Optical Management with Nanoparticles for a Light Conversion Efficiency Enhancement in Inorganic γ-CsPbI Solar Cells.

Recently, γ-CsPbI perovskite solar cells (PSCs) have shown potential applications in optoelectronic devices, due to their high thermal stability. However, the incomplete utilization of the solar spectra especially in the near-infrared (ca. 46%) range significantly limits the power conversion efficiency (PCE). Herein, core-shell-structured NaLuF:Yb,Er@NaLuF upconversion nanoparticles (UCNPs) have been successfully synthesized and integrated into the hole transport layer for improving PCE in γ-CsPbI PSCs. Compared with the reference one, the short-circuit current density ( J) and PCE of the optimized device reached up to 19.17 mA/cm (18.81 mA/cm) and 15.86% (15.51%), respectively. Actually, due to the ultralow photoluminescence quantum yield (PLQY, < 1%) obtained in UCNPs now, we proved the generally recognized upconversion effect of UCNPs in solar cells (adjusting the light absorption edge from the visible toward NIR range for extending the spectral absorption) was negligible. A further study found the UCNPs in the PSCs primarily served as scattering centers, which is beneficial to extend the sunlight optical path by combining with scattering and reflecting sunlight, leading to producing more photoelectric current. This study suggests a new insight into understanding the underlying mechanism of UCNPs in the PSCs and provides a promising strategy via light scattering effect to enhance the device performance.