PV materials firm DuPont and “silicon ink” provider Innovalight come at the selective emitter from both ends, promising improved conversion efficiencies.
July 28, 2011 – Turning a silicon substrate into a (homogenous) photoelectric device requires doping (phosphorous) to make a diode with a p-n junction. The amount of doping impacts how efficiently the cell converts energy: high doping undercuts the efficiency of converting blue light, while light doping makes it difficult for the gridlines to contact Si and carry the current out of the PV cells. Selective emitters promise the best of both worlds: heavily doping only areas directly under the silver printed gridlines where the paste can contact, but very light doping elsewhere to maximize efficiency to generate current.
It’s here that DuPont, a maker of PV materials e.g. metallization pastes (and encapsulants, etc.) and silicon ink provider Innovalight see benefits of synergies, in their M&A announced this week. The Innovalight ink formulation is screen-printed on the frontside of the wafer to create a selective emitter, and at the end of the normal cell-making process the DuPont Solamet paste is put on the same pattern over the ink, explained Rob Cockerill, business manager, DuPont Innovalight, formerly PV manager on the DuPont side. (Innovalight founder Conrad Burke will head up the new DuPont-owned unit).
DuPont’s Microcircuit Materials unit and Innovalight were already familiar with each other, having seen over the past couple of years how well their products worked in concert in forming silicon solar cells; what began as cross-promotions eventually turned into the realization that there were “lots of synergies,” noted Cockerill.
For DuPont, this is just another brick in the wall of building a growth business in solar PV. The company says it had >$1B sales to the PV market in 2010 (roughly 3% of total $31B company sales), and its goal is to double that to $2B by 2014. (assuming pledged 7% total sales CAGR, that suggests PV would rise to about 5% of total sales.) Innovalight, née a module aspirant but switched to inks & IP licensing around 2008, has publicly acknowledged about five customers in the past 12 months of early commercialization (JA Solar, Yingli, Solarfun, Jinko Solar, and Motech), but Cockerill indicated there are “many more” quiet customers “at various stages” of adoption, and claims he has received “many, many calls” since this deal went public.
Cockerill said there’s a combined up to (absolute) 1% improvement on a monocrystalline c-Si cell, with somewhat less benefit on other cells (e.g. 0.4%-0.5% for poly). For current first-gen selective emitters there’s no specific benefit to the Innovalight-Solamet combination, but he indicated that DuPont will customize its metallization pastes in the next wave of SEs: e.g., tweaking the glass chemistry to get proper etching/firing, maximizing contact and adhesion with the silicon substrate, improving printability (e.g. wafer linewidths), etc.
Last year (spring 2010) Innovalight claimed a (Fraunhofer ISE-confirmed) 19% conversion efficiency cell using its silicon ink, with a goal of 20%; DuPont has the same goal (as much as has been publically revealed, noted Cockerill) with its Solamet pastes. These overlap with what the silicon PV roadmap expects to gain with emerging architectures, e.g. back-contact, metal wrapthrough, etc, all of which can “in their own right” deliver up to 1% better efficiency, though it’s not completely additive, he said.
PV metallization technology roadmap. (Source: DuPont)
Selective emitters have been gaining ground as PV cell makers race to improve their technologies to compete with each other as well as thin-film offerings. Earlier this month the U. of New South Wales said its laser-doped selective emitters have pushed c-Si cell efficiency to 19.4% (also Fraunhofer ISE-confirmed), with eyes toward eventually reaching 22%. Earlier this year Schmid and Taiwan c-Si maker talked up a 19.2% efficient cell with a 0.6% boost from selective emitter technology.