Solar panels, also known as photovoltaics, require semiconductor devices or solar cells to convert energy from the Sun into electricity. Solar cells, on the other hand, need an electric field to separate the positive and negative charges from each other to generate electricity. To achieve this field, manufacturers often dope the solar cell with chemicals. Thus, while one layer of the device carries a positive charge, the other has a negative charge. This multi-layer pattern allows electrons to move from the negative side of the device to the positive side. This is very important for the durability and performance of the machine. But chemical doping and layered synthesis also add extra costs to solar cell manufacturing.
Scientists at Berkeley Lab and UC Berkeley have devised a unique workaround that offers a much simpler method for solar cell fabrication. The solution was a crystalline solar material with a built-in electric field (materials that can be used to manufacture solar cells), which property scientists call ferroelectricity. The material was introduced in the journal Science Advances.
The new ferroelectric material produced from caesium germanium tribromide (CsGeBr3 or CBG) in the laboratory could make the construction of Solar cell devices much more accessible. Unlike conventional solar materials, CBG crystals are self-polarized. Since one side of the crystal creates a positive charge and the other a negative one, doping is unnecessary.
Besides being ferroelectric, CBG is also a lead-free halide perovskite. Halide perovskites, a recently emerging class of solar materials, are attracting researchers’ attention due to their convenience and ease of synthesis compared to silicon. However, many of the most helpful halide perovskites naturally contain lead.
According to other researchers, lead residues from the manufacture and disposal of perovskite-based solar materials can pollute the environment and cause public health problems. For these reasons, researchers began to look for new halide perovskite formulations that do not contain lead without sacrificing performance.
Peidong, currently a senior scientist in the Department of Materials Science at Berkeley Labs and professor of Chemistry and Materials Science and Engineering at UC Berkeley, is also a prominent nanomaterials expert known for his pioneering work in new solar material technologies and one-dimensional semiconductor nanowires for artificial photosynthesis. Yang says: “CBG can also develop light-responsive switching devices, sensors and super-durable memories.”
Perovskite solar layers are often made using low-cost solution coatings such as spin coating or inkjet printing. Unlike silicon, which requires a processing temperature of 1500 degrees Celsius to convert into a solar material, perovskites can be quickly processed from room temperature to 150 degrees Celsius. These lower process temperatures significantly reduce manufacturers’ energy costs.
Despite their potential contribution to the solar industry, perovskite solar materials are unlikely to be marketed anytime soon. There are challenges that researchers must first overcome in product synthesis, durability and material sustainability.