Researchers developed a method for rapidly growing a large amount of high-purity cadmium telluride (CdTe) material — a more than kilogram-sized crystal in one day. The technique, which uses a high-pressure furnace to produce large amounts of the CdTe feedstock material, is 45% more cost-effective than the industry standard and is scalable, which could make CdTe solar technology less expensive than natural gas. The crystal material produced also has better electrical properties for solar cell production than what is currently available.
CdTe photovoltaics are a newer technology than popular silicon solar cells and are competitive in terms of efficiency. They also perform better in hot and humid weather. While CdTe solar cells could provide significant advantages in cost and efficiency over silicon, they currently make up less than 10% of the solar market, mostly at the utility scale. In particular, current production methods are slow, costly, cumbersome, and lack the flexibility to customize.
The current manufacturing process involves synthesizing the CdTe material in a sealed quartz tube to contain the reaction. It takes a long time, the tubes are not reusable, and the silica glass is limited in how much heat, mass, and pressure it can take. Because of concerns about the material exploding, the industry is limited in the size of crystals they can produce. To make solar cells, the crystals are then evaporated onto glass substrate to make very thin films.
The new technique uses a strong graphite crucible, and the material is synthesized in a high-pressure Bridgman furnace. The high-pressure environment completely eliminates the possibility of explosions and also allows the researchers to easily add a high concentration of additional materials, called dopants, during the manufacturing process that improve the material’s performance.
In 2016, the team dramatically improved CdTe technology by adding phosphorus as a dopant, overcoming a 1-Volt limit that had been pursued for six decades. For this project, the researchers added arsenic as a dopant. Adding the highly volatile dopants during the feedstock manufacturing process also eliminates the need to dope after film deposition, which can cause nonuniformity issues. The researchers created crystals that are 1.2 kilograms in size but could potentially create crystals that are up to 20 kilograms.