Room-Temperature\nProcessed Nb₂O₅ as the Electron-Transporting\nLayer for Efficient Planar Perovskite Solar Cells

Abstract

In\nthis work, we demonstrate high-efficiency planar perovskite solar\ncells (PSCs), using room-temperature sputtered niobium oxide (Nb₂O₅) as the electron-transporting layer (ETL). Widely\nspread ETL-like TiO₂ often requires high-temperature (>450\n°C) sintering, which is not desired for the fabrication of flexible\ndevices. The amorphous Nb₂O₅ (labeled as a-Nb₂O₅) ETL, without any heat treatment, can give a\nbest power conversion efficiency (PCE) of 17.1% for planar PSCs. Interestingly,\nthe crystalline Nb₂O₅ (labeled as c-Nb₂O₅), with high-temperature (500 °C) annealing, results\nin a very similar PCE of 17.2%, indicating the great advantage of\na-Nb₂O₅ in energy saving. We thus carried out\na systematical investigation on the properties of the a-Nb₂O₅ film. The Hall effect measurements indicate both high\nmobility and conductivity of the a-Nb₂O₅ film.\nKelvin probe force microscopy measurements define the Fermi levels\nof a-Nb₂O₅ and c-Nb₂O₅ as −4.31 and −4.02 eV, respectively, which allow efficient\nelectron extraction at the Nb₂O₅/perovskite\ninterface, regardless of the additional heat treatment on Nb₂O₅ film. Benefitting from the low-temperature process,\nwe further demonstrated flexible PSCs based on a-Nb₂O₅, with a considerable PCE of 12.1%. The room-temperature processing\nand relatively high device performance of a-Nb₂O₅ suggest a great potential for its application in optoelectrical\ndevices.