by Steve Liker, business manager, Trident Solar
In the battle for the business of price-sensitive consumers, highly efficient photovoltaic production at reduced processing costs is key to survival. One approach that can generate significant cost savings and greater production efficiencies is use of digital inkjet printing.
Inkjet printing of contacts and bus bars has several key benefits over alternative technologies. The ability to print narrow features with small drop volume and high resolution makes it possible to minimize shadowing on the active layer. Inkjet printing can be used to dispense etchants to controllably produce undercuts or features in PV layers. This high-resolution, direct-write printing method also saves in process steps, speeds set-up time, eliminates waste, reduces cost through automation, and enables non-contact printing for thin, sensitive substrates.
Inkjet printing brings several key advantages to photovoltaic production processes. Lines or holes (50μm × 5-10μm) can be produced without the damage and defects associated with lasers. Digital printing is non-contact so breakage and resulting scrap are eliminated. In addition, inkjet can be used to jet conductive metal inks (such as silver ink) to digitally produce contact lines with thickness down to 50μm, 2×-3× finer than can be produced with silver paste, a squeegee, and screen printing — and at one-fifth the cost. This allows manufacturers to print exactly the amount of material they need exactly where they need it, saving significant time, expense, and waste. It also enhances efficiency, as contact widths can be minimized to ensure that valuable sunlight is not blocked.
Choosing the right inkjet printing system can give companies an important edge in a competitive marketplace. Not all printing systems are created equally. In order to evaluate the quality of an inkjet printing system, take a look under the hood, at the printhead. The printhead is the heart of most inkjet printing systems and its characteristics often determine the cost effectiveness and quality of the inkjet printer. Durability, print quality, and cost-effectiveness are three key elements to look for in an inkjet printhead.
|Figure 1. The printhead is the heart of most inkjet printing systems and its characteristics often determine the cost effectiveness and quality of the inkjet printer. For inkjet printing of etchants for photovoltaic cell production, an inkjet printhead with stainless steel construction can last up to eight times longer than a similar printhead of less inert material construction.|
Inkjet printing systems must be ruggedly designed to work alongside the hustle and bustle of employee and machine activity in a production environment. When producing photovoltaic contacts, very aggressive and potentially damaging materials such as acids, alkaline etchants, and conductive materials are jetted from the inkjet printhead. It is essential that an inkjet printing system be highly inert and robustly designed to provide consistent quality performance even when routinely exposed to extremely challenging materials.
Printheads typically feature orifice plates made of either metallic substances like stainless steel, or polyimide plastic films; each material provides different benefits to end-users. Plastic orifice plates are typically less expensive to produce, while stainless steel orifice plates offer greater scratch resistance, greater inertness, and increased durability.
There are other important questions to be asked about durability before purchasing an inkjet printing system:
— On average how long does the printing system run without requiring service or repair?
— Can the inkjet printhead be repaired or is it a disposable consumable?
— How many years will the printhead last before it needs to be replaced?
Carefully selecting a durable printing system for the most difficult industrial environments and the most aggressive materials can prevent costly production delays and save money on inkjet printhead components. For inkjet printing of etchants for photovoltaic cell production, an inkjet printhead with stainless steel construction can last up to eight times longer than a similar printhead of less inert material construction.
Another key factor to consider when selecting an inkjet printing system is print resolution – typically determined by the minimum drop volume capability. Precision printing of materials is important to produce the typical high tolerance features. When printing solar cell contacts it is necessary to minimize contact widths so that light is not blocked. High-resolution inkjet printing produces the narrowest possible contacts.
A third important element to study when selecting an inkjet printing system is cost. Three factors are particularly important in cost-effective printing systems: cost-per-system, jettable material cost, and printhead life/repairability.
Depending on the printable area and number of fluids dispensed, a number of inkjet printheads may be required in the manufacturing process. Fluid controls, printhead drivers and other printer system components contribute to the overall capital cost of the system.
|Figure 2. Trident’s new 256Jet-S inkjet printhead featuring a rugged, serviceable design is inert to corrosive etchant materials, offers an industry-leading lifespan and can print conductive metal contacts up to 3× higher resolution than possible with screen printing.|
In addition to being very aggressive, the jettable materials used in inkjet printing photovoltaic contacts are often expensive. Inkjet printing is an additive process, so it allows manufacturers to print exactly the amount of material they need exactly where they need it, saving significant time and expense vs. subtractive printing methods that waste valuable printing materials.
Another important factor to look for when searching for a cost-effective inkjet printing system is printhead life/reparability. When the orifice plate becomes clogged with debris, does the entire printhead need to be replaced or can it simply be repaired? A printhead with a repairable design that allows the front chamber and orifice plate to be removed, cleaned, and reassembled can save money on costly product replacements.
Finding the right inkjet printing system is key to enhancing PV production efficiency and identifying cost-saving opportunities. Taking the time to understand the technology within printing systems — especially durability, print-quality, and flexibility — is time well-invested to find the printer that is right for a particular operation.
Steve Liker is business manager at Trident Industrial Inkjet, Brookfield, CT USA; e-mail [email protected].