Comprehensive studies were carried out to explore the roles of phenyl-C-61-butyric acid methyl ester (PCBM) thin films in inverted-type CH3NH3PbI3 (MAPbI(3)) based photovoltaics, including the surface morphologies, transmittance spectra, photoluminescence spectra, X-ray diffraction (XRD) patterns, Raman scattering spectra and thin-film residual stress analysis. The reduction in the photoluminescence line width indicates that the crystallinity of the MAPbI3 thin film can be increased by covering it with the PCBM thin film. The XRD patterns and Raman scattering spectra show a reduction in the compressive stress of MAPbI3 thin film when covered by the PCBM thin film. In addition, it is noted that the residual stress at the contact interface between the hydrophilic MAPbI3 and the hydrophobic PCBM can be ignored as confirmed by the results obtained with a home-made Twyman-Green interferometer. Consequently, the superior optoelectronic properties of the perovskite materials, as well as the use of a multifunctional fullerene-based thin film as the capping layer allow for the high-efficiency perovskite photovoltaics.