What Materials Are Used In Pv Cells?

Photovoltaic (PV) cells, also known as solar cells, are devices that convert sunlight into electricity. PV cells work through the photovoltaic effect, in which photons from sunlight knock electrons loose from the atoms in the cell, causing electricity to flow. The PV effect was first observed in 1839 by French physicist Edmond Becquerel. The first silicon solar cell capable of converting enough sunlight into power to run electrical equipment was created in 1954 by researchers at Bell Laboratories.

Today, PV cells are commonly used in solar panels to produce solar power from sunlight. They provide a clean, renewable way to generate electricity without producing greenhouse gas emissions or requiring fuel. The use of solar PV systems has grown at an exponential rate due to concerns about climate change and increasing energy demands. PV cells are an important technology for generating renewable energy and reducing dependence on fossil fuels.

To produce electricity, PV cells need to absorb light. When light shines on a PV cell, the energy from the photons of light knock electrons loose from the atoms in the cell’s material, allowing the electrons to flow through the material to produce electricity. The energy knocks loose electrons on one side of the PV cell to create free negative charges, while leaving positively charged “holes” on the other side of the cell. The built-in electric field within the PV material then forces the electrons to flow in one direction across the cell, which is collected as electrical current. This current can then be used to power electrical devices or be fed into the grid.

Table of Contents

Silicon

Silicon is the most common semiconductor material used in photovoltaic (PV) cells today. It offers a good balance between efficiency, stability, and cost-effectiveness. Some key properties of silicon that make it suitable for PV cells include:

Abundant availability – Silicon is the second most abundant element in the Earth’s crust after oxygen.

Just right bandgap – Silicon has a bandgap of 1.1 eV, which allows it to absorb visible light efficiently for PV conversion while keeping thermalization losses low.
Low toxicity – Silicon is non-toxic, making it safe to handle and environmentally benign.
Excellent electronic properties – Silicon has high carrier mobilities, making it a good semiconductor material for electronics.

There are a few different types of silicon used in PV cells:

Monocrystalline silicon – Grown as a single continuous crystal, giving the highest efficiencies but higher production costs.
Polycrystalline silicon – Made from multiple silicon crystals, lower cost but also lower efficiency.

Amorphous silicon – Non-crystalline form allowing thin flexible cells, but with further reduced efficiency.

Silicon PV cells are manufactured by purifying raw silicon, growing it into ingots, slicing wafers, and fabricating the wafers into cells through steps like doping, surface texturing, and contact printing. Cells are then connected and encapsulated into PV modules.

Cadmium Telluride

Cadmium telluride (CdTe) is a semiconductor material that is commonly used as the absorbing layer in thin-film solar cells. Some key properties and characteristics of CdTe PV cells include:

Properties

– Direct band gap of 1.5 electronvolts, close to the optimal band gap for PV conversion efficiency.

– High absorption coefficient, allowing CdTe PV cells to absorb sunlight efficiently using thin layers of material.

– Cadmium (Cd) and tellurium (Te) form a stable crystalline structure that is durable.

Advantages

– Low manufacturing costs compared to silicon cells, as CdTe can be deposited as a thin film.

– High efficiency, with lab cell efficiencies over 22% and commercially available modules around 16-19% efficient.

– Performs well in low/diffuse light conditions.

Disadvantages

– Tellurium is a rare element, which could limit large-scale manufacturing.

– Cadmium is toxic, requiring safe handling procedures.

– Efficiency degrades faster than silicon PV cells at high temperatures.

Manufacturing

CdTe PV cells are produced by depositing a thin layer of n-type cadmium sulfide followed by a thicker p-type CdTe layer onto a glass substrate. Various techniques can be used for the deposition processes, including close-space sublimation, vapor transport deposition, sputtering, and electrodeposition. The manufacturing process and equipment is relatively simple and low-cost compared to crystalline silicon cells.

Copper Indium Gallium Selenide

Copper indium gallium selenide (CIGS) is a thin-film solar cell material composed of copper, indium, gallium, and selenium. CIGS has emerged as a promising material for photovoltaics due to its high efficiency and low cost potential.

Some key properties and advantages of CIGS solar cells include:

High light absorption – CIGS absorbs sunlight strongly, allowing the use of thin films (1-2 microns thick). This reduces material costs.
High efficiency – Laboratory CIGS cells have reached efficiencies over 22%. Manufactured modules achieve 15-19% typically.

Flexible – CIGS cells can be deposited on flexible substrates, enabling innovative applications.
Low temperature processing – CIGS films are deposited at temperatures of 400°C or less, enabling use of cheaper substrate materials.

However, there are some disadvantages to CIGS technology as well:

Indium is rare and expensive – CIGS requires a high amount of indium, which may limit large-scale production.
Toxic selenium – CIGS contains selenium, which requires careful handling during manufacturing.
Moisture sensitivity – CIGS solar cells can be prone to degradation when exposed to moisture.

CIGS solar cells are manufactured by depositing thin layers of the copper, indium, gallium, and selenium elements onto a substrate material through a process like co-evaporation or sputtering. The CIGS absober layer is only 1-2 microns thick. Various chemical treatments and buffer layers optimize performance. Modules are completed by adding external glass sheets and encapsulant.

With its high efficiency potential and ability to be deposited on flexible substrates, CIGS is a promising PV technology. However, work is still needed to improve manufacturability and minimize production costs. Wider deployment will depend on addressing challenges around the rarity of indium and selenium.

Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are a relatively new type of photovoltaic cell that use a semiconductor formed between a photosensitized anode and an electrolyte to convert sunlight into electricity. The anode is typically composed of a layer of titanium dioxide nanoparticles coated with a light-absorbing dye. When the dye absorbs sunlight, it injects electrons into the titanium dioxide, generating a flow of electrons between the anode and the cathode. The electrolyte replenishes the dye with electrons to keep the process going.

One of the main advantages of DSSCs compared to traditional silicon solar cells is their low manufacturing costs, as the materials used are inexpensive and the manufacturing process is simple. Additionally, DSSCs can work efficiently even in low-light conditions and indirect sunlight. They also have a fairly good conversion efficiency, typically around 10-12%.

However, DSSCs also have some disadvantages. The electrolyte liquid can potentially leak and the dyes tend to degrade over time when exposed to the sun. The cells also require an external bias and may have stability issues. Ongoing research aims to replace the liquid electrolyte with solid-state alternatives and improve the robustness and lifetime of the dyes used.

Research on DSSCs remains fairly active as they have the potential to provide low-cost solar electricity. Scientists are working to further improve their efficiency and stability through modifications to the cell components and architecture. With additional improvements, DSSCs could become a viable option for more widespread solar applications in the future.

Perovskites

Perovskite solar cells are a promising new material that has emerged as a highly efficient and low-cost alternative to traditional silicon solar cells. Perovskites have a crystalline structure with the chemical formula ABX3, where A and B are two cations of different sizes, and X is an anion that bonds to both. The most common perovskite used in solar cells is methylammonium lead trihalide (CH3NH3PbX3).

Perovskites have excellent optical and electronic properties that make them ideal absorbers for solar cells. They have a high absorption coefficient, allowing them to absorb light efficiently, as well as long diffusion lengths for both electrons and holes, enabling efficient charge collection. Additionally, perovskites can be fabricated using low-temperature solution processing methods, which drastically reduces manufacturing costs compared to traditional silicon cells.

Researchers have achieved extraordinary improvements in the efficiency of perovskite solar cells in recent years, with certified efficiencies now reaching over 25%. There are still challenges to overcome in terms of long-term stability and scalable manufacturing, but perovskites represent one of the most promising technologies to enable widespread adoption of low-cost, highly efficient solar power. With continued research and development, perovskites hold tremendous potential to reshape the solar industry and usher in a new era of renewable energy.

Organic PV Cells

Organic photovoltaic cells (OPVs) use organic electronics, hydrocarbon compounds that are carbon-based, as the photoactive layer that absorbs light. The active layer is sandwiched between two electrodes. OPVs can use flexible plastic substrates as a base, allowing the cells to be lightweight and bendable. This gives them unique advantages in terms of portability and integration into fabrics or other structures.

Some commonly used organic compounds in OPVs include polymers like poly(3-hexylthiophene) (P3HT), phenyl-C61-butyric acid methyl ester (PCBM), and poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT). Researchers are developing new organic compounds to improve the efficiency and stability of OPVs.

A key benefit of organic solar cells is their mechanical flexibility compared to traditional silicon cells. The materials can be deposited on flexible plastic substrates using roll-to-roll manufacturing, similar to newspaper printing presses. This makes OPVs lightweight, thin, bendable and even semi-transparent. Their flexibility and simple manufacturing gives OPVs the potential for new applications like wearable solar, building-integrated solar, and integrating solar onto curved surfaces like cars or tents.

Current research on OPVs focuses on improving their efficiency to be cost-competitive with silicon-based PVs, as well as improving their stability to withstand long-term light exposure and oxygen/moisture. Scientists are developing new organic semiconductor materials, device structures, and manufacturing techniques to address these challenges.

Quantum Dot Cells

Quantum dot solar cells are an emerging type of solar cell technology that utilize quantum dots as the photovoltaic material. Quantum dots are tiny nanocrystals made of semiconductor materials that exhibit unique optical and electronic properties. When exposed to light, an electron-hole pair is generated in the quantum dot which can be extracted as electricity.

Some of the key properties of quantum dot solar cells include:

Tunable bandgap – By controlling the size of the quantum dots during manufacturing, the bandgap can be tuned to absorb specific wavelengths of light.
High theoretical efficiencies – Quantum confinement in the dots can enable efficiencies exceeding the Shockley-Queisser limit.
Low cost materials – Quantum dots are made from abundant, inexpensive materials like lead sulfide or cadmium selenide.

Quantum dot solar cells can be manufactured using simple, low-cost techniques like spin coating or spray deposition. Extensive research is being conducted to improve the power conversion efficiencies and stability of quantum dot cells. Some active areas of research include:

New quantum dot synthesis methods to improve uniformity and tunability of dots.
Understanding and controlling recombination processes in quantum dots.

New architectures like quantum dot-sensitized solar cells.
Hybrid tandem designs with silicon bottom cells.

While still in the early stages of development, quantum dot photovoltaics show great promise as a viable solar technology. With continued research and engineering, quantum dot cells may become a competitive renewable energy source in the future.

Comparison of Materials

When considering what PV cell material to use, it’s important to weigh the pros and cons of each in terms of efficiency, costs, and other factors.

Silicon

Silicon PV cells have good conversion efficiencies, typically around 15-20%. Monocrystalline silicon is more efficient but more expensive than multicrystalline silicon. However, silicon panels tend to be relatively large, rigid, and heavy. Silicon also degrades in hotter temperatures.

Cadmium Telluride

Cadmium telluride (CdTe) PV cells have lower efficiencies than silicon, around 10-15%, but are less expensive to manufacture. CdTe performs better than silicon in higher temperatures. The use of cadmium has raised some environmental concerns.

CIGS

Copper indium gallium selenide (CIGS) PV cells have efficiencies of 10-15% and can be made flexible and lightweight. However, indium is relatively rare and costs are still high compared to other thin-film technologies.

Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSC) offer a less expensive option, but have lower efficiency of around 11%. The liquid electrolytes used can also freeze in colder temperatures.

Perovskites

Perovskite PV cells are emerging as a promising new material with high efficiencies, but they currently have issues with toxicity, instability, and durability. More R&D is needed.

Overall, each PV cell material has advantages and disadvantages in terms of conversion efficiency, costs, flexibility, and environmental factors. Silicon remains the dominant material for now, but alternatives are rapidly evolving.

Future Outlook

The future of photovoltaic cell materials looks promising, with several emerging materials showing potential to improve efficiency and lower costs. Some of the most exciting emerging PV materials include:

Perovskite-silicon tandem cells – Combining perovskites with silicon in a tandem configuration allows each material to convert light from a different part of the solar spectrum. This could enable efficiencies over 30%.

Organic-inorganic hybrid perovskites – Tuning the composition of perovskites could enable flexible, lightweight solar cells ideal for new applications.
Quantum dot solar cells – Quantum dots can be tuned to absorb specific wavelengths, enabling theoretical efficiencies as high as 66%.
Organic photovoltaics – Organic PV could enable lightweight, flexible, low-cost solar cells using roll-to-roll manufacturing.

With continued research and innovation, the performance and economies of scale of these novel PV technologies will improve. This will open up new applications for solar power and support the continued growth of renewable electricity worldwide.