Making Own Solar Cell? Part 1: Processing of Silicon

There are a few questions from the many visitors who unfortunately have not had time to author a response. Many ways and forms of the question, but the core is all mawon sami. The first question related to the possibility of making or assembling their own solar cells or independently. While the second question is about the use of raw materials for solar cells made more specifically for the type of silicon solar cells which currently rule the solar cell market. Well, this article will explore two questions little by way of merging the two questions above in two separate articles; can we make solar cells made from independently with natural materials around?

The author believed the sweet promises and wonderful dreams teklnologi offered by solar cells to provide electricity in the long term have been invited even thinking intention to develop their own solar cells in the homeland. Physical form of solar cells that look very simple, easy to install and fairly easy to carry, easy to invite the assumption solar cells. Then, after knowing that the basic material of silicon solar cells authentic type of sand or soil is silica which many have encountered in our homeland, growing more common assumption that the solar cells is likely be developed in a clear ground water will be enough business aroma stung in the future.

A fellow visitors of this blog to write a question like the one below. Authors take this question as a sample of some previous similar questions and preparing this article the author to explain what and how the processing of silicon from silica sand, as well as deciding whether the production of silicon for solar cells we can do or not.

Eric said:
September 12, 2008 at 5:16 pm

Salam kenal Pak Adhi ..

I am interested to produce mono or poly crystalline silica krital. considering in this country there are lots of silica sand but still not optimally use. My question is, whether to convert from natural silica to poly / mono-crystal requires complicated processes? And what kira2 requisite investment costs ..

Thank you ..

There are a lot of silicon in the earth. He is the second largest element in the Earth's crust after oxygen. There are in nature in the form of silica sand or quartz degan also known by the chemical formula SiO2. Land where we pijak also contains silicon. For example, in Indonesia penamnangan silica sand was carried out in Central Kalimantan and Central Java. On the south coast of Java is also believed to have the silica sand deposits. Silicon used for semiconductors and solar cells taken from the separation of Si and O. Currently, the largest silicon producer in the world is China, America, Brazil, Norway and France. Silica resource reserves and the availability of electricity is large enough to be the reason why the countries in the lead in producing silicon.

It takes great power.

The first stage begins with the manufacture of silicon silicon separating the road from the SiO2. The separation is done in a furnace (furnace) is supplied with high-powered electricity. Scheme for the separation of silicon furnaces can be seen below.

Figure 1. Scheme of separation / manufacture of silicon from silica sand. Adapted from here.

Silica sand and carbon (C) simultaneously (picture at left) is inserted into the furnace is equipped with electrodes where the electric current flowing in (middle picture). Silicon separated by silica sand reacting with carbon at high temperatures, ie above 1900 up to 2100 degrees Celsius. This is considering both sand and carbon are two solids in which the reaction takes place only when they melt / melt / melt, coupled with melting point of silica sand over 1800 degrees Celsius. (The chemical reaction is not included).

The high temperature separation process of silicon from silica sand with high consequences of absolute power consumption is used. Why must the electricity and not by burning? Any combustion will not be able to reach the required temperature process for treating silica sand with carbon, so the only way a large flow of electricity aurs is an ideal process temperature can be achieved.

Recorded about 10 to 30 MW (megawatts) of electricity needed in this process depends on how much the furnace is used. Not surprisingly, the only countries which have abundant resources and electricity comes from nuclear power plants or other who may be economically separate the silicon from silica sand because electricity is needed in this process is very large; approximately one-tenth of the electricity produced by the Muara Karang power plant (300 MW) out just for this process.

Figure 2. Muara Karang power plant. One-tenth of its capacity of 300 MW is needed to separate the silicon from silica sand.

Silicon resulting from the separation of Si and O in the silica sand should be purified back to achieve purity silicon levels above 99%. There are two stages to purify the silicon result silica sand separation. The first stage, silicon still has a separation of "impurity" in the form of iron (Fe), aluminum (Al), calcium (Ca) and titanium (Ti) and carbon (C) to be issued. Done at this stage purification process just after the molten silicon out of the furnace (Fig. left center). This process involves the oxidative gas is conducted at a temperature of 1700 degrees Celsius. Large electric power is still needed in this phase. Until this stage, the resulting silicon is called the Metallurgical grade silicon with impurity levels in units of parts per million (ppm, parts per million) are true enough to be used for many purposes.

The next stage, is the preparation and purification of the raw material silicon for solar cells and semiconductor or semiconductor-called grade silicon. This stage is done in other places apart from the separation process of silicon. For information, silicon for semiconductors require purity levels are very high that different from Metallurgical grade silicon. In the world of semiconductors, known as the "nine-eleven" or 11 number 9 which states the level of purity silicon in percent; 99.999999999%. Silicon for the semiconductor must have an element of impurity in units of parts per billion (ppb, parts per billion) or parts per setrilyun (ppt, parts per trillion). Quite simply, if the silicon purity levels below the nominal value, can be guaranteed that a computer processor or memory or solar cells can not walk very well.

Purification of silicon for solar cells and other semiconductors made in the form of gas through a process called the Siemens process. Silicon from the first purification step (Metallurgical grade silicon) reacted with hydrochloric acid gas (HCl) to make silicon chloride gas. This reaction process carried out at a temperature of 350 degrees Celsius.

Silicon chloride and then inserted into the reactor Siemens (picture below), together with hydrogen gas. In the Siemens reactor are the bait rod silicon (silicon feed rod) inverted U-shaped heated at a temperature of 1100 degrees Celsius and cooling. Silicon chloride having a decomposition reaction or a decomposition reaction on the surface of a silicon-silicon bait rod, and silicon results are attached to and unraveling terendap in these bars. The longer the process, the more silicon that settles that enlarges into silicon with a purity level of 11 number 9 on the (chemical reaction is not included).

Figure 3. Schematic diagram of the process and the Siemens reactor for purifying silicon. Adapted from here.

To this end, silicon has a purity that can be used for the purposes of solar cells.

Silicon for solar cells

Solar cells made from silicon in the form of a flat square with a size of 5 x 5 cm or 10 x 10 cm square. The thickness of silicon is about 2 mm. Flat square slab called a silicon wafer for solar cells. Form of silicon wafer solar cells is different from silicon wafers to other semiconductor (chip, computer processor, RAM memory) is a flat round despite having the same thickness (see figure below).

Figure 4. Silicon wafers for electronics (round and flat) and solar cells (blue squares).

This silicon wafer is made through the silicon wafer manufacturing process using high purity silicon-yield previously (semiconductor grade silicon). In summary, the authors describe several ways to make silicon wafers for solar cells.

1. Monokristal type silicon wafer.

Mono crystalline silicon here means it is composed of a single crystal only. While other types of silicon wafers are polycrystals consisting of many krstal. Monokristal silicon wafer is made through a process of Czochralski (CZ) which is the heart of the silicon wafer manufacturing process for semiconductors as well. The process involves the fusion semiconductor grade silicon, followed by income bait rod in the molten silicon into silicon. When the bait rod is withdrawn slowly from the molten silicon, it will automatically be molten silicon from the trunk mennempel bait and frozen as a single large crystal silicon. Temperatures ranged from the 1000-1200 degrees Celsius, the temperature at which silicon can be melted / melting / melted. Silicon which had been frozen was eventually cut into pieces to produce wafers with a thickness of about 2 millimeters.

Figure 5. Scheme Cz process to make silicon wafers. (Top) reactor where the wafer manufacturing slikon, (Middle top) state tengat silicon rod pulled by the feeder. Note the color of the fluorescent signal silicon is still in a state of semi-liquid / melt. (Middle bottom) Room silicon wafer manufacturing plant that is always maintained clean and uniform workers who always used. (Bottom) The resulting silicon wafer (diameter 20-40 cm in length can reach 1-2 m). Adapted from here and here and here.

Figure 6. Solar cells using silicon base material monokristal. Consider a homogeneous blue color on the solar cells.

2. Polycrystals type silicon wafer.

Monokristal silicon wafer is relatively far more difficult and more expensive. Monokristal silicon is used for base material in semiconductor microchip, processor, transistor, memory and so on. State monokristal (containing only one single crystal) makes silicon monokristal almost flawless and very good levels of electricity and heat conductivity. Solar cells will work very well with a high level of efficiency when using this type of silicon.

However, keep in mind that the big issue is how the solar cells to reduce prices still far from the reach of the community. Use clear silicone will monokristal price melonjakkan solar cells that eventually it kontraprduktif. Industry and research community solar cells eventually turn into another type of silicon that is cheaper, easier to make, though somewhat less sacrificing efficiency levels. Currently, both the silicon and polycrystals monokristal same as used by the public.