Editorial Feature

The Use of Semiconductors in Solar Energy Technology

Semiconductors play a critical role in clean energy technologies that enable energy generation from renewable and clean sources. This article discusses the role of semiconductors in solar cells/photovoltaic (PV) cells, specifically their function and the types used.

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The Function of Semiconductors in Solar Cells

PV cells are primarily composed of semiconductor materials that have a higher conductivity than insulators. However, these materials are not good conductors of electricity like metals. Different types of semiconductors, such as crystalline silicon (c-Si) and cadmium telluride (CdTe), are used in solar cells.

Semiconductors in PV cells absorb the light’s energy when they are exposed to it and transfer the energy to electrons. The absorbed additional energy allows electrons to flow in form of an electrical current through the semiconductor material.

Subsequently, conductive metal contacts/grid-like lines on solar cells collect the current generated in the semiconductor. Solar cells are connected to form larger power-generating units known as solar panels.

The bandgap is a crucial property of PV semiconductors as it indicates the wavelengths of light that the material can absorb and convert into electrical energy. Solar cells can utilize the available light energy more efficiently when the bandgap of the semiconductor matches the wavelengths of the light shining on the PV cell.

PV cell efficiency indicates the effectiveness of the cell at converting light energy into electrical power. This efficiency is influenced by the wavelengths and intensity of the available light and several performance attributes of the cell.

Semiconductor Parameters that Influence the Performance and Design of Solar Cells

In a solar cell, the semiconductor’s ability to absorb visible and other radiation depends on its refractive index, absorption coefficient, and bandgap energy. Additionally, the diffusion coefficient and mobility of charge carriers influence the transport of carriers due to diffusion and drift, respectively.

The concentration of doping atoms, either the acceptor atoms that accept electrons or donor atoms that donate free electrons, determines the width of a junction’s space-charge region. Moreover, the recombination-generation processes are directly impacted by the diffusion length and lifetime of excess carriers.

Commonly Used Semiconductor Materials in Solar Cells

Silicon is one of the most abundant materials on Earth and is used extensively as a semiconductor material in PV cells. c-Si cells are composed of silicon atoms connected in a crystal lattice formation. The organized structure of the lattice increases the light-to-electricity conversion efficiency.

Solar cells manufactured using silicon are cheaper, have a long lifetime, and demonstrate high efficiency. Existing c-Si solar modules manufactured on an industrial scale have shown 18%–22% efficiencies under standard test conditions. Silicon-based cells can last 25 years and still generate 80% of their initial power after this period.

Copper indium gallium diselenide (CIGS) and CdTe are the most common thin-film PV semiconductors used to manufacture thin-film solar cells. Although CdTe cells can be manufactured in a cost-efficient manner, they have a lower efficiency compared to silicon cells.

Similarly, CIGS cells possess high efficiencies and suitable properties as PV semiconductor materials. However, the manufacturing of these materials by combining four elements is extremely challenging. Moreover, both CIGS and CdTe require greater protection than silicon to ensure long-lasting operations.

Perovskite semiconductors can be assembled easily and realize efficiencies similar to c-Si. In the last decade, the efficiencies of perovskite solar cells increased significantly from 3% in 2009 to more than 25% in 2020. However, perovskite cells have a shorter lifetime than c-Si cells.

Organic semiconductors can be tailored to improve a specific function of the solar cell, such as transparency or bandgap. Solar cells based on organic semiconductors/organic PVs can be manufactured on a large scale in a cost-efficient manner. However, organic PVs demonstrate significantly less efficiency and have shorter operating lifetimes compared to c-Si cells.

In quantum dot solar cells, electricity is conducted through nanometer-wide particles of various semiconductor materials/quantum dots. Quantum dots are available in different sizes and their bandgap can be tailored to enable them to absorb light that cannot be captured easily.

Moreover, these semiconductors can be used in combination with other semiconductors, such as perovskites, to optimize a multijunction solar cell’s performance. However, quantum dot semiconductor materials are not efficient in converting light energy to electrical current.

Several semiconductor materials can be arranged in a layered manner to synthesize multijunction solar cells with significantly improved efficiency. Multijunction solar cells can harness the energy of sunlight more efficiently compared to single junction cells as every semiconductor layer with a different bandgap can absorb a different part of the solar spectrum.

Thus, these cells have demonstrated an exceptional efficiency of more than 45%. However, multijunction solar cells are difficult to manufacture and expensive, which are major disadvantages of this approach.

Conclusion and Future Outlook

Perovskites are increasingly gaining attention as a suitable alternative to silicon as perovskite solar cells can be manufactured more easily compared to silicon cells. Typically, these materials are synthesized using materials that are cheap and abundant on Earth, such as bromine, iodine, and lead, leading to the low-cost generation of solar power.

Perovskites can better absorb the high-energy blue photons from sunlight than silicon. Each part of a tandem perovskite solar cell can be tailored to absorb different parts of the solar spectrum. However, perovskites lack the low-energy light-grabbing ability of silicon.

Tandem perovskites with a tin-lead perovskite and a conventional, lead-based high-energy absorbing cell and 23% efficiency were synthesized to address this issue. However, the high reactivity of tin with atmospheric oxygen has created defects in the crystalline lattice of the tin-lead perovskite, which disrupted the movement of electrical charges through the cell, limiting its efficiency.

To summarize, silicon semiconductors are currently playing a critical role in the large-scale manufacturing of solar cells with good efficiency and durability. In the future, all-perovskite tandems are expected to become more prevalent as they are cheaper to produce compared to silicon cells. However, more research is required to increase the efficiency and robustness of such all-perovskite tandems to make them commercially viable as silicon cells.

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References and Further Reading

Green, M. A., Ho-Baillie, A., Snaith, H. J. (2014), The emergence of perovskite solar cells. Nature Photon 8, 506–514. https://doi.org/10.1038/nphoton.2014.134

Service, R. F. (2019) To amp up solar cells, scientists ditch silicon [Online] Available at https://www.science.org/content/article/amp-solar-cells-scientists-ditch-silicon#:~:text=Now%2C%20researchers%20are%20doing%20away,to%20less%20costly%20solar%20power. (Accessed on 03 February 2023)

How a Solar Cell Works [Online] Available at https://www.acs.org/education/resources/highschool/chemmatters/past-issues/archive-2013-2014/how-a-solar-cell-works.html (Accessed on 03 February 2023)

Solar Photovoltaic Cell Basics [Online] Available at https://www.energy.gov/eere/solar/solar-photovoltaic-cell-basics#:~:text=When%20the%20semiconductor%20is%20exposed,material%20as%20an%20electrical%20current. (Accessed on 03 February 2023)

Ballentine, P., Duran, L., Anderson, E. (2008). [Online] Available at https://repositories.lib.utexas.edu/bitstream/handle/2152/47379/ballentine-2008-cleantx-analysis-on-semiconductors.pdf?sequence=2&isAllowed=y (Accessed on 03 February 2023)

SEMICONDUCTOR MATERIALS FOR SOLAR CELLS [Online] Available at https://ocw.tudelft.nl/wp-content/uploads/Solar-Cells-R3-CH3_Solar_cell_materials.pdf (Accessed on 03 February 2023)

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Samudrapom Dam

Written by

Samudrapom Dam

Samudrapom Dam is a freelance scientific and business writer based in Kolkata, India. He has been writing articles related to business and scientific topics for more than one and a half years. He has extensive experience in writing about advanced technologies, information technology, machinery, metals and metal products, clean technologies, finance and banking, automotive, household products, and the aerospace industry. He is passionate about the latest developments in advanced technologies, the ways these developments can be implemented in a real-world situation, and how these developments can positively impact common people.


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