What Is A Solar Cell (Photovoltaic Cell)

Bell Laboratory scientists are believed to have discovered photovoltaic cells in 1954. Successful use of photovoltaic cells (PV cells) in US space programs in the late 1950s generated tremendous commercial interest in this technology. Since then there has never been a looking back for this new technology of solar cells.

Their use in calculators, wristwatches is almost taken for granted now. Many remote and inaccessible areas of the world are using electricity generated by the solar cells (PV cells) as the only available energy source to run water pumps, communication equipments and domestic or even community lighting.

Use of solar electricity for homes is catching up and PV generated electricity for co-generation in large power houses is also gaining wider acceptance.

• Structure of a Solar cell and Solar panels

Majority of the solar cells in common use are based on the use of a metal Silicon processed in such a manner as to exhibit strong photovoltaic properties converting visible solar radiation into electricity. Some other materials have also been developed and new manufacturing technologies are developed to increase conversion efficiency, to reduce cost, convenience of use, etc – and developments will go on.

Without getting into technical details, let us understand what a photovoltaic cell is made of and how it operates. As we mentioned earlier, Silicon metal, refined to a great extent and processed in a particular manner, is used to make a solar cell which converts solar radiation falling on the device and generates electricity. But Silicon is a very shiny material and the sunrays falling on it may get reflected away and would hardly contribute towards generating electricity. So a solar cell (PV cell) incorporates some antireflective material to help the conversion process. Figure 1 alongside shows the basic construction of a photovoltaic cell.

As shown here, a solar cell uses two wafers of Silicon processed in different manners, so that their “sandwich” has the capacity to convert energy from sun’s rays into electricity. Of course, this “sandwich’ must have contacts on both sides to collect electricity produced, an antireflective coating has to be incorporated and a transparent physical protective layer of glass must be incorporated. Well, there is your solar cell!

For many practical reasons, a single cell cannot be very large and can give hardly 1 or 2 watts of power. For practical purposes a number of PV cells are assembled in a panel and interconnected in series/parallel combinations so that sufficient electricity can be generated by using them. For large output a number of such panels are assembled together in an array as shown in figure 2; arrays are large, rigid structure.

Before going further, we must once again stress that there are various new techniques, processes and materials being used now to produce PV cells. We mention only a few variations here as an illustration.

• Single-crystal cells are made in long cylinders and sliced into round or hexagonal wafers. This process is rather wasteful and uses a lot of power but produces solar cells giving efficiency of up to 25%. A fairly large proportion of present day photovoltaic cells are of this type;


• A process similar to that used in production of rolled steel sheets is also used; this results in what is called the polycrystalline cells. Solar cells produced in this manner are reasonably low in cost but, on the downside, their efficiency is rather poor- about 15%. These cells can be packed together more closely in making solar panels. Well over 50% of the global use of solar cells is of this type;


• A process in which silicon is essentially sprayed on to glass or metal surface in thin films produces what is called as amorphous silicon photovoltaic cell. Amorphous-silicon solar cells are the cheapest – unfortunately they are the least efficient also – hardly 5%.