National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337 

T. Kaydanova, M.F.A.M. van Hest, A. Miedaner, 

C.J. Curtis, J.L. Alleman, M.S. Dabney, 

E. Garnett, S. Shaheen, and D. Ginley 

National Renewable Energy Laboratory

L. Smith and R. Collins 

Colorado School of Mines 

J.I. Hanoka and A.M. Gabor 

Evergreen Solar, Inc. 

Prepared for the 31st IEEE Photovoltaics Specialists 

Conference and Exhibition 

Lake Buena Vista, Florida 

January 3–7, 2005

February 2005 • NREL/CP-520-37524 

Direct Write Contacts for 

Solar Cells
NOTICE 

The submitted manuscript has been offered by an employee of the Midwest Research Institute (MRI), a 

contractor of the US Government under Contract No. DE-AC36-99GO10337. Accordingly, the US 

Government and MRI retain a nonexclusive royalty-free license to publish or reproduce the published 

form of this contribution, or allow others to do so, for US Government purposes. 

This report was prepared as an account of work sponsored by an agency of the United States

government. Neither the United States government nor any agency thereof, nor any of their employees, 

makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, 

completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents 

that its use would not infringe privately owned rights. Reference herein to any specific commercial 

product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily 

constitute or imply its endorsement, recommendation, or favoring by the United States government or any 

agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect 

those of the United States government or any agency thereof. 

Available electronically at http://www.osti.gov/bridge

Available for a processing fee to U.S. Department of Energy 

and its contractors, in paper, from: 

U.S. Department of Energy

Office of Scientific and Technical Information 

P.O. Box 62

Oak Ridge, TN 37831-0062

phone: 865.576.8401 

fax: 865.576.5728 

email: mailto:reports@adonis.osti.gov

Available for sale to the public, in paper, from: 

U.S. Department of Commerce 

National Technical Information Service

5285 Port Royal Road 

Springfield, VA 22161 

phone: 800.553.6847 

fax: 703.605.6900 

email: orders@ntis.fedworld.gov

online ordering: http://www.ntis.gov/ordering.htm

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste 
Direct Write Contacts for Solar Cells 

Tanya Kaydanova1, Maikel F.A.M van Hest1, Alex Miedaner1, Calvin J. Curtis1, Jeff L. Alleman1, Matthew S. 

Dabney1

, Eric Garnett1, Sean Shaheen1,Lee Smith2, Reubin Collins2, Jack I. Hanoka3, Andrew M. Gabor3 

and David S. Ginley

1 

1

National Renewable Energy Laboratory, 1617 Cole Blvd., Golden Colorado 80401 USA 2

Colorado School of Mines, Golden Colorado 80401 USA, 3

Evergreen Solar, Inc., 259 Cedar Hill Street, Marlboro, MA 01752 USA 

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 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 850oC resulting in 8% cells. 

Next generation multicomponent inks (including etching 

agents) have also been developed with improved fire 

through contacts leading to higher cell efficiencies. 

PEDOT-PSS polymer based conductors were inkjet 

printed with conductivity as good or better than that of 

spin-coated films. 

INTRODUCTION 

Inkjet printing is rapidly becoming a viable alternative 

to the existing deposition approaches for a variety of 

inorganic and organic electronic materials[1]. For 

metallizations with appropriate inks, it can replace vacuum 

deposition, screen printing and electroplating. 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 easily

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

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 printer set up is pictured on Fig. 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. 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. 

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. 

1 
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 shown 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 inkjetprinted contacts produced to date is presented in Table 1.

Typical conductivities for the metallic coatings were: 

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

for Ni. The conductivity 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 

(μ.cm) 

Printing 

temperatur

e (o

C) 

Ag(1) 1- 15 100-

250 

2 200

Ag(2) 1- 15 300-

600 

7 250

Cu 1-15 200-

300 

10 250

Ni 4 100 250

PEDOT:

PSS 

0.1 300 700 50-75

Firethrough 

agent 

1-5 70-

200 

NA 200

(1) – Ag from metalorganic ink developed at NREL 

(2) – Ag from frit-containing nanoparticle ink (Ferro) 

INKJET-PRINTED SILVER GRIDS ON CRYSTALLINE 

SILICON SOLAR CELLS

Pure Ag grids 

250 μm wide, 10 μm thick Ag lines were inkjet-printed 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. 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 

burning 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 two 

independent directions described below. 

Grids from glass containing silver inks. 

Glass-frit containing inks analogous to screen-printed 

pastes in composition but with nanosized Ag particles 

were supplied by Ferro. The small particle size of the Ag 

powders used in these inks make them suitable for inkjet 

printing with the 50μm jet. They were successfully printed 

resulting in 15μm thick, 500μm wide lines (Figure 4). 

 

Fig. 4. 100x microscope image of the 15μm thick, 500μm 

wide Ag lines inkjet printed from Ferro’s frit-containing ink 

 

Using these inks, ohmic contacts were achieved at much 

lower temperatures (650o

C, 750oC) with a very short 

annealing cycle (less than a minute). Further optimization 

of the ink composition and printing processes is underway. 

Pure Ag grids with etching underlayer 

 

Simultaneously we explored another approach to reduced

times and temperatures for processing inkjet-printed silver 

contacts. 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 

2 
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. Fig. 5 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. 

 

Fig. 5. AFM image of the 1μm deep, 70μm wide etch 

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

on an AR coated Si wafer 

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 Ferro’s 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, but the lack of good control of the 

time-at-temperature has limited these cells to modest 

efficiencies. Optimization of the annealing process is 

underway and should result in improved efficiencies. 

INKJET-PRINTED PEDOT-PSS CONTACT FOR 

ORGANIC SOLAR CELLS 

Organic solar cells and organic optoelectronics rely in

many cases on thin films of PEDOT as an organic TCO.

We report on an extension of the inkjet printing process to 

high performance PEDOT lines and films. 

An aqueous suspension of PEDOT/PSS (Baytron P 

HCV2) was obtained from Bayer. It was printed both asreceived and diluted with water or ethyl alcohol, and with

additives such as dimethyl sulfoxide (DMSO) and 

surfactant (Surfynol 2502 from Air Products) in order to 

achieve highly conducting and smooth PEDOT-PSS films 

and patterns. Uniform PEDOT lines as narrow as 300μm 

were inkjet printed on glass substrates (Fig. 6). 

Fig. 6. 50x microscope image of the 300 μm wide PEDOT

line inkjet printed on ITO 

Continuous films were produced by printing

overlapping adjacent lines. The distance between the 

printed lines was varied for each ink composition in order 

to achieve smooth films. It was found that film roughness, 

thickness and conductivity were controlled by various 

parameters including type of solvent, dopant, substrate 

temperature and the settings of the inkjet. The smoothest 

films were achieved by printing at 50o

C. The inkjet-printed

films were consistently more conducting than films spincoated from the same ink (Table 2). 

Table 2 – Inkjet-printed versus spin-coated films 

Sample description Thickness 

(nm) 

Roughness 

(nm) 

Conductivity

(S/cm) 

Inkjet Printed PEDOT 350 24 4.3

Spin-coated PEDOT 160 2.5 3.1

Inkjet - 1:1 

PEDOT/water 

150 24 4.7

Spincoat – 1:1 

PEDOT/water 

60 2.5 3.7

Inkjet – 1:1 

PEDOT/water +5% 

DMSO 

300 33

Inkjet – 1:1 

PEDOT/water + 5% 

DMSO +1% Surfynol 

300 40 51

Inkjet – 1:1 

PEDOT/water + 1% 

DMSO +1% Surfynol 

180 35 31

The increased conductivity of the inkjet versus spincoated films is not entirely understood, but may be due to 

preferential polymer alignment or orientation that occurs 

with longer drying time. The best conductivity of 51 S/cm 

was achieved by adding 5 wt% DMSO and 1% Surfynol. 

The increase of conductivity with DMSO has been 

previously demonstrated for spin-coated films [4, 5]. The 

3 
surfactant Surfynol was added to the ink to improve the 

wetting properties of the polymer for smoother films. 

However, it not only produced visibly more uniform and 

smoother films, but it also increased the conductivity by a 

factor of about 1.5, which has not been observed before. 

Finally it was found that the value of the workfunction (by 

CPD) for the inkjet-printed polymer could be varied by as 

much as 0.5V by various additives. This is instrumental for 

matching the workfunctions of the PEDOT-PSS layer with 

other layers in the device. 

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

1 Solvents

CPD (V)

Spincoated (water)

water

water w/o O2 plasma pretreatment

water/EtOH

water/EtOH + 5% DMSO

water/EtOH + 5% DMSO w/o O2 plasma

pretreatment

ethanol + 5% DMSO + 1% Surfynol w/o O2 plasma

pretreatment

water + 5% DMSO

water + 1% Surfynol 2502

water + 5% DMSO + 1% Surfynol 2502

Fig. 7 – Contact Potential Difference (CPD) of PEDOT

films printed under identical conditions with various 

solvents and substrate pretreatments. 

CONCLUSIONS 

In summary, we have developed atmospheric direct-write 

deposition of metals including Ag, Cu and Ni. Line widths, 

conductivities and thicknesses are comparable to or better 

than those produced by screen printing. We have shown 

how new inks can improve the contacting process for Si 

photovoltaics. We have demonstrated inkjet printed 

patterns of highly conductive PEDOT polymer for contacts 

in organic photovoltaic cells. Future work will focus on 

improved resolution, multicomponent/multifunctional inks 

for enhanced contacts and improved inks for better 

conductivities of Cu and Ni metallizations. 

REFERENCES 

[1] D. B. Wallace, W. R. Cox, and D. J. Hayes, DirectWirte Technologies for Rapid Prototyping Applications, p. 

177.: Academic Press, 2002.

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

Schulz and D. S. Ginley, "Copper and silver inks for inkjet 

printing.," presented at 198 th International Symposium of 

the Electrochemical Sosciety, Phoenix, Arizona, 2000. 

[3] C. C. T. Rivkin, A. Miedaner, J. Perkins, J. Alleman, 

and D. Ginley, "Direct Write Processing for Photovoltaic 

Cells," presented at IEEE 29th Photovoltaics Specialists 

Conference, New Orleans, Louisiana, 2002. 

[4] S. K. M. Jonsson, J. Birgerson, X. Crispin, G. 

Greczynski, W. Osikowicz, A. W. D. van der Gon, W. R.

Salaneck, and M. Fahlman, "The effects of solvents on the 

morphology and sheet resistance in poly (3,4-

ethylenedioxythiophene)-polystyrenesulfonic acid 

(PEDOT-PSS) films," Synthetic Metals, vol. 139, pp. 1-10, 

2003. 

[5] J. Y. Kim, J. H. Jung, D. E. Lee, and J. Joo, 

"Enhancement of electrical conductivity of poly(3,4-

ethylenedioxythiophene)/poly(4-styrenesulfonate) by a 

change of solvents," Synthetic Metals, vol. 126, pp. 311-

316, 2002. 

4 
F1147-E(12/2004) 

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, 

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this 

collection of information, including suggestions for reducing the burden, to Department of Defense, Executive Services and Communications Directorate (0704-0188). Respondents 

should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a 

currently valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

February 2005 

2. REPORT TYPE

Conference Paper 

3. DATES COVERED (From - To)

3-7 January 2005 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Direct Write Contacts for Solar Cells 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/CP-520-37524 

5e. TASK NUMBER

PVA54201 

6. AUTHOR(S) 

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

J.L. Alleman, M.S. Dabney, E. Garnett, S. Shaheen, L. Smith, 

R. Collins, J.I. Hanoka, A.M. Gabor, and D.S. Ginley 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

NREL/CP-520-37524 

10. SPONSOR/MONITOR'S ACRONYM(S)

NREL 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

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

demonstrating good adhesion to glass, Si, and 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 antireflective layer at 850o

C resulting in 

8%-efficient cells. Next-generation multicomponent inks (including etching agents) have also been developed with 

improved fire-through contacts leading to higher cell efficiencies. PEDOT-PSS polymer-based conductors were 

inkjet-printed with conductivity as good or better than that of spin-coated films. 

15. SUBJECT TERMS

PV; direct wire contacts; solar cells; inkjet printing; multicomponent inks; polymer-based conductors; spin-coated 

films; 

16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified

c. THIS PAGE 

Unclassified

17. LIMITATION 

OF ABSTRACT

UL 

18. NUMBER 

OF PAGES 

19b. TELEPHONE NUMBER (Include area code)

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18