Microscopic Evidence of Upconversion-Induced Near-Infrared Light Harvest in Hybrid Perovskite Solar Cells

Photon upconversion represents a promising avenue to reduce the spectral mismatch losses limiting the efficiency of solar cells. Here we studied in detail the impact of inserting Yb3+/Er3+ co-doped KY7F22 upconversion nanoparticles (UCNPs) into the different interfaces of a solution-processed mixed-cation lead mixed-halide perovskite solar cell. Besides macroscopic photovoltaic characteristics, we quantify the upconversion contribution by the light-beam induced current/fluorescence mapping technique on devices with only half of their interfaces decorated by UCNPs. Such mapping experiments offer a detailed microscopic and spectroscopic picture allowing a correlation of the electrical and optical contribution of UCNPs together with the solar cell morphology.