Researchers at Korea's Pusan National University, Kyungpook National University, Switzerland's École Polytechnique Fédérale de Lausanne (EPFL) and University of Fribourg have pioneered an approach that not only rectifies lead leakage but also focuses on interfacial passivation. The team used the method to achieve perovskite solar cells with 21.7% power conversion energy.
The presence of lead ions in perovskite solar cells not only causes lead leakage, which is hazardous to the environment, but in the presence of moisture, the perovskite tends to degrade. Multiple approaches have been suggested to resolve this issue, including encapsulating the device and compositional engineering of the perovskite light absorbers. The crown ether was found to assist in resisting degradation due to moisture for 300 hours at room temperature and 85 percent humidity. In the study, the researchers tested many crown ethers, but found that B18C6 was the best for interfacial passivation.
With B18C6, there was an increased charge carrier lifetime (or the time spent by an electron in the conduction band of a semiconductor and a hole in the valence band of a semiconductor) seen within the perovskite. The work function (or the minimum energy required to move an electron from a metal’s surface) between the hole transfer material and the perovskite was also improved.
Compared to untreated perovskites that showed signs of lead leakage, the perovskites with B18C6 showed no signs of lead leakage when a depth profile of all layers was conducted. Furthermore, while normal perovskites showed lead iodide formation when exposed to 95% humidity at room temperature for 300 hours, no such issue was observed for the perovskite passivated by B18C6.
Lead researcher Ji-Youn Seo said: “In ten years, this technology could be applied to the energy, display, and semiconductor materials industries through the heterojunction structure. If leveraged effectively, it could lead to the development of high-efficiency hydrogen production devices, high-brightness, flexible displays, and the development of three-dimensional organic and inorganic semiconductor materials and devices, contributing to leading the advancement of high-tech nations.”
