Solar panels are designed to convert as many photons as possible into usable energy. For years, scientists from various disciplines have worked tirelessly to improve the efficiency of photovoltaic devices. However, current technologies are still constrained by physical limitations.
Recently, researchers from the University of Pennsylvania and Drexel University announced a breakthrough in solar cell design. This new model not only promises to reduce manufacturing costs and make production easier, but also significantly increases energy conversion efficiency.
Traditional solar cells operate by absorbing light, which excites electrons and creates an electric current. To do this, they rely on two materials: one that absorbs light and another that conducts electricity. Once an electron moves from the light-absorbing material to the conductive one, it cannot return.
However, there exists a special class of materials that allow electrons to flow in a specific direction when exposed to light—without needing to switch between different materials. This phenomenon is known as the "photovoltaic bulk effect," rather than the traditional "interface effect" found in most solar cells.
Although this effect was discovered in the 1970s, it wasn't widely used because it only converted ultraviolet light, while most of the sun’s energy comes from visible and infrared wavelengths. Now, researchers believe they've found a way to harness this effect for broader use.
The key lies in finding a material that can exhibit the photovoltaic bulk effect while also absorbing visible light. This could simplify the production process and help overcome the Shockley-Queisser Limit—a theoretical maximum efficiency limit due to energy losses during electron transitions.
Imagine sunlight as rain falling on you, with each frequency representing a different type of currency. The bandgap of a material determines the lowest "denomination" of energy it can capture. By using the right material, we can maximize the energy harvested from each photon.
This research started five years ago, with theoretical work on a new compound. The team developed a method to create a material that combines a "parent" material with a final material, adjusting the bandgap to absorb visible light. Through precise mixing and heating, they produced crystals with the desired properties.
One such structure is called a perovskite crystal. These materials have a symmetric crystal lattice that allows atoms to move freely, making them non-polar. But when two types of metal atoms are involved, the structure becomes polar, enabling directional electron movement.
After several trials, the team successfully created a material containing potassium niobate, which showed promising photovoltaic properties. Using advanced techniques like X-ray crystallography and Raman spectroscopy, they confirmed its ability to generate a bulk photovoltaic effect.
The bandgap of the material can be tuned by adjusting the amount of niobium niobate, offering advantages over traditional interface-based solar cells. As more niobium is added, the bandgap shifts into the visible range, increasing efficiency.
Another approach to bypass the Shockley-Queisser Limit involves multi-junction solar cells with varying bandgaps. While effective, this increases complexity and cost. The new material family offers a simpler solution, covering the entire solar spectrum in a single material.
This discovery marks a significant advancement in solar technology. The materials used are affordable, non-toxic, and abundant—unlike traditional semiconductor materials. The study was led by Andrew M. Rappe and Ilya Grinberg, with contributions from researchers at both universities.
Published in *Nature*, the research was supported by multiple organizations, including the US Department of Energy and the National Science Foundation. The team included students and faculty from both institutions, highlighting the collaborative effort behind this breakthrough.
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