Thin Film Solar Cell – Getting More Power Out of Semiconductor Materials

Summary: Thin film solar cells use much less semi-conductor material than crystalline solar cells.

You might have heard about Thin Film Solar Cells. What indeed are they? Why are they called “thin film”? And what advantages do these have over conventional solar cells?

Most times, when we talk about solar cells, we are referring to what are called crystalline solar cells.

A typical crystalline solar cell is made from silicon contains a active semiconductor material layer that is about 300-micrometers (micrometer is a millionth of a meter) thick. For a thin film solar cell, the equivalent is about 10 micrometer.

That is, a thin film cell uses just about 3% of the semiconductor material that a crystalline solar cell does.

Thin film solar cells come in much higher variety than crystalline solar cells. While crystalline solar cells are mainly made from silicon, thin film solar cells today could be made from Silicon (called the amorphous silicon or a-Si solar cells), Cadmium Telluride (called the CdTe solar cells), Copper Indium Gallium Selenide (CIGS) or Copper Indium Selenide (CIS).

While thin film solar cells on average have efficiencies lower than those for crystalline cells (average efficiencies of 12% for thin film vs 17-18% for crystalline cells), thin film solar cells offer some advantages in terms of

  • Flexibility,
  • Ability to perform better at high temperatures, and
  • Ability to perform well at low sunlight

Cost-wise, thin film solar cells cost slightly lower than crystalline solar cells for the same capacity, as of 2014.

Thin film solar cells are so called because they contain a much thinner layer of semiconductor material than crystalline solar cells.

Questions from the curious cat

By how much do thin film solar cells contain lesser material than crystalline solar cells?

In some cases, thin film solar cells contain less than 3% of the semiconductor material that crystalline solar cells contain.

What is the highest efficiency reached for thin film solar cells?

As of mid 2014, the highest efficiency shown by thin film solar cells in real life solar farms has been about 16%

Are all thin film solar cells flexible?

Not necessarily. Some thin film solar cells, especially those used in large scale solar farms, are sandwiched between glass. These hence are rigid solar cells.

However, many thin film solar cells have more flexible substrates, such as polymers, and in these cases, the thin films solar cells are quite flexible.

Can thin film solar cells be used in building integrated photovoltaics?

Yes, thin film solar cells are ideally suited for building integrated photovoltaics (BIPV), where the solar cells are required to cover large portions of the building, sometimes even including windows and other structures with diverse shapes. In these cases, it will very difficult, if not impossible to use crystalline solar cells – thin film solar cells, especially those with flexible substrates, lend themselves well to these BIPV applications.

How much do thin film solar cells cost?

As of 2014, per W, thin film solar panels cost almost the same as crystalline solar panels. The cost is in the range of $ 60-70 cents per W. Up to about 2012, thin films were costing much less per W than crystalline solar cells; however, with the steep reductions in the price of polysilicon (the starting material for crystalline solar cells), the price gap between crystalline and thin film solar cells has narrowed significantly.

Can thin film solar cells last 25 years in difficult environments?

Good question. Testing done by thin film cell makers in labs and other simulations show that these have the durability to withstand harsh climatic and other environment conditions for 25 years.

That said however, as of 2014, there are few, if any instances of thin film installations anywhere in the world that have been around for over 15 years. So, we do not really have any empirical proof.

Is the manufacturing process for thin films different from those for crystalline solar cells?

Yes. The thin film solar cell manufacturing process has fewer steps than the process for crystalline solar cells.

The manufacturing process starts by depositing the thin semiconductor film on the substrate, either glass or a transparent film. In the next stage, in a single step process, the film is structured into cells and a solar module. Unlike crystalline modules, the manufacturing process of thin-film modules is a continuous, single process with fewer steps.

Some interesting videos for you

A nice post on thin film solar cells in general and the different layers in a Cadmium Telluride solar cell