Reel-to-reel reaction of a precursor film to form solar cell absorber

A method of reacting precursor material disposed over a continuous workpiece, the continuous workpiece being formed in a sheet that is continuously fed comprising:

• feeding at a predetermined rate range a substantial length of the sheet of the continuous workpiece through a process gap that is leak-free;
• heating each portion of the substantial length of the sheet of the continuous workpiece in a first zone of the process gap maintained at substantially a first temperature range;
• heating each portion of the substantial length of the sheet of the continuous workpiece in a second zone of the process gap maintained at substantially a second temperature range, wherein the second temperature range is higher than the first temperature range;
• and
• passing each portion of the substantial length of the sheet of the continuous workpiece through a first buffer zone of the process gap that connects the first zone to the second zone, wherein the predetermined rate range causes each portion of the substantial length to be disposed within the first buffer zone for a period that is less than 10% of another period that each portion is disposed within the second zone, wherein the buffer zone includes cavities of low thermal conductivity that together significantly inhibit transfer of thermal energy from the second zone to the first zone while still maintaining the process gap, including the buffer zone, leak-free.

An apparatus used to continuously feed portions of a continuous workpiece with a front surface and a back surface through the apparatus to react a precursor layer disposed over the front surface of the continuous workpiece to form a solar cell absorber, comprising:

• a rapid thermal processing tool, the rapid thermal tool including a continuous and leak-free process gap through which the continuous workpiece travels, the process gap having a top wall, a bottom wall and side walls such that there exists an aspect ratio of 1/50 to 1/1000 between its height and width;
• a moving mechanism to move the continuous workpiece through the process gap while keeping the back surface of the continuous workpiece in physical contact with the bottom wall while keeping a distance between the precursor layer and the top wall;
• wherein the process gap further includes:
• a top cold region with a first temperature range, a top buffer region, and a top hot region with a second temperature range associated with the top wall, such that the top buffer region is between the top cold region and the top hot region;
• a bottom cold region, a bottom buffer region, and a bottom hot region associated with the bottom wall, such that the bottom buffer region is between the bottom cold region and the bottom hot region, so that a section of the continuous workpiece is subjected to a third temperature range as the section of the continuous workpiece travels over the bottom cold region and a fourth temperature range as the section of the continuous workpiece travels over the bottom hot region, and wherein the fourth temperature range is higher than the third temperature range;
• and
• wherein the top buffer region and the bottom buffer region each includes a plurality of cavities within each of the top wall and the bottom wall that provide low thermal conductivity areas that together significantly inhibit transfer of thermal energy from the top hot region to the top cold region and from the bottom hot region to the bottom cold region, respectively, while still maintaining the process gap leak-free.