Cobalt Oxide (CoO x ) as an Efficient Hole-Extracting Layer for High-Performance Inverted Planar Perovskite Solar Cells

CoO x is a promising hole-extracting layer (HEL) for inverted planar perovskite solar cells with device configuration ITO/CoO x /CH3NH3PbI3/PCBM/Ag. The devices fabricated according to a simple solution procedure showed the best photovoltaic performance attaining power conversion efficiency (PCE) of 14.5% under AM 1.5 G 1 sun irradiation, which is significantly superior to those of materials fabricated with a traditional HEL such as PEDOT:PSS (12.2%), NiO x (10.2%), and CuO x (9.4%) under the same experimental conditions. We characterized the chemical compositions with XPS, crystal structures with XRD, and film morphology with SEM/AFM techniques. Photoluminescence (PL) spectra and the corresponding PL decays for perovskite deposited on varied HEL films were recorded to obtain the hole-extracting characteristics, for which the hole-extracting times show the order CoO x (2.8 ns) < PEDOT:PSS (17.5 ns) < NiO x (22.8 ns) < CuO x (208.5 ns), consistent with the trend of their photovoltaic performances. The reproducibility and enduring stability of those devices were examined to show the outstanding long-term stability of the devices made of metal oxide HEL, for which the CoO x device retained PCE ≈ 12% for over 1000 h.