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Innovation for Our Energy Future 

Direct-Write Contacts: 

Metallization and Contact 

Formation 

Preprint 

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

R.M. Pasquarelli, T. Kaydanova, P. Hersh, 

and D.S. Ginley 

National Renewable Energy Laboratory

Presented at the 33rd IEEE Photovoltaic Specialists Conference 

San Diego, California 

May 11–16, 2008 

Conference Paper 

NREL/CP-520-42535 

May 2008 

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DIRECT-WRITE CONTACTS: 

METALLIZATION AND CONTACT FORMATION

Maikel F.A.M. van Hest, Calvin J. Curtis, Alex Miedaner, Robert M. Pasquarelli, Tanya Kaydanova, 

Peter Hersh, and David S. Ginley 

National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401 USA 

ABSTRACT 

Using direct-write approaches in photovoltaics 

for metallization and contact formation can significantly 

reduce the cost per watt of producing photovoltaic 

devices. Inks have been developed for various 

materials, such as Ag, Cu, Ni and Al, which can be used 

to inkjet print metallizations for various kinds of 

photovoltaic devices. Use of these inks results in 

metallization with resistivities close to those of bulk 

materials. By means of inkjet printing a metallization grid 

can be printed with better resolution, i.e. smaller lines, 

than screen-printing. Also inks have been developed to 

deposit transparent conductive oxide films by means of 

ultrasonic spraying. 

INTRODUCTION 

 In an effort to reduce the cost and improve 

efficiency of photovoltaics, alternatives to conventional 

processing techniques are becoming a necessity. One 

of the most attractive alternative approaches is the 

application of direct-write approaches for depositing 

contact metallization. Using inkjet printing as the directwrite technique has multiple benefits over the currently 

used screen-printing or photolithographic techniques. 

The first benefit is that inkjet printing is a non-contact 

technique. As wafer and ribbon Si cells get thinner this 

is especially attractive allowing higher process yield. 

This is also potentially useful for textured or thin films on 

plastics where conformal coating is difficult by contact 

methods. The second benefit of using inkjet printing is 

that the resolution of the contact grid lines can be 

improved compared to screen-printing. Where typical 

line widths for screen printing are around 100 μm, line 

widths using inkjet printing can be reduced to less than 

50 μm, which significantly reduces the shadow losses 

by the contact grid and therefore increasing the overall 

cell efficiency. 

APPROACH 

Multiple inks have been developed that can be 

used to inkjet print metal grids. Silver, copper, nickel, 

and aluminum metal organic decomposition (MOD) inks 

have been developed that will form pure metal at low 

temperature (<200oC) with near bulk conductivity [1,2]. 

A modified Fujifilm-Dimatix material printer (see fig. 1) 

has been used to deposit line patterns. For initial testing 

of ink an ultrasonic spray system is used to print uniform 

films (see fig. 1). 

Fig. 1: Fujifilm-Dimatix Materials Printer (top), inkjet 

head and ink cartridge (center) and ultrasonic spray 

nozzle (bottom). 

1
 Ultrasonic spraying can also be used to deposit 

large area contacts, such as back contacts. Metal grid 

patterns are printed on a hot substrate in order to obtain 

the best conductivity. Printing on a hot substrate 

(T<200oC) has the benefit of not needing a secondary 

anneal step in order to obtain pure and conductive 

material [3]. This is for example suitable for contact to 

TCOs and organic photovoltaics directly. 

RESULTS 

Metalization 

 Fig. 2 shows the line dimensions for printed silver 

and nickel as a function of the number of layers printed. 

It can be seen that the line width is almost independent 

of the number of layers, therefore making it very easy to 

thicken the material to the desired thickness. In this 

example the line width for nickel and silver are 80 μm 

and 110 μm respectively. 

Fig. 2: Line width, thickness (top) and resistivity (bottom) 

as function of the number of layers printed using the 

nickel (A) and silver (B) inks. 

Also it can be seen in Fig. 2 that the thickness 

increases continuously with the number of layers. Even 

though in the shown example that the thickness per 

pass is of the order of 50 nm increasing the MOD 

precursor loading concentration in the ink and 

decreasing the drop spacing can increase this number 

to about 1μm per pass. By optimizing the printing 

conditions the line width can be significantly reduced to 

our currently best of around 30-40 μm (see fig. 3). This 

number can be improved even more by changing the 

nozzle diameter on the inkjet system. This however 

would reduce the line thickness per pass due to a 

reduction in droplet diameter and volume. 

The resistivity of the lines as function of the 

number of passes is also shown in fig. 2. It can be seen 

that for silver a resistivity of 3x10-6 Ωcm is obtained, 

which is close to that of bulk silver (1.6x10-6 Ωcm). 

Optimizing the printing conditions has obtained 

resistivity as low as 2x10-6 Ωcm for silver. The resistivity 

of inkjet printed silver lines is significantly better than 

that of screen printed silver lines, which are typically in 

the range of 5 to 10 times bulk resistivity. In the case of 

printed nickel the resistivity does not reach number as 

close to bulk as for silver. This is most likely due to the 

formation of small amounts of nickel oxide. Using the 

nickel ink in an inert environment will likely reduce the 

resistivity significantly. 

Fig. 3: Micrograph images of inkjet printed silver lines 

using a metal-organic decomposition precursor. Lines 

and individual drops printed on SiNx-coated ribbon 

silicon. 

Screen-printing pastes contain frit material that 

facilitates the burn-through process of the printed grid 

lines through the silicon nitride anti-reflection coating 

typically present on top of a silicon photovoltaic device. 

An ink to replace this frit material has been developed 

that can be printed in between the silicon nitride and the 

silver grid lines (see fig. 4) to facilitate burn-through. 

This ink will etch through the silicon nitride at relatively 

low temperatures (<750oC). Using the burn-through ink 

in combination with the silver ink has produced siliconbased cells with efficiencies similar to or better than 

those produced using conventional screen-printed 

contacts. The best contact resistance for inkjet printed 

contacts using inkjet printed burn-through material and 

inkjet printed silver was found to be 7 mΩcm2

 which is 

below that of screen-printed contacts. Using the burnthrough layer approach also reduces the amount of 

2
silver that is needed since the inkjet printed silver has 

better conductivity than the screen-printed alternative. 

Fig. 4: Schematic of using a separate burn-through 

material in combination with pure silver to produce 

contacts for silicon photovoltaic devices with SiNx antireflection coating. 

Printed contacts are nor limited to siliconbased photovoltaics, but they can also be used for 

contacts to CuInSe2 and organic thin film photovoltaic 

devices. Also it should be possible to replace silver with 

a less costly material such as copper. If copper is used 

for metallization on silicon photovoltaic devices a buffer 

layer of some kind needs to be introduced to prevent 

copper from diffusion into the silicon, which would 

negatively affect the efficiency. A candidate buffer 

material would be nickel. Changing metallization 

material from silver to a cheaper material would 

contribute to a reduction in production cost of 

photovoltaic devices. 

Transparent Conductive Oxides 

Another field for which inks have been 

developed are the deposition of transparent conductive 

oxides (TCOs). TCO layers are used in thin film 

photovoltaic devices, such as CIGS, CdTe and organic 

photovoltaics. TCOs are also used in heterojunction 

wafer silicon devices and as an alternative to the SiNx

anti-reflection coating. The later has the potential to 

reduce the number of grid lines and therefore reducing 

the shadow loses on a device. Using a non-vacuum 

technique for the deposition of TCOs will contribute to a 

reduction in production cost. Inks have been developed 

for a variety of TCOs, e.g. amorphous indium zinc oxide 

and doped zinc oxides. Initial testing is underway and 

the results are very promising. Conductivities 

comparable to vacuum deposition processes can be 

obtained [4,5]. 

CONCLUSIONS 

Using direct-write approaches in photovoltaics 

for metallization and contact formation can significantly 

reduce the cost per watt of producing photovoltaic 

devices. This is accomplished in two ways. First the 

direct write deposition techniques can be used under 

atmospheric conditions, which eliminates the need of 

costly vacuum deposition techniques. Second better 

resolution in comparison to screen-printing can be 

obtained, resulting in higher efficiency devices. 

This work was supported by the U.S. 

Department of Energy under Contract No. DE-AC36-

99GO10337 with the National Renewable Energy 

Laboratory. 

REFERENCES 

[1] T. Rivkin, C.J. Curtis., A. Miedaner, J. Alleman, D. L. 

Schulz and D. S. Ginley, “Copper and silver inks for 

inkjet printing.”, 198th International Symposium of the 

Electrochemical Society., 2000. 

[2] T. Rivkin, C.J. Curtis., A. Miedaner, J. Perkins, J. 

Alleman, and D.S. Ginley, “Direct Write Processing 

for Photovoltaic Cells.”, IEEE 29th Photovoltaics 

Specialists Conference. 2002

[3] A.L. Dearden, P. J. Smith,, D.-Y. Shin, N. Reis, and 

P. O’Brein, “A Low Curing Temperature Silver Ink for 

Use in Ink-Jet Printing and Subsequent Production of 

Conductive Tracks”, Macromol. Rapid Commun, 2005, 

26, pp. 315-318 

[4] G.G. Choi, S.-J. Seo, and B.-S. Bae, “SolutionProcessed Indium-Zinc-Oxide Transparent Thin-Film 

Transistors”, Electrochem. Solid State Lett., 2008, 11

pp. H7-H9 

[5] M.L. de la Olvera, H, Gomez, and A. Maldonado, 

“Doping, vacuum annealing, and thickness effect on the 

physical properties of zinc oxide films deposited by 

spray pyrolysis”, Solar Energy Mater. and Solar Cells, 

2007, 91, pp. 1449-1453 

3
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Direct-Write Contacts: Metallization and Contact Formation; Preprint

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M.F.A.M. van Hest, C.J. Curtis, A. Miedaner, R.M. Pasquarelli, 

T. Kaydanova, P. Hersh, and D.S. Ginley 

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14. ABSTRACT (Maximum 200 Words)

Using direct-write approaches in photovoltaics for metallization and contact formation can significantly reduce the 

cost per watt of producing photovoltaic devices. Inks have been developed for various materials, such as Ag, Cu, Ni 

and Al, which can be used to inkjet print metallizations for various kinds of photovoltaic devices. Use of these inks 

results in metallization with resistivities close to those of bulk materials. By means of inkjet printing a metallization 

grid can be printed with better resolution, i.e. smaller lines, than screen-printing. Also inks have been developed to 

deposit transparent conductive oxide films by means of ultrasonic spraying. 

15. SUBJECT TERMS

PV; direct-wire contact; inkjet printing; transparent conductive oxide; ultrasonic spraying; metal organic 

decomposition; metallization 

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