What Metals Are In A Pv Cell?

Photovoltaic (PV) cells, more commonly known as solar cells, are an important source of renewable energy. They convert sunlight into electricity using the photovoltaic effect, a physical process where photons from sunlight knock electrons into a higher state of energy to produce an electric current. PV cells are made of semiconductor materials like silicon and are a key technology in reducing reliance on fossil fuels.

The metals used in PV cells play a critical role in their ability to efficiently convert sunlight into electricity. Metals help transport electric charges and reflect light within the cell. The purity and type of metals impacts the performance and costs of PV modules. Understanding which metals go into a PV cell provides insight into how these renewable energy devices function.

Table of Contents

Silicon

Silicon is the semiconductor material that makes up the bulk of a PV cell. It has several properties that make it suitable for photovoltaic applications:

Abundant – Silicon is the second most abundant element in the Earth’s crust after oxygen.
Semiconductor – Silicon has semiconductor properties, meaning it conducts electricity better than an insulator like glass but worse than a pure conductor like copper. Its conductivity can be altered by introducing impurities (doping).
Band gap – Silicon has a band gap of 1.1 eV, meaning it requires light energy of 1.1 eV to excite electrons from the valence band into the conduction band. This band gap is well-suited for absorbing visible light from the sun.

Stable – Silicon is a very stable and non-reactive element, allowing silicon PV cells to withstand the environment for decades.

These properties allow silicon to effectively absorb sunlight and convert it into usable electricity through the photovoltaic effect.

Silver

Silver is a crucial metal used in solar panels, specifically for the front electrical contacts that collect the electrical current produced by the panel. Silver is highly valued for this purpose due to its high conductivity. In fact, silver is the most conductive metal on Earth, even more so than copper. This makes it excellent for collecting the electrical current generated by the PV cell and transmitting it out of the panel.

The front contacts of a solar panel are very thin layers of silver, often coated with another conductor like tin or nickel, deposited onto the silicon solar cells. The silver provides a conductive pathway for the electrons to flow out of the silicon and into the external circuit. Without these silver contacts, the electrons would have nowhere to go and the panel would not function.

Silver is relatively expensive as a raw material, but solar manufacturers prize it for its unparalleled conductive properties. Only a small amount of silver is actually needed per cell, making it an economical choice despite its high cost. The high conductivity of silver more than makes up for its price in terms of performance per unit weight.

Aluminum

Aluminum is another important metal used in solar cells, particularly for the back contacts. It is cheaper than using silver for the entire back contact, so aluminum helps lower manufacturing costs. While not as conductive as silver or copper, aluminum is still a good conductor of electricity. It can be alloyed with small amounts of other metals like silicon and magnesium to improve its conductivity. Aluminum’s reflective properties also help increase the total internal reflection in the cell, trapping more light within the active material.

Low cost and widespread availability make aluminum a practical choice for PV manufacturing. Its use as a back contact material helps balance cost and performance. With improvements in back contact passivation, aluminum-based back contact systems can approach the efficiency of silver while maintaining lower materials costs.

Copper

Copper plays an important role in photovoltaic cells as the primary material used for interconnections between cells and wiring. Thin strips of metallic copper serve as conductors, connecting the cells together into circuits and modules. Copper is well-suited for this purpose because it is an excellent conductor of electricity with high ductility. This allows it to be easily shaped into the thin ribbons or wires that connect individual solar cells.

The amount of copper used varies by cell technology, but it typically accounts for around 5% of the material content in crystalline silicon cells. Copper interconnects need to have high conductivity to minimize resistive power losses as electricity flows through the circuits. They also must be resistant to corrosion and maintain strength/flexibility through temperature changes.

In addition to cell interconnects, copper is used in cables, connectors, and junction boxes on solar panels. It connects modules to each other and to the inverter/electrical system. The high conductivity and flexibility of copper make it well-suited for this wiring application in PV systems.

Tin & Lead

Tin and lead are commonly used together in the solder that connects the silicon photovoltaic cells and other electrical components in solar panels. Solder is a metal alloy that melts at relatively low temperatures, allowing it to adhere and create strong bonds between metals. Typical solder contains roughly 60% tin and 40% lead.

The lead provides flexibility and durability to the solder, while the tin reduces melting temperature. This combination creates a solder that flows easily when heated during the PV manufacturing process to adhere silicon cells and other components together into a complete circuit, while remaining stable and conductive over decades of thermal cycles in the final panel.

Lead-based solder has excellent connectivity and conductivity properties important for solar cells, though there are health and environmental concerns with lead. This has led some manufacturers to explore lead-free solder alternatives using metals like silver, though currently lead solder remains common in PV panels.

Cadmium & Gallium

While silicon is the most common material for photovoltaic cells, some types use thin films of cadmium telluride (CdTe) or copper indium gallium selenide (CIGS) instead. Cadmium and gallium both play key roles in these alternative solar cell designs.

Cadmium telluride thin film cells rely on cadmium to absorb and convert sunlight into electricity. The cadmium serves as the cell’s photoactive layer. It offers strong solar absorption properties while being cost-effective and easier to manufacture compared to silicon. However, cadmium is a toxic heavy metal, so recycling CdTe panels is important.

Gallium arsenide is used in some high-efficiency solar cells thanks to its semiconductor properties. It has a high absorption coefficient and strong radiation resistance. Gallium is also added to the CIGS thin film cells. The gallium content helps optimize the cell’s bandgap energy for capturing photons. Too much gallium reduces voltage, while too little lowers electrical currents. The optimal Ga ratio improves overall efficiency.

Other Metals

In addition to the primary metals used in solar PV cells, there are also some trace metals that serve important functions:

Germanium – Added to silicon to improve efficiency and performance.

Tellurium – Used in some thin-film PV cells such as cadmium telluride.
Indium – Found in indium gallium selenide thin-film cells.
Selenium – Used in certain thin-film PV cells in compounds like copper indium gallium selenide.

Arsenic – Used in some gallium arsenide cells.

While only trace amounts of these metals are used, they serve important roles in the performance and efficiency of certain types of solar photovoltaic cells and technologies.

Recycling PV Cells

As solar panels become an increasingly popular source of renewable energy, recycling the metals within photovoltaic (PV) cells will be an important consideration. When solar panels reach the end of their roughly 30 year lifespan, recycling allows us to recover and reuse many of the valuable metals inside.

Some key metals found in silicon-based PV cells that can potentially be recycled include silver, aluminum, and copper. Recycling these metals decreases the need for additional mining, which helps minimize environmental damage. Recovering these precious resources also reduces costs for manufacturers.

Recycling PV cells properly allows up to 80-90% of the glass and metals to be reused. Some companies specializing in solar panel recycling use methods like shredding, hammering, cutting, and mechanical separation to efficiently extract the metals. The recycling process helps cut down on electronic waste going to landfills.

Considering the massive growth expected for the solar industry, recycling solar panels will only become more economically important over time. As more panels reach the end of their usable lifespan, recycling enables a sustainable closed-loop supply chain. Overall, recycling PV cells allows us to recover limited resources, avoid waste, and continue growing the renewable energy industry.

Conclusion

When thinking about solar PV cells, the key metals are silicon, silver, aluminum, copper, tin, lead, cadmium and gallium. Silicon forms the basic semiconductor material that absorbs sunlight and converts it into electrical current. Silver is used for its high electrical conductivity to collect and carry the current off the PV cell. Aluminum frames and backing sheets provide structural support. Copper wires and interconnects create pathways for the current to travel out of the module. And tin, lead, cadmium and gallium are used in small quantities to dope the silicon and enhance its solar-absorbing properties.

A high quality solar PV module seamlessly integrates all of these important metals to efficiently convert sunlight into clean, renewable electricity with minimal loss. While recycling processes can recover some of these metals for reuse, high purity silicon and other metals are still needed to manufacture new PV cells and modules to meet the world’s rising energy demands.