Multi-Layer Inkjet Printed Contacts to Si

2008 33rd IEEE Photovolatic Specialists Conference, 2008

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.

Direct-write technologies offer the potential for lowcost materials-efficient deposition of contact metallizations for photovoltaics. We report on the inkjet printing of metal organic decomposition (MOD) inks with and without nanoparticle additions. Near-bulk conductivity of printed and sprayed metal films has been achieved for Ag and Ag nanocomposites. Good adhesion and ohmic contacts with a measured contact resistance of 400 µΩ•cm 2 have been observed between the sprayed silver films and a heavily doped n-type layer of Si. Inkjet printed films show adhesion differences as a function of the process temperature and solvent. Silver lines with good adhesion and conductivity have been printed on glass with 100 µm resolution.

2003

We are developing inkjet printing as a low cost, high throughput approach to the deposition of front contacts for Si solar cells. High deposition rates of 1µm per printing pass were achieved with a new metalorganic ink composed of silver(trifluoroacetate) in ethylene glycol. The printing conditions were optimized to achieve a relatively high line resolution of 120 µm. The optimal parameters for the piezoelectric inkjet were a pulse frequency of 50 Hz and pulse amplitude of 25 V. The best resolution and the line quality were achieved at a substrate temperature of 180 °C and drop separation of 40 µm.

2002

Direct writing of solar cell components is an attractive processing approach. We have fabricated a 6.8% Si solar cell using silver ink based electrodes. Ohmic contact through the antireflection (AR) coating was obtained with pure Ag electrodes at 850 0 C. We also report on highly conductive silver metallizations and initial results on direct-write TCO demonstrating a 100micron spatial resolution produced by inkjet printing.

A review on applications of metal-based inkjet inks for printed electronics with a particular focus on inks containing metal nanoparticles, complexes and metallo-organic compounds. The review describes the preparation of such inks and obtaining conductive patterns by using various sintering methods: thermal, photonic, microwave, plasma, electrical, and chemically triggered. Various applications of metal-based inkjet inks (metallization of solar cell, RFID antennas, OLEDs, thin film transistors, electroluminescence devices) are reviewed.

1999

Our team has been investigating the use of particle-based contacts in both Si and CdTe solar cell technologies. First, in the area of contacts to Si, powders of Al and Ag prepared by an electroexplosion process have been characterized by transmission electron microscopy (TEM), TEM elemental determination X-ray spectroscopy (TEM-EDS), and TEM electron diffraction (TEM-ED). These Al and Ag particles were slurried and tested as contacts to p-and n-type silicon wafers, respectively. Linear current-voltage (I-V) was observed for Ag on n-type Si, indicative of an ohmic contact, whereas the Al on p-type Si sample was non-ideal. A wet-chemical surface treatment was performed on one Al sample and TEM-EDS indicated a substantial decrease in the O contaminant level. The treated Al on p-type Si films exhibited linear I-V after annealing. Second, in the area of contacts to CdTe, particles of Hg-Cu-Te and Sb-Te have been applied as contacts to CdTe/CdS/SnO 2 heterostructures prepared by the standard NREL protocol. First, Hg-Cu-Te and Sb-Te were prepared by a metathesis reaction. After CdCl 2 treatment and NP etch of the CdTe layer, particle contacts were applied. The Hg-Cu-Te contacted cells exhibited good electrical characteristics, with V oc > 810 mV and efficiencies > 11.5 % for most cells. Although V oc > 800 mV were observed for the Sb-Te contacted cells, efficiencies in these devices were limited to 9.1%, presumably by a large series resistance (>20 Ω) observed in all samples.

Thin Solid Films, 2014

Aerosol jet printing is a contactless deposition technique that is ideally suited to depositing features on very thin and fragile substrates such as Si wafers. It can also be used to optimize device geometries including the Al back contact of a Si wafer solar cell quickly. A printable Al ink is required for this process, and we report lines and solar cells prepared with such a material. The resistivities of the printed Al lines approach bulk after appropriate sintering. Al lines printed on Si wafers have been heated over a wide temperature range of 550 to 800°C to form low resistance contacts suitable for current extraction. Aerosol jet printed Al contacts to industrially produced 21 cm 2 polycrystalline Si solar cells performed on par with all screen printed contacts on similar cells. These promising results demonstrate the potential for non-contact printed Al to contribute to the fabrication of lowcost photovoltaic devices and modules.

VEYSEL UNSUR. Understanding the solar cell contact formation by digital inkjet printing (Under the direction of DR. ABASIFREKE EBONG)

In this paper, we report a novel approach for the fabrication of chalcopyrite CuIn x Ga 1 À x Se 2 thin film solar cells by inkjet printing. The short circuit current (J sc ), open circuit voltage (V oc ), fill factor (FF), and total area power conversion efficiency (Z) of the device are 29.78 mA/cm 2 , 386 mV, 0.44%, and 5.04%, respectively. Inkjet printing at atmospheric environment offers an opportunity for the direct patterning of absorber materials at large scale. This provides a potential cost advantage over conventional fabrication process that involves sequential deposition, patterning, and etching of selected materials. In addition, inkjet printing increases the raw material utilization ratio compared to more wasteful vacuum-based deposition techniques.

Solar Energy Materials and Solar Cells, 2011

An ink-jet method for fabrication of fine and smooth front side highly conductive silver lines on crystalline Silicon substrate is described. The fabricated conductive silver lines on different substrates are characterized by means optical microscope, optical profilometers, scanning electron microscope (SEM), and electrical measurements. The coffee-ring effect is controlled by increasing the solid loading of the ink from 20 W% to 40 W% and printing at optimum substrate temperature (90-100 1C) and optimum printing parameters. Smooth printed conductive silver lines, with line thickness ranges from 0.8 $ 0.9 mm for single pass, are obtained. When increased substrate temperature, a significant reduction of spreading of ink was observed. And conductive silver lines obtained at optimum substrate temperature (90-100 1C), free of periodic wrinkles and line bleeding, are produced. The influence of annealing temperature on line resistance, the morphology and functionality of the printed conductive silver lines is optically and electrically analyzed. To deposit thicker lines multiple passes of ink-jet printing were done on polished single crystalline silicon (sc-Si) and standard alkaline (NaOH) textured n + /p single crystalline silicon (n + /p sc-Si). Moreover, the printed conductive silver lines are characterized optically and electrically. And, promising results in terms of printed line thickness and electrical property are achieved.