Electrical and Computer Engineering Department, The University of North Carolina at Charlotte
Contrary to the common assumption that the light-induced halide ion segregation in a mixed halide alloy occurs within the illuminated area, we discover that the anion segregation in a (FA,MA)Pb(BrxI1-x)3 thin film is a nonlocal effect where the Br ion are expelled from the illuminated area, forming a Br-rich ring with the size proportional to the illumination beam size, varying from mesoscopic to macroscopic scale. Specifically, we find that under illumination, within the illumination area, the photoluminescence (PL) peak is red shifted from the initial wavelength; while concurrently, the alloy PL peak is strongly enhanced in a ring area circling the illuminated area. Furthermore, the process is reversible, but non-monotonically, exhibiting ultra-low-frequency, damped oscillations between the ring and center in terms of PL intensity and position. This peculiar finding could be the first observation of an ionic plasma oscillation in solids. Interestingly, right after removing the illumination, a voltage about 0.4 V between the ring and the center is established. Our findings suggest that the “ion-segregation” phenomenon, commonly viewed as an adverse effect, could have novel applications, such as ionic patterning, self-destructive memory, and energy storage (particularly a battery directly chargeable by sunlight).
X. X. Sun, Y. Zhang, and W. K. Ge, Light: Science & Applications volume 11, 262 (2022)
Dr. Yong Zhang holds the position of Bissell Distinguished Professor in Engineering within the Department of Electrical and Computer Engineering at UNC Charlotte. He obtained his B.S. (1982) and M.S. (1985) degrees in Physics from Xiamen University, followed by his Ph.D. (1994) from Dartmouth College. Afterward, he conducted his postdoctoral research at the National Renewable Energy Laboratory (NREL) and served as a Senior Scientist. In 2009, Dr. Zhang joined UNC Charlotte as a Bissell Distinguished Professor. His research primarily revolves around the electronic and optical properties of semiconductors and related nanostructures, organic-inorganic hybrid materials, electron-phonon coupling, impurities and defects in semiconductors, and novel materials and device architectures for applications in optoelectronics, energy, and electronic-photonic integrated circuits. Dr. Zhang has over 260 publications and holds five patents. He is a Fellow of the American Physical Society.