Fullerene derivative thin films have been widely used in inverted-type perovskite solar cells as the electron transport layer (ETL) and hole blocking layer. However, the smooth contact at the interface between the hydrophobic [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and hydrophilic CH3NH3PbI3 (MAPbI3) thin film has not yet been completely understood. The contact at the PCBM/MAPbI3 interface strongly influences the photovoltaic performance. The photovoltaic devices were characterized by measuring the light intensity-dependent current density–voltage (J–V) curves and impedance spectra, which show that the contact at the PCBM/MAPbI3 interface simultaneously influences the shunt resistance (carrier recombination) and series resistance (interfacial contact). In addition, x-ray diffraction patterns, atomic force microscopic images, absorbance spectra and photoluminescence spectra were used to explore the contact at the PCBM/MAPbI3 interface. The experimental results show that the flat MAPbI3 thin film cannot be completely covered by a PCBM thin film and thereby results in the s-shape characteristic in the J–V curve of the resultant solar cells. The s-shaped J–V curve can be suppressed by increasing the crystallinity and surface roughness of the MAPbI3 thin film. With the use of an interface modification layer in between the PCBM thin film and Ag cathode, the power conversion efficiency of MAPbI3 solar cells can be increased from 10.50% to 13.71%.

Highly efficient and stable semi-transparent CH3NH3PbI3 perovskite photovoltaic cells are realized by using an ITO/MoOx bilayer conductive oxide as the anode electrode with a cyclopenta[2,1-b;3,4-b']dithiophene (CT) based hole-transport material (HTM), which allows bifacial illumination from both sides of the electrodes. The wide bandgap MoOx thin film is not only to be an electron blocking layer, but also to be a passivation layer which can withstand the excessive energy bombardment during the magnetron sputtering process for the deposition of a high-quality ITO thin film. Atomic-force microscopy images, transmittance spectra and water-droplet contact angle images show that the interfacial contact between MoOx and hole transport layer (HTL) strongly influences the short-circuit current density (JSC) and fill factor (FF). The highest power conversion efficiency (PCE) values for the bifacial perovskite solar cells (0.16 cm2) and modules (11.7 cm2) are 16.38% and 14.96%, respectively. In addition, the PCE of the ITO/MoOx/CT-HTM based perovskite solar module decreases slowly toward a stable value (∼11%) for more than 700 h under wet environment conditions (70 ± 5 RH%).

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