the contact formation 

process and improved conductivity of the conductor lines. 

Next generation multicomponent inks (including 

surface modifying agents) have been developed to obtain 

improved fire-through contacts. These proprietary inks 

greatly improve the burn through and contact formation 

process. Figure 4 depicts a 1μm deep, 70μm wide etch 

pattern obtained by inkjet printing an ink containing a 

proprietary etching agent on a SiNx coated Si substrate, 

followed by thermal processing at 750o

C for 10 min. 

Complete penetration of the SiNx layer was observed at 

temperatures as low as 500o

C. 

Experimental solar cells have now been fabricated 

using this process. These cells were formed by sequential 

printing of the etching agent layer followed by the 

deposition of the Ag lines from organometallic precursors 

as described above. Back contacts were screen-printed 

using Al paste. However, annealing of the structure has 

proven to be more difficult than anticipated. Short (40 sec) 

anneals at 550°C in our lamp RTP furnace have yielded 

poor results due to non-uniform overheating and 

penetration of the contact layer too deep into the Si 

substrate. Short anneals in a conventional furnace have 

given better results (Table 1, 3rd generation), but the lack 

of good control of the time-at-temperature has limited the 

2
performance of these cells. However, cell efficiencies as 

high as 12% have now been observed. Further 

development of the ink composition and optimization of 

the annealing process are underway and should result in 

improved efficiencies. 

Fig. 4. AFM image of the 1μm deep, 70μm wide etch 

pattern produced by the inkjet-printed “fire-through” agent 

on an AR coated Si wafer 

CONCLUSIONS 

An atmospheric, direct-write deposition technique has 

been developed for metals including Ag, Cu, and Ni. Line 

widths, conductivities and thicknesses are comparable to 

or better than those produced by screen printing. It has 

also been demonstrated that new inks and multi-layer 

printing can improve the contacting process for Si 

photovoltaics and lead to better cell performance. 

Future work will focus on improved resolution, 

multicomponent/multifunctional inks for enhanced contacts 

and improved inks for better conductivities of Cu and Ni 

metallizations. 

ACKNOWLEDGEMENTS 

This work is supported under DOE Contract No. DEAC36-99GO10337. 

REFERENCES 

1. Wallace, D.B., W.R. Cox, and D.J. Hayes, DirectWrite Technologies for Rapid Prototyping 

Applications. 2002, New York: Academic Press. 

177. 

2. T. Rivkin, C.J.C., A. Miedaner, J. Alleman, D. L. 

Schulz and D. S. Ginley. Copper and silver inks 

for inkjet printing. in 198 th International 

Symposium of the Electrochemical Sosciety. 

2000. Phoenix, Arizona: The Electochemical 

Society, Inc. 

3. T. Rivkin, C.C., A. Miedaner, J. Perkins, J. 

Alleman, and D. Ginley. Direct Write Processing 

for Photovoltaic Cells. in IEEE 29th Photovoltaics 

Specialists Conference. 2002. New Orleans, 

Louisiana: IEEE. 

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