Don't miss a photon! Solar cells that break through the limit

As photovoltaic technology advances, the cost of solar power generation continues to decrease steadily. According to estimates from the International Energy Agency's "World Energy Outlook," photovoltaics will become the cheapest source of electricity in history. Recently, a new material has emerged that could redefine the efficiency of solar cells, leading to a significant leap in future solar cell technology. Perhaps this could enable solar-powered cars or airplanes to sustain continuous operation solely on the solar panels they carry.

According to a report in the April 12th issue of "Science Advances," researchers at Lehigh University in the United States have developed a new material that can significantly increase the efficiency of solar panels. Prototype cells using this material as the active layer of solar cells have demonstrated an average photovoltaic absorption rate of 80%, a high photogenerated carrier generation rate, and an external quantum efficiency (EQE) as high as 190%.

This metric far exceeds the Shockley-Queisser theoretical efficiency limit of silicon-based materials. The researchers have stated that this work represents a significant leap in understanding and developing sustainable energy solutions. In the future, this innovative approach may redefine the efficiency and accessibility of solar energy.

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01

Breaking Through Traditional Theories

The external quantum efficiency (EQE) is one of the key metrics for measuring the performance of photovoltaic devices. It indicates the efficiency with which incident sunlight generates free electron-hole pairs in photovoltaic cells. Theoretically, the maximum EQE of traditional solar cells cannot exceed 100%, representing that each photon absorbed from sunlight can produce and collect at most one electron.

Currently, the EQE of single-junction solar cells is typically around 80%-90%. For instance, the EQE of silicon photovoltaic cells is generally below 90%, while the average absorption rate of copper indium gallium selenide (CIGS) thin-film photovoltaic cells is usually above 90%, making CIGS considered to have a promising future.However, some advanced materials and structures developed in recent years have proven capable of generating and collecting multiple electrons from high-energy photons, meaning that the external quantum efficiency (EQE) can exceed 100%. Moreover, these new materials exhibit higher efficiency in the utilization of low-energy photons.

02

Unique Structure

The new material can achieve an external quantum efficiency (EQE) as high as 190% due to its unique "intermediate band states." In semiconductors, "intermediate bands" refer to an energy band with lower energy that exists between the traditional valence band and conduction band within a semiconductor material.

Researchers have inserted copper (Cu) atoms into the "van der Waals gap" of two-dimensional thin-layer materials of germanium selenide (GeSe) and tin sulfide (SnS), placing the material in an "intermediate band state."

The intermediate band acts like a step, allowing low-energy photons that cannot be utilized in traditional single-junction solar cells to excite electrons from the valence band to the intermediate band, and then through a second transition from the intermediate band to the conduction band, thereby generating charge carriers that can be used by an external circuit. Therefore, materials with intermediate band states allow for the production of electron-hole pairs even when the absorbed photon energy is below the material's bandgap energy.

After the insertion of copper atoms, a new intermediate band is formed in the CuxGeSe/SnS quantum material, with the newly created sub-bandgaps being 0.78eV and 1.26eV, which are very close to the ideal sub-bandgap values for a theoretically efficient intermediate band solar cell.

In traditional single-junction solar cells, low-energy photons are not effectively utilized. For example, silicon has a bandgap width of 1.12 electron volts (eV), making it difficult to utilize photons with energy below 1.12eV. Therefore, semiconductors with intermediate band states can significantly improve the photovoltaic conversion efficiency of solar cells. The prototype of this solar cell currently exhibits high absorption in both the visible light range (where photon energy is higher) and the near-infrared range (where photon energy is lower), with an external quantum efficiency of over 190%, surpassing the Shockley-Queisser efficiency limit of traditional silicon-based solar cells.Breaking Significance

Of course, the research on this new material is still in its infancy, and further optimization of its performance and cost reduction are needed to achieve commercial application. Researchers have indicated that this breakthrough represents a significant leap in understanding and developing sustainable energy solutions.

This breakthrough holds profound significance for the field of solar energy. High-efficiency solar cells will greatly enhance the efficiency of photovoltaic power generation, making solar energy the most competitive renewable energy source. In the future, this new material is expected to be widely applied in areas such as solar-powered vehicles and aircraft, realizing the beautiful vision of continuous travel powered solely by their own solar panels.