title: Highly Efficient LiYF4:Yb(3+), Er(3+) Upconversion Single Crystal under Solar Cell Spectrum Excitation and Photovoltaic Application.
abstract: Luminescent upconversion is a promising way to harvest near-infrared (NIR) sunlight and transforms it into visible light that can be directly absorbed by active materials of solar cells and improve their power conversion efficiency (PCE). However, it is still a great challenge to effectively improve the PCE of solar cells with the assistance of upconversion. In this work, we demonstrate the application of the transparent LiYF4:Yb(3+), Er(3+) single crystal as an independent luminescent upconverter to improve the PCE of perovskite solar cells. The LiYF4:Yb(3+), Er(3+) single crystal is prepared by an improved Bridgman method, and its internal quantum efficiency approached to 5.72% under 6.2 W cm(-2) 980 nm excitation. The power-dependent upconversion luminescence indicated that under the excitation of simulated sunlight the (4)F(9/2)-(4)I(15/2) red emission originally results from the cooperation of a 1540 nm photon and a 980 nm photon. Furthermore, when the single crystal is placed in front of the perovskite solar cells, the PCE is enhanced by 7.9% under the irradiation of simulated sunlight by 7-8 solar constants. This work implies the upconverter not only can serve as proof of principle for improving PCE of solar cells but also is helpful to practical application.
authors.forename: Xu
authors.initials: X
authors.lastname: Chen
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University , 70 Nanyang Drive, Singapore 637457.
authors.forename: Wen
authors.initials: W
authors.lastname: Xu
authors.forename: Hongwei
authors.initials: H
authors.lastname: Song
authors.forename: Cong
authors.initials: C
authors.lastname: Chen
authors.affiliation: Key Laboratory of Photo-electronic Materials, Ningbo University , Ningbo, Zhejiang 315211, PR China.
authors.forename: Haiping
authors.initials: H
authors.lastname: Xia
authors.affiliation: Department of Physics, Nanyang Normal University , Nanyang 473000, PR China.
authors.forename: Yongsheng
authors.initials: Y
authors.lastname: Zhu
authors.forename: Donglei
authors.initials: D
authors.lastname: Zhou
authors.forename: Shaobo
authors.initials: S
authors.lastname: Cui
authors.forename: Qilin
authors.initials: Q
authors.lastname: Dai
authors.affiliation: Key Laboratory of Photo-electronic Materials, Ningbo University , Ningbo, Zhejiang 315211, PR China.
authors.forename: Jiazhong
authors.initials: J
authors.lastname: Zhang
keywords: internal quantum efficiency; perovskite solar cell; power conversion efficiency; simulated sunlight; upconversion single crystal