Types & Efficiencies

Just a simple question: how efficient are today's solar cells? 
The answer to this question depends on several factors. High efficiency depends on a solar cell that can generate more electricity per incident solar power unit. Basically the solar cell's ability to produce more electricity in a given area. Theoretically speaking, to say that a solar cell has 100% efficiency means that the solar cell converts all of the sunlight it receives into electricity. Major solar panel manufacturers like Sharp, Q-Cell, First Solar, Kyocera Solar concentrate on improving the efficiency even by 1%. The more efficient, the more money that can be made.
The chart below shows the most efficient solar cells that has been developed and tested. Some of the high efficient solar cells have not been mass produced yet. 

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As you can see from the above graph, the most efficient that we have gotten is about 40%. This is the absolute best that is available today.  Even though it may look like it is very inefficient, it is much better than today's commercially available solar panels, which are about 15% - 22% depending on the manufacturer. These efficiencies were measured The efficiency should be measured under real conditions and the basic parameters that need to be evaluated are the short circuit current, open circuit voltage. Just for a comparison your car runs at about 30% efficiency at best!

Materials
The efficiency highly depends on the material that the solar cells are made. The most common types of solar cells are:

 

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Monocrystalline: These solar panels are made from a large crystal of silicon. These type of solar panels are the most efficient as in absorbing sunlight and converting it into electricity, however they are the most expensive. None the less, these are becoming more and more popular. Efficiency: 18% - 22%

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Polycrystalline: These solar panels are the most common type of solar panels on the market today. They look a lot like shattered glass put together in a frame. They are slightly less efficient than the monocrystalline solar panels and less expensive to produce. Instead of one large crystal, this type of solar panel consists of multiple amounts of smaller silicon crystals. Efficiency: 15% - 18%

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Amorphous (thin film): This type of solar panels consist of a thin-like film made from molten silicon that is spread directly across large plates of stainless steel or similar material. These types of solar panels have lower efficiency then the other two types of solar panels, and the cheapest to produce. Average Efficiency: 10%

It is interesting to see all the other types of materials that are being tested today....

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Fun Fact: According to Encyclopedia Britannica the first genuine solar cell was built around 1883 by Charles Fritts, who used junctions formed by coating selenium (a semiconductor) with an extremely thin layer of gold.