Online information source for semiconductor professionals

Many corporate newsletters offer little more than an informercial-like experience, with so-called technical or market information that often comes off like a frozen-smiled, pat-oneself-on-the-back excuse for real content. But can you honestly expect something from a company's corporate communications cabal to provide the objective quality and unshakeable editorial integrity of something like, say, this blog or the publication website on which it is published? A site, btw, which would not have the financial means to exist if not for the advertising monies that some of those same companies spend to reach the eyeballs of the most important constituency--the visitor-reader? But I digest....

There are exceptions (Soitec's Advanced Substrate News comes to mind), so when a newsletter arrived in my inbox yesterday that does transcend, at least a little bit, the typical self-serving fare, I took notice. The source is Advanced Energy, and the quarterly publication in question is PV Sun Times, sent to the power supply, gas/chemical flow control, and instrumentation system company's solar manufacturing contacts. (AE also issues newsletters with flat panel and sputter focuses--to receive any of them, you need to register on the company's site.)

AE's PV communique leads off with a technical brief on how the proper set-up of multiple RF electrodes in solar-cell-on-glass PECVD batch systems can lead to improved throughput. Although the solution offered leads to the inevitable call to try out the company's subsystems and to contact its apps engineers, the main part of the article does offer a decent overview of the problem of electrode crosstalk and stray plasma encountered in this process.

My favorite part of the newsletter is the "Ask the Solar Experts" column, which poses questions to AE's Doug Pelleymounter and Ken Nauman and their collective 45 years of experience in the solar PV field. I'm not sure whether the questions are staged or legit queries from customers, but the virtual banter has a down-home yet technically grounded feel that is informative even if it's a tad corny.

The opening questions are admittedly very AE-centric, asking what the company "brings to the table for PV manufacturing" and then, in the case of an inquirer allegedly "just starting out" and needing to "order a large volume of equipment at once," whether AE can "provide all the equipment I need within a tight timeframe." Doug and Ken's short answers are that the company "has one of the most comprehensive product lines in the industry" (for its kinds of gear) and that its prodigious Shenzhen, China, factory can handle orders of 30 MW or larger and AE can support its customers anywhere in the world.

In the second answer, I liked the experts' folksy explanation of how the company's years of working in the semiconductor, flat-panel, and other industries benefits/complements its PV business: "One nice thing for the emerging solar market is that it can take advantage of all the development that has happened for existing, adjacent markets." It's always a nice thing when one tech can borrow and learn from another, without those dreaded "reinventing the wheel" scenarios.

The feature's third and fourth questions dive deeper into production issues. The first of the final two asks why someone should choose vacuum-based manufacturing and what advantages it holds over evaporation and printing techniques, and the final query (coming from the copper-indium-gallium-[di]selenide [CIGS] thin-film PV sector), wonders about how to control the temperature of a transparent or thermal conductive oxide (TCO) process to "avoid degrading the active layer underneath it."

Rather than paraphrase the experts' answers, here are excerpts of what they had to say. I've excised most of the more egregious commercial passages (though not all), and what remains are, to my eye, solid summary nuggets that would fit well in an introductory primer on the subjects under discussion.

"Today's methods for PV manufacturing include sputtering (PVD), PECVD, printing, evaporation, and more. However, vacuum-based processes such as PVD and PECVD offer definite benefits that the other methods simply can't deliver. Specifically, PVD and PECVD provide atomic-level control that enables you to more precisely control film characteristics, such as stoichiometry, crystallinity, and uniformity across the substrate. PVD and PECVD also produce fewer defects than other methods. This high level of control culminates in two critical benefits for today's solar panel manufacturers: greater PV efficiency and increased throughput....

"Another benefit of using a vacuum-based process is the fact that within the areas of PVD and PECVD, a great deal of expertise and technological development has been amassed that can be applied directly to PV manufacturing. [Blogger's Note: Now brace for commercial impact...] AE offers over 25 years of experience, as well as a comprehensive and highly developed product portfolio that enables an exceptional level of control over film properties compared to other subsystem manufacturers. For example, our products enable a lower defect rate, which not only increases solar cell efficiency, but allows higher-power operation as well, resulting in increased throughput. Higher-power operation also enables successful coating of large-area substrates....

Here's an excerpt of Doug and Ken's reply to the CIGS question.

"Thermal budgeting is a pressing issue for many manufacturing applications today. A little background for our readers: most PV manufacturing processes deposit the TCO layer first, before any other layers. However, for CIGS (and some thin-film Si) solar cells, the TCO is the last to go down. Unlike metal layers, which can be deposited with cold processes because their electrical conductivity is relatively unaffected by temperature, the conductivity of TCOs is highly affected by heat.

"To produce sufficient conductivity, conventional TCO processes are performed at high temperatures. The problem is that for CIGS processes, which deposit the TCO last, this may exceed the thermal budget of all preceding layers. Excessive temperature can cause diffusion of the dopant within the active layers underneath the TCO, resulting in significant PV performance degradation. Further, if the substrate is temperature-sensitive, it can actually melt under the temperatures of conventional TCO deposition processes. This is a particular issue for flexible polymer substrates....

"....Power methods exist that can be performed in a temperature range that will not cause diffusion of the active layers or substrate melting, while producing good TCO conductivity. These are standard methods with records of success for other processes requiring temperature control, such as for electrodes for FPD color filters, and transparent conductors for touch panel processes...."

Kudos to Advanced Energy for putting a few more photons of useful info in its 'mercials.