Thin film solar panels

Thin film solar panels are a type of photovoltaic (solar) technology designed to convert sunlight into electricity. They stand out from traditional silicon-based solar panels mainly due to their use of very thin layers of photoactive materials, which are deposited onto a substrate such as glass, plastic, or metal. To understand thin film solar panels, it helps to know a bit about how solar panels in general work.

All solar panels work using the photovoltaic effect. When sunlight hits a material that has photovoltaic properties, the energy from the light knocks electrons loose from atoms within the material. These loose electrons can then flow in a controlled way, creating an electric current. This electricity can be used right away or stored in batteries for later use.

The most commonly recognized type of solar panel is made from crystalline silicon wafers. These are fairly rigid and thick compared to what we see in thin film panels. A thin film solar panel, by contrast, is created by depositing extremely thin layers—sometimes just a few micrometers thick—of photovoltaic material onto a substrate. The entire thickness of a thin film solar cell is often hundreds of times thinner than a conventional silicon wafer cell.

There are several types of materials used for thin film solar panels. The three most common are amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS).

Amorphous silicon panels were some of the first thin film panels on the market. These use silicon, just like traditional panels, but the silicon is not organized into crystals. Instead, it lacks long-range order, giving it the name “amorphous.” The result is a material that’s not quite as efficient at converting sunlight into electricity, but it is much thinner and flexible.

Cadmium telluride panels use two elements, cadmium and tellurium, combined into a compound that does an excellent job at absorbing sunlight. These are currently among the lowest-cost thin film options and are used for large-scale applications such as solar farms. However, concerns over the toxicity of cadmium have somewhat limited their use, particularly for home installations.

Copper indium gallium selenide panels, commonly referred to as CIGS panels, use a combination of four elements. They’re known for relatively high efficiency among thin film options and for their ability to be deposited on flexible substrates, allowing them to be used in places where ordinary rigid panels can’t go.

The key manufacturing difference in thin film panels comes from the way these materials are deposited. Rather than slicing wafers from a solid crystal, the manufacturing process for thin film involves one or more steps where the active material is sprayed, sputtered, or otherwise coated onto a sheet. This approach makes for a lighter, more flexible product, and it can also be cheaper in terms of materials and energy required.

Putting this all together, here’s how a thin film solar panel works in practice. Sunlight strikes the surface of the thin photovoltaic layer. The photons, or particles of sunlight, interact with the atoms in the photoactive material. This interaction causes electrons to gain enough energy that they break away from their atoms, leaving behind what are called "holes." Both the electrons and the holes then move in opposite directions through the material, encouraged by internal electric fields that result from how the layer is manufactured. These moving electrons are collected by thin electrical contacts on the top and bottom of each cell, creating a flow of electricity.

Under the glass or protective plastic surface of the panel, the thin film layers are stacked much like the layers of a cake. At the bottom is the substrate, often glass or flexible plastic. Above this is a conductive “back contact” layer. Next comes the thin, light-absorbing semiconductor layer, which is the heart of the cell and the site of the photovoltaic effect. On top of it, a transparent conducting layer allows sunlight to pass through but can also collect the electrons.

These thin film solar panels have several advantages over conventional solar panels. Because they use much less material, they are lighter and often more flexible, which means they can be used in places standard panels can’t—such as on curved surfaces or where weight is a concern. The manufacturing methods also allow for the possibility of making very large sheets of solar material, sometimes as continuous rolls, which can be installed quickly over a broad area.

Thin film solar panels also perform somewhat better in low-light conditions and at higher temperatures than their crystalline silicon counterparts. Their efficiency is generally lower, which means more surface area is needed to generate the same amount of electricity, but for certain applications—like building-integrated solar panels, portable solar chargers, and even some large-scale solar farms—the tradeoff can be worth it for the cost and flexibility benefits.

However, thin film solar panels do have limitations. Their overall energy conversion efficiencies remain lower compared to premium crystalline silicon panels, meaning you typically need more thin film panel area to get the same output. Some thin film technologies also use rare or hazardous materials, which raises environmental and supply concerns. Over time, research continues to improve the performance and sustainability of thin film options.

In summary, thin film solar panels represent an innovative approach to converting sunlight into usable energy. By using extremely thin layers of specific photovoltaic materials, they offer unique benefits such as flexibility, light weight, and lower production costs. While they may not always match the efficiency of traditional silicon panels, their distinctive characteristics make them well-suited to a wide range of novel and growing solar applications.