Performance enhancement of hole-transport material free perovskite solar cells with TiO2 nanorods modified with SiO2/NaYF4:Yb,Er@SiO2 for upconversion and charge recombination suppression

Hole-transport material-free (HTM-free) perovskite solar cells (PSCs) have the advantages of low manufacturing cost and excellent stability, however, the power conversion efficiencies (PCEs) of these PSCs are relatively low due to the high recombination rate at charge transport interface contacts. Herein, a novel bilayer electrontransport scaffold of SiO2/NaYF4:Yb,Er@SiO2 modified TiO2 nanorods was designed to improve the performance of HTM-free PSCs. Facilitated by the 1D nanorods structure of underneath TiO2 scaffold, photogenerated charges can be quickly transported out of perovskite film with reduced recombination, and the NaYF4:Yb,Er@SiO2 insulating capping layer can further inhibit the charge recombination by removing charge shorting pathways caused by the tangle of TiO2 nanorods with carbon back contact. Moreover, NaYF4:Yb,Er can upconvert near-infrared light into visible region that can be directly used by perovskite materials to improve the current density of corresponding PSCs. Our PSCs have an average PCE of 14.01 +/- 0.53%. We demonstrated that up-conversion of light at 980 nm was possible but up-conversion made no statistical improvement in performance.