Researchers have discovered a cost-effective alternative to using expensive precious metals like gold or silver in perovskite solar cells. Kai Zhu, a senior scientist at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), along with his colleague at Northern Illinois University, have proposed a solution that replaces the precious metal layer with a nickel-doped graphite layer combined with a bismuth-indium alloy layer. These two layers can be easily integrated into the perovskite device through a simple painting process, making it a low-cost fabrication method.
In their paper titled “Nickel-Doped Graphite and Fusible Alloy Bilayer Back Electrode for Vacuum-Free Perovskite Solar Cells,” published in ACS Energy Letters, the researchers describe their potentially disruptive technology that could reduce the infrastructure investment required for perovskite solar cell production. The current method involving gold as the back-metal electrode necessitates an expensive high-temperature vacuum-chamber process, whereas the proposed approach utilizes inexpensive materials that can be laminated onto thin films at atmospheric pressure and mild temperatures. This affordable solution is expected to accelerate the commercialization of perovskite solar cells.
The laboratory efficiency of the perovskite solar cell using the new materials was reported to be 21%, with the potential for further research to increase the efficiency closer to that of precious metal-based perovskites, which achieve a record efficiency of 26%. Although metals are better conductors of electricity than carbon, the researchers believe that the benefits of cost reduction outweigh the slight decrease in efficiency.
Perovskite solar cells are manufactured by depositing chemicals onto a substrate, with each layer serving a specific purpose. The perovskite layer acts as the semiconductor, where photons from sunlight cause electrons to move in one direction, creating a vacancy or “hole” that moves in the opposite direction, generating an electric current. Both gold and the graphite material possess the required energy level for this process.
The elimination of the precious metal layer significantly reduces the manufacturing cost of perovskite solar cells. According to the researchers’ analysis, in a perovskite-based solar plant with a gigawatt of power output, adopting the graphite/alloy bilayer could reduce costs of the contact electrodes by a factor of 4 to 1,000, depending on the other back materials used.
This cost-effective approach represents a significant advantage for the widespread adoption of perovskite solar cell technology.