title: New Insight into the Angle Insensitivity of Ultrathin Planar Optical Absorbers for Broadband Solar Energy Harvesting.
abstract: Two challenging problems still remain for optical absorbers consisting of an ultrathin planar semiconductor film on top of an opaque metallic substrate. One is the angle-insensitive mechanism and the other is the system design needed for broadband solar energy harvesting. Here, first we theoretically demonstrates that the high refractive index, instead of the ultrathin feature as reported in previous studies, is the physical origin of the angle insensitivity for ultrathin planar optical absorbers. They exhibit omnidirectional resonance for TE polarization due to the high complex refractive index difference between the semiconductor and the air, while for TM polarization the angle insensitivity persists up to an incident angle related to the semiconductor refractive index. These findings were validated by fabricating and characterizing an 18 nm Ge/Ag absorber sample (representative of small band gap semiconductors for photovoltaic applications) and a 22 nm hematite/Ag sample (representative of large band gap semiconductors for photoelectrochemical applications). Then, we took advantage of angle insensitivity and designed a spectrum splitting configuration for broadband solar energy harvesting. The cascaded solar cell and unassisted solar water splitting systems have photovoltaic and photoelectrochemical cells that are also spectrum splitters, so an external spectrum splitting element is not needed.
authors: School of Energy and Power Engineering, Nanjing University of Science &Technology, Nanjing 210094, China.
authors: Dong
authors: D
authors: Liu
authors: Key Laboratory of Thermal Science and Power Engineering of Ministry of Education, Beijing Key Laboratory for CO2 Utilization and Reduction Technology, Tsinghua University, Beijing 100084, China.
authors: Haitong
authors: H
authors: Yu
authors: Key Laboratory of Thermal Science and Power Engineering of Ministry of Education, Beijing Key Laboratory for CO2 Utilization and Reduction Technology, Tsinghua University, Beijing 100084, China.
authors: Yuanyuan
authors: Y
authors: Duan
authors: School of Energy and Power Engineering, Nanjing University of Science &Technology, Nanjing 210094, China.
authors: Qiang
authors: Q
authors: Li
authors: School of Energy and Power Engineering, Nanjing University of Science &Technology, Nanjing 210094, China.|School of Energy and Power Engineering, Nanjing University of Aeronautics &Astronautics, Nanjing 210016, China.
authors: Yimin
authors: Y
authors: Xuan