As the demand for clean and efficient energy continues to grow, researchers and manufacturers are constantly exploring materials that improve solar cell performance. Among them, the germanium wafer has found a niche in high-performance solar technologies.
While not as widely used as silicon, germanium plays a crucial role in certain advanced applications, particularly in space exploration and multi-junction solar cells. Nevertheless, this material has a series of disadvantages and challenges, and understanding them to make the most out of its application.
In the world of renewable energy sources, the germanium solar cell stands out for its unparalleled efficiency in converting sunlight into usable electrical energy. The fundamental idea is based on the characteristics of germanium as a semiconductor.
When germanium is exposed to sunlight, it absorbs photons, which give electrons energy and cause an electric current to flow. Because germanium has a bandgap of approximately 0.66 electron volts (eV)—lower than silicon’s (1.1 eV)—it can harness a broader spectrum of light, thus enhancing its effectiveness in energy conversion.
This special quality is especially useful in areas with limited sunlight. Germanium solar cells, for example, work exceptionally well in space applications because they can effectively convert sunlight in the weak solar irradiance conditions found outside of Earth's atmosphere.
Germanium is also frequently used in multi-junction (or tandem) solar cells. The sun emits energy in a wide range of wavelengths—from ultraviolet (UV) to visible light to infrared (IR).
A single-junction solar cell (like a typical silicon cell) can only absorb a narrow band of this spectrum efficiently. The rest of the light is either not absorbed or converted efficiently, limiting the cell’s overall efficiency (typically ~15–22% for standard silicon panels).
Multi-junction solar cells solve this by layering different materials, each with a different bandgap (the energy range a material can absorb). Here’s how it works:
Germanium-based solar cells offer several advantages, such as:
Germanium’s most significant contribution is its use in multi-junction solar cells, which are currently the most efficient solar cells in the world. Under concentrated sunlight, their efficiencies exceed 40%.
The reason is that different materials in the stack absorb different parts of the solar spectrum. Germanium efficiently absorbs infrared light, which is otherwise wasted in most conventional silicon cells.
Germanium has a relatively low bandgap of 0.66 eV, making it ideal for absorbing the lower-energy, longer-wavelength (infrared) part of the spectrum that higher-bandgap materials like gallium arsenide cannot utilize effectively.
Germanium provides a very good lattice match for the epitaxial growth of other III-V materials like GaAs. This reduces defects in the crystal structure, which enhances performance and reliability in the final solar cell.
Germanium-based multi-junction cells are the standard in space missions, used in satellites, space probes, and the International Space Station. Their ability to function in extreme conditions makes them the top choice for extraterrestrial solar power.
Additionally, germanium atoms are heavier (atomic number 32) than silicon atoms (atomic number 14). This makes it resistant to radiation damage, which is crucial for space applications.
Germanium maintains good electrical performance over a range of temperatures, which is important in applications exposed to thermal cycling, such as aerospace or military-grade equipment.
However, silicon solar cells remain the most popular option worldwide, and there is a reason for that. Germanium solar cells pose several limitations, such as:
Germanium is a rare and expensive material. It is not as abundant as silicon and must be extracted as a byproduct from zinc and copper ore processing. This limited availability contributes to the high manufacturing costs of germanium-based solar cells.
As a result, they are economically unfeasible for large-scale terrestrial use, such as residential or commercial solar panels.
While germanium itself is not highly toxic, the processes involved in fabricating multi-junction solar cells often involve hazardous materials, including arsenic and phosphide compounds. This raises concerns about environmental impact and worker safety during production and disposal.
Multi-junction cells using germanium require advanced manufacturing techniques, such as metal-organic chemical vapor deposition (MOCVD), to grow multiple crystalline layers rapidly. This complexity increases production time and cost and limits the number of manufacturers capable of producing these cells at scale.
Germanium is more mechanically brittle than silicon, which can present durability issues during manufacturing or deployment, especially if not adequately supported or protected.
Due to the above factors—especially cost and complexity—germanium solar cells are impractical for everyday terrestrial solar applications. They are reserved for niche markets where performance outweighs cost, such as aerospace, military, or concentrated photovoltaic (CPV) systems.
Germanium solar cells represent the cutting edge of solar technology in specific, high-performance applications. Their contribution to multi-junction solar cells makes them invaluable in applications that require maximum efficiency and compact size, particularly in space exploration and concentrated solar power systems.
However, germanium's high cost, limited availability, and manufacturing complexity limit its use in conventional solar panel production. Silicon-based cells remain the most practical and affordable choice for most residential or commercial needs.
Germanium plays an important role in pushing the limits of solar cell performance. While this material has some drawbacks, such as its manufacturing costs or toxicity, it also offers unique advantages for complex applications.
As technology advances and new methods of material synthesis and recycling emerge, this versatile element may find broader applications in the future of renewable energy. Are you still unsure about what substrate you need? Contact Wafer World and let us help you!
