This is a new method of manufacturing thin multi-crystalline Silicon photovoltaic cells.
The method involves a centrifuge that is able to run efficiently at the melting point of silicon.
The size of the centrifuge is about 12" in diameter and approximately 15" in length. It spins at fairly low speeds on a horizontal axis. The centrifuge is heated from the inside with a moveable carbon based heater. It runs in a near vacuum. A carbon 'boat' measuring about 1.1" wide x 13" long by about 0.010" thick with part of the middle of the strip milled out to a depth of about 0.007". Some molten Silicon is deposited into the 'cavity' where it immediately hardened and grip the carbon strip tightly. The Si/C strip is loaded into slots in the inner portion of the outer skin of the centrifuge. Then a vacuum is drawn and the heat and rotation is turned on. The silicon melts and due to the centrifugal force, the surface tension is broken and the silicon spreads over the milled out surface of the carbon. Due to the low temperature, no SiC is formed at the interface. The heating element is withdrawn and crystal growth proceeds lengthwise resulting in fairly large single crystal grains. Then the temperature is lowered quickly and the vacuum is released. The silicon /carbon strip is shuttled into a phosphorus diffusion chamber where the junction is formed. Then the edges of the silicon carbon strip is machined off so that the junction is not shorted out. Then, collector strips are deposited onto the top surface and the carbon acts as the bottom collector.
The advantage of this system is as follows: There is no saw loss of silicon. (That loss is about 50%) The amount of silicon in a cell is about 0.004"-0.006", which is about 1/2 the normal amount. The energy required is about 20% of normal. The cells themselves are very robust versus easily breakable like todays conventionally made silicon cells.
Eliminating sawing and grinding of silicon cuts the time of manufacture substantially.
Also, the absence of breakage will be substantial.
Submitted by Larry Kelley, Shelby, MI, USA
http://www.createthefuturecontest.com
