Cong Chen, PhD, is a Full Professor at Hebei University of Technology (HEBUT), China. He is the youngest special-term “Yuanguang scholar” in HEBUT. His main research interest is the design of solar cells with high efficiency. Hongwei Song, PhD, is a Full Professor at Jilin University, China. He has published over 300 scientific papers and two book chapters. His research interests focus on spectral physics and applications of rare earth ions and optoelectronics.