The Thin Film Solar Cell: what is it and how does it work?The thin film solar cell is a product of Thin Film technology applied to photovoltaics. In theory thin film cells are cheaper version of the regular solar cell by virtue of the decreased amount of materials required for construction, as implied in the name. What is Thin Film Technology?Thin Film refers to the construction of a VERY thin layer of a substance on a substrate. Thin is a relative term. In comparison to the first silicon crystal solar cells produced, current thin film cells are 1% of the the thickness. Naturally these are of great interest to the solar manufacturing industry, as many more cells can be made with far less material. With single crystal or multi crystal cells the materials were up to 40% of the unit cost. Thin film technology promises to slash that dramatically.There are a variety of materials that are used in the production of thin film solar cells. Amorphous SiliconYou may have seen or heard this term in relation to commercially available solar panels. This is the oldest thin film technology and is therefore the best developed. Amorphous silicon refers to silicon atoms that can be laid down on a backing substance but do not need to be in a lattice in order to display semiconducting behaviour. This allows it to be deposited onto large areas with relative ease. Amorphous silicon does not conduct as well as cystalline silicon because the connections between the silicon atoms are not as consistent and so electron flow is more interrupted. Still, an amorphous silicon solar cell can achieve an initial efficiency of around 10%, sometimes more, so they are excellent value compared to the thick silicon wafer.DEGRADATION: A less advertised fact about amorphous silicon solar cells is that they experience a fairly rapid drop in efficiency when initially exposed to sunlight. This can be anywhere between 15 and 35%. If you are considering purchasing solar equipment that employs the amorphous silicon technology it is vital to check with the supplier whether the stated output of the device or panel is for AFTER the expected degradation or BEFORE. A decent seller would be using the after-degradation figures for electricity production. Different approaches have been taken to reduce the degradation and also improve the efficiency of amorphous silicon thin film solar cells. Using a thinner layers and stacking of layers one on another are all effective, but these processes result in higher manufacturing costs. CIGS Thin Film Technology How it Works CIGS is short for copper indium gallium selenide, which are the elements used to make the photoelectric layer in this trype of thin film solar cell. The principles behind the operation of the CIGS solar cell is the same as that of the Silicon solar energy cell. From the list of elements used in CIGS we can see that Copper acts to receive electrons, making it the same as the P-type silicon. Selenium provides extra electrons to act in the same way as the N-type silicon. These materials can be placed onto a variety of substrates including thin flexible steel, glass, and various polymers. At present the most widely used substrate is flexible steel as it is the most resistant to the high temperatures needed for the process of laying down the elements onto the backing sheet. CIGS Efficiency Rates CIGS technology is improving steadily. Current CIGS thin film solar cells with a steel backing sheet having laboratory efficiencies of up to 17%. Similar cells with a plastic backing have a lower efficiency due to the lower manufacturing temperature required. This affects the crystal formation during production. The efficiency rate of CIGS solar panels is lower than that of silicon cells but is still far greater than those of organic or plastic solar cells. Low Light Performance of Thin Film Panels Compared to a crystalline Silicon panel, an amorphous Silicon panel of comparable size produces less power but performs better at lower light intensities, making it a good low cost choice for environments where interrupted sunlight is the norm. The CIGS panel has better performance than the amorphous silicon in terms of maximum output, but worse low light performance. The CIGS panel also performs at lower overall efficiency than the standard crystalline Silicon cell. |
