Types of Photovoltaic Cells

There are several types of photovoltaic cells. All of them are undergoing development to increase their efficiency and reduce the cost of producing them. Here's a list of the types of photovoltaic cells available.

• Monocrystalline silicon cells
• Polycrystalline silicon cells
• Amorphous silicon cells
• Cadmium Telluride cells
• Copper Indium Gallium Selenide cells

Now lets go through the list, explaining each type of photovoltaic cell.

The cell is made of a single continuous crystal lattice without boundaries and with little or no impurities in its molecular structure. These are the most efficient photovoltaic cells when operating in ideal to moderate conditions. The efficiency is about 14.5%.

Because of their relatively high efficiency, they are often employed to generate solar power where there is limited space to install the solar panels. Limited spaces like rooftops, building facades and vehicle bodies are a few examples.

Their biggest disadvantage is their relatively higher cost. The higher prices are mainly caused by the complicated and long process of producing monocrystalline silicon.

Another disadvantage of monocrystalline cells is that their efficiency rapidly drops with rising temperature of the solar panel. Also, the power output is too sensitive to changes in light intensity. This makes the cell less yielding.

If a huge leaf falls and sticks on your panel or if a huge dark cloud hides the sun, the performance of the panel may drop significantly. So panels made of monocrystalline cells are not fit to be directly connected to electrical appliances which need a relatively constant supply of power. Many systems with these cells make use of batteries which can get charged by a variable power supply and then discharge evenly.

These cells are made from silicon consisting of different kinds of monocrystalline silicon. The molecular structure of its lattice is not continous but has boundaries beween its crystals.

Polycrystalline cells are less efficient compared to monocrystalline cells but they are not super expensive to produce them. Consequently, panels made from these cells are cheaper. However, they share the same temperature coefficient with monocrystalline cells. That means their efficiency also drops with rising temperature.

Amorphous silicon is a glassy alloy of silicon and hydrogen. Hydrogen making up 10% of the alloy. The cells are in the form of thin homogeneous layers rather than crystals. This type of silicon is more tolerant to heat compared to crystalline silicon. The temperature coefficient is around 0.3%/°C.

Amorphous silicon absorbs light more effectively than crystalline silicon so cells made from it are thinner. That's why the cells are called thin-film photovoltaic cells. These cells are more yielding, meaning that they produce more solar power per power rating. They are less sensitive to changes in light intensities. This is mainly because amorphous silicon is more effective at absorbing the blue wavelengths of light that dominates during cloudy times. Crystalline cells can't do this.

And the industrial process of making amorphous silicon is relatively cheaper, making the thin-film technology cheap too. The biggest advantage of amorphous silicon comes from the fact that it's made into thin films. This makes them applicable to both rigid and foldable panels. They can also be embedded into thin glass or roof tiles. In China, there are building facades made of glass with these thin-films which are hardly noticeable when you look at the glass.

Though amorphous silicon is more yielding, it's not as efficient as crystalline silicon. The efficiency is about 6%. In an attempt to increase this efficiency, photovoltaic cell manufacturers add layers of polycrystalline silicon to the thin-film. This raises the efficiency to about 9%.

These cells came about through research in thin-film technology. Engineering scientists were looking for a more efficient and less costly alternative to amorphous silicon. That's how cadmium telluride cells emerged. There was a time when they were the cheapest but further development in silicon has put silicon ahead again.

Cadmium telluride cells have greater tolerance to heat compared to crystalline cells. But the efficiency is higher compared to amorphous silicon cells. The efficiency is around 10%. They are mainly used to make solar panels that are mounted on the ground. The kind of panels installed in huge numbers on super huge fields generating gigawatts of solar power.

These also are commercialised just like the Cadmium telluride cells. They're super cheap too just like all the other thin-films. These cells take up the biggest proportion of modules that don't use glass. This makes them light-weight and fit for applications where weight is a huge factor. Applications like roof tiles and rooftop installations are a few examples.

CIGS cells have moderate electrical properties. The efficiency is around 12% and the temperature coefficient is around -0.3%/°C.