All About Thin-Film Photovoltaic Cells (TFPV)
Source: researchgate.net

All About Thin-Film Photovoltaic Cells (TFPV)

The year was 1972 – Solar Power Corporation just saw the light of the day. And then, the year 1973 saw the birth of the Solarex Corporation and the first photovoltaic system for domestic purposes got the green light at the University of Delaware. These found usage in several types of equipment such as medical equipment, telecommunication, refrigerators, etc. 

With several improvements over the years, technology has massively improved and has started gaining massive traction over the last few years. With the focus on shifting to renewable energy more vigorous than ever, we see no reason for its growth to slow down.

In this article, we discuss the basics of thin-film photovoltaic cells (TFPV).

What is the photovoltaic effect?

In layman terms, the photovoltaic effect refers to energy produced by two dissimilar materials when exposed to light or similar power. The electrons are not in a free movement state within a crystal (generally silicon), but the exposure to a radiant source helps some of them gain the ability to move. 

These then start settling on one side, giving it a negative charge, and eventually creates negative voltage concerning the other side. It is known as the photovoltaic effect, and it continues until the radiant energy falls on the pane.

What is a thin-film photovoltaic (TFPV) cell? 

Thin-film photovoltaic (TFPV) cells are an upgraded version of the 1st Gen solar cells, incorporating multiple thin PV layers in the mix instead of the single one in its predecessor. These layers are around 300 times more delicate compared to a standard silicon panel and are also known as a thin-film solar cell.

These employ the photovoltaic effect to convert the sun’s energy into an electrical one. Depending on the variant, its thickness can range between few nanometers to few micrometers. 

TFPV cells vs monocrystalline cells

  • The panels made out of a single crystal of pure silicon are known as the monocrystalline cell
  • TFPV cells are flexible and lighter than their monocrystalline counterparts.
  • Mono cells hit back by offering higher efficiency due to their inherent structure.
  • Mono cells are also better than TFPV panels by up to 10 per cent in high-temperature conditions.
  • Monocrystalline panels are a better choice when space is a constraint.
  • Most premium mono panels last up to 50 years, with 25 years of them or so covered in the warranty. TFPV cells are newer in the market and usually come with 20 years of lifespan. 

Thin-film solar panels price per watt 

In the last decade, the cost of solar panels has fallen by around 90 percent while the deployments increased by a massive 400 percent. Calculating the solar panel price per watt (PPW) is an essential consideration while deciding if the investment in them is worth it or not. 

There are two parameters that you will need to calculate that efficiently. The first element is the Gross System Cost (GSC), which is inclusive of all the costs incurred. The second one is the System Size (SS), which can be reached by multiplying Panel DC Watts with Number of Panels. Dividing the GSC by SS will give you the applicable PPW. If it ranges between $0.5-$1.00, the investment is worth it.

Types of thin-film photovoltaic cells

Silicon solar panels

Silicon solar cells (also known as organic photovoltaic cells) utilise organic polymers or small organic molecules to produce and store electricity. These can sustain several design languages or are left utterly transparent due to their ability to use various observers organically. Silicon solar cells use multiple layers of solution between electrodes to help it conduct energy.

The energy storing levels are similar to CdTe, and ongoing research is looking for ways to improve it. The organic photovoltaic cells suffer from higher degradation rate than other inorganic modules, making it a costlier option in the long run.

New thin-film technology 

Amorphous silicon

Amorphous silicon cells are made of silicon but follow a different method than poly or mono panels. They require a substrate like metal, glass, or plastic for construction. A non-crystalline silicon solution is deposited on it, and it lets the user choose the width of the panel.

Amorphous panels use a lower quantity of silicon compared to other thin-film photovoltaic solar cells. These are more flexible too but suffer from lower efficiency also. They have an efficiency rate of 7 percent compared to 14 to 20 percent of polycrystalline or monocrystalline.

Cadmium telluride (CdTe)

The cadmium telluride (CdTe) solar cells come second in popularity after the amorphous panels. These include several layers where one is the main energy-producing layer made from CdTe, and the rest are for electricity conduction and collection. These find preference because they can capture shorter wavelengths and convert them to energy, which most other silicon panels are incapable of, making them optimal for electricity conversion.

They, unfortunately, suffer from high pollution generation. It is not harmful to human beings when they are actively using it, but cadmium being a highly toxic material is a risky affair when it comes to disposal. For efficiency, they offer higher retention than amorphous panels but are not as good as standard silicon panels.

CIGS (Copper Gallium Indium Diselenide)

Similar to other thin-film photovoltaic cells, the CIGS panels depend on substrates. A compound called copper gallium diselenide is deposited between multiple conductive layers, and all of it is spread on glass, aluminium, steel, or plastic. Depending on the substrate, the final product may vary in terms of flexibility.

CIGS is amongst the panels with the highest efficiency, with the ability to store more than 20 percent. But one issue that it suffers from is the presence of high levels of cadmium, which makes disposal a herculean task. Thankfully, some newer models are replacing it with zinc altogether. 

Gallium arsenide (GaAs)

Mostly used in spacecraft and satellites, gallium arsenide cells are highly efficient, reaching up to 30 percent in laboratory conditions. These are composed of two elements – gallium and arsenide, which bind to conduct electricity and trap it. These are highly costly to produce, which has deterred people from using it for general purposes, but scientists found out some ways to manufacture them at a cheaper cost.

Similar to most other TFPV cells, these are not easily disposable. Even though gallium is a non-toxic material, its partner-in-crime, arsenic is a common toxic element and also a carcinogen, making it difficult to break down in natural conditions.

Applications of thin-film solar cell

The first recorded application of thin-film photovoltaic cells dates back to the 1980s when they were common in watches and calculators. Thin films can operate efficiently in weak lighting conditions. Also, they are more consistent when the temperatures are soaring. Here are some of their typical applications that you are likely to come across – 

  • Thin-film photovoltaic panels are an appropriate choice for solar farms.
  • You can also install them in street lights and traffic signals.
  • Users can also install these in large rooftops, forest areas, commercial buildings, and similar infrastructure spread over a large area.
  • Installing thin-film photovoltaic cells over buses can help you regulate its temperature.
  • They can also aid water tanks in pumping out water.
  • If you do not have a large area to spare, you can install limited cells for powering appliances that require little energy to run. 

Advantages of thin-film photovoltaic cells

  • These allow users to add solar energy generating capacity to complex structures where you cannot install the conventional silicon panels.
  • They are lighter than full-fledged panels and offer higher flexibility.
  • These are easier to install and manage.
  • These are apt for wide-open landscapes or large rooftops.
  • These are less heat-sensitive and perform better in dim conditions.
  • They emit far lesser pollutants compared to their full-sized counterparts.
  • These are cheaper than traditional solar panels.
  • Other than the extreme rough environment, these remain comparatively unmoved by weather conditions.

Disadvantages of TFPV

  • Efficiency is a significant issue with most types hovering around 15 percent mark.
  • These are thinner than the traditional cells meaning that they require more space to generate the same level of electricity.
  • They are fragile and need careful handling.
  • These panels take more time to cool down.
  • These are often difficult to manufacture on a large scale.

Conclusion

As per Thin-film Solar Cell Market, 2020, thin-film solar cells will grow at a CAGR of around 9.8 percent every year till 2024. It will reach $9950 million in 2024, up from $6230 million in 2019. Even though the pandemic may halt its unprecedented growth for a while, the tryst to replace fossil energy with renewable will inevitably propel its market in the coming months. 

Also, the reducing cost of installation can be the torchbearer and woo more people to adopt solar cells in the future. Plus, we are expecting new tech such as bifacial solar, solar tiles, transparent solar panels, and similar already threatening to change the TFPV landscape soon.

 

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