The only remaining piece of the puzzle is the catalyst that starts this transfer of "free" electrons

Figure 1: P-N Junction6
http://docs.google.com/File?id=dfd49hhc_12ffjw9gcg_b6 REUK. Renewable energy UK. Retrieved October, 2008, from http://www.reuk.co.uk/OtherImages/pnjunction.jpg
7 Aldous, S. How solar cells work. Retrieved October, 2008, from http://www.howstuffworks.com/solar-cell.htm
The only remaining piece of the puzzle is the catalyst that starts this transfer of "free" electrons to the "holes" on the other side. This process is called the photovoltaic effect. The photovoltaic effect describes the interaction between a photon, a particle of light, and specific metal materials. When a photon interacts with a metal material it may be reflected or absorbed. If absorbed, the photon transfers its energy to a local atom, which in turn, lends its energy to an orbiting valence electron. This process causes a free electron which is capable of moving to a "hole" creating an electrical current. The more photons that interact with the material, the more valence electrons are freed and allowed to flow to an electron-hole. Once light is absorbed by the two materials, electricity begins to flow through the connected load. The more light that interacts with the solar cell, the more electricity is generated.7

Figure 2: Solar Panel Construction and Implementation8 On a bright, sunny day, the sun shines with approximately 1 kilowatt of energy per square meter on the Earth's surface. To gather this energy solar panels are generally coated with a non-reflective surface texture. This texture increases the probability that a photon will be absorbed rather than reflected. A cross section of composition can be seen below.
http://docs.google.com/File?id=dfd49hhc_11hn4x2ddc_b8 The Seitch Blog. Retrieved October, 2008, from www.blog.thesietch.org/wp-content/uploads/2007/06/solarcell.jpg

Figure 3: Solar Cell Composition
2.2.3 Different Types of Photovoltaic Panels
Crystalline Silicon (Traditional Method)
The largest and most popular solar panel technology on the market today is commonly referred to as crystalline silicon solar cells. Being one of the original solar panel technologies it is not surprising that this type of solar panel currently holds an unprecedented 93% of the market to date. Because of its relatively simple construction and manufacturing process, crystalline solar cells gained large popularity during the infancy of the alternative energy boom.
Today, there are two major types of crystalline silicon used in manufacturing and production: mono-crystalline and poly-crystalline. The first, mono-crystalline, requires absolutely pure semi-conduction material. Melted silicon is first poured in the shape of rods. After a solid has formed, the rods are then sawed into thin small wafers which are up to 150 mm in diameter and 350 microns thick. This type of production results in an approximately 24% lab efficiency, and 15% efficiency in production.9
Solar Panel Layers.bmp9 The Solarserver. (2008). Photovoltaics. Retrieved October, 2008, from http://www.solarserver.de/wissen/photovoltaik-e.html

Figure 4: Mono-Crystalline Solar Cells
The second type of crystalline silicon chiefly used today is referred to as poly-crystalline. Poly-crystalline production is similar to mono-crystalline in the way that both result in silicon wafers, however, the method by which the final product is created differs. First, liquid silicon is poured into blocks that are then cut into bars, and then finally cut into wafers. Because the silicon hardens in large blocks, many large crystalline structures begin to form, hence “poly-crystalline”. Poly-crystalline cells are more cost effective to produce due to the fact that many cells can be created from a single block, but because every time silicon is cut, the edges become deformed, which results in a lower operating efficiency. The efficiency for a poly-crystalline cell in the laboratory is approximately 18% and in production reaches only 14%.10
10 The Solarserver. (2008). Photovoltaics. Retrieved October, 2008, from http://www.solarserver.de/wissen/photovoltaik-e.html

Figure 5: Poly-Crystalline Solar Cells
The benefits of a crystalline solar cell come from the fact that the cells that comprise the overall solar panel are very cheap to produce. Because crystalline cells were one of the first technologies on the scene, much of the production and manufacturing techniques have been refined to their maximum potential. Despite effective production processes, one of the largest problems that plague crystalline silicon cells is the limits of their efficiency. When any crystalline structure is split it undergoes deformation. The technique by which mono-crystalline and poly-crystalline cells are created intensely relies on severing of silicon into smaller pieces. This leaves much of the area deformed which decreases operating efficiency for that cell. This is one of the reasons that String Ribbon technology (which is covered in the next section) is so efficient, because it manufactures silicon in a method that produces no deformities.
String Ribbon Panels
With the ever increasing demand of cheap solar panel production techniques, it has become critical for companies to devise new alternatives for producing silicon. One of the most promising of these techniques is String Ribbon manufacturing. Unlike the generic silicon wafers used in the bulk of solar panel production today, string ribbon provides a healthy alternative which decreases production costs as well as the carbon footprint used to produce a solar cell. The technique behind String Ribbon silicon is the manipulation of surface tension. Two parallel strings are pulled vertically through a silicon melt. As the strings rise, silicon begins to span the distance between the two strings, much like a bubble spans the ring on which it is blown. As the silicon rises it begins to cool and form a hardened structure between the strings. This process continues uninterrupted until the silicon ribbon is of desired length.11
11 SolarHome.org. (2008). String-Ribbon. Retrieved October, 2008, from http://www.solarhome.org/string-ribbon.html