by Pete Singer, editor-in-chief, Solid State Technology
Oct. 15, 2008 - Albuquerque, NM-based Advent Solar is bringing advanced semiconductor technology to the PV industry. Using epi-filled through silicon vias (TSVs) and the equivalent of wafer-level packaging, the company has developed a new approach that enables a back contact approach that reduces 3%-4% loss in efficiency from front-side conductors. They also claim lower cell processing and interconnect costs compared to other backside contact technologies.
Company execs were at Solar Power International this week in San Diego, in advance of the first product launch planned for the first quarter of next year and manufacturing beginning mid-year. Peter Green, president and CEO, said the first two years of worth of production were already sold. He declined to state specific efficiencies, preferring to wait until the official announcement in 1Q09, but said he believes that company's technology will allow them to get to grid parity, "as fast or faster than the best technology out there now."
The company was founded in 2002 based on patents developed at Sandia, including a emitter wrap through (EWT). That has since evolved into what is called a MMA (monolithic module assembly). The manufacturing process begins with a patterned cell size copper sheet; an insulation layer is deposited, followed by pick-and-place of the solar cells. "The throughput is much faster and we're able to use thinner silicon," said Martin Hermann, chief strategic officer. He said they've demonstrated the feasibility of working down to 120μm thick wafers, but that the industry is presently at 200μm, moving to 180μm. He also said the pick-and-place ability helps reduce silicon breakage, which is typically 2%-3% of the silicon in conventional PV processes.
Naresh Baliga, VP of strategic marketing, added that the approach also leads to greater manufacturing precision. He noted that variations in conventional stringer/tabber approaches for interconnects can create "large bin splits" (using the vernacular of the semi industry) which may create a loss of 4% in efficiency. "You might be shooting for a 200W module and you wind up with 170W," he said.
Grids take up 8% of area, and that leads to a problem -- as efficiency increases (technology advances and/or the use of concentrators), so does the amount of power than must be transported, which can tax existing technology. "You can't get the power out due to limitations of wires," Green said. And increasing conductance by increasing the size of the lines leads to reduced efficiency. By comparison, the Advent Solar approach -- which they call "Ventura Technology" -- has "indefinite" conductivity since most of the backside is a conducting copper sheet. -- P.S.