Highly controllable and reproducible one-step synthesis of β-NaYF4:Er3+@NaYbF4@NaYF4 upconversion nanoparticles for Sb2(S,Se)3 solar cells with enhanced efficiency

Abstract

Using multilayer structures of upconversion nanophosphors is widely considered an effective and necessary strategy to achieve efficient luminescence. However, the synthesis of high-quality upconversion nanoparticles in a controllable and reproducible manner remains a challenge, especially for the monodisperse growth of core–shell–shell nanocrystals. Herein, we present a well-designed heating strategy that realizes the one-step synthesis of a hexagonal NaYF₄ host with ideal particle size and shape and further enables us to accomplish the successive growth of a spherical core containing an activator and conformal dual shells containing a sensitizer. In particular, we discuss the upconversion luminescence mechanism of Yb³⁺/Er³⁺ co-doped nanoparticles in detail, which were further introduced into Sb₂(S,Se)₃ solar cells as an extra light harvester, yielding a nominal power conversion efficiency of 9.17%. The present work helps to further clarify the effect of thermal conditions on the crystal growth and luminescence properties of upconversion nanoparticles, which is important for their practical applications.