Over the past few years, solar cells with an organo metal halide perovskite structure have been well studied and attracted attention due to their excellent basic properties such as diffusion length of long charge carriers, good electrical properties, and light absorption coefficient, as well as easy and inexpensive solution processability. According to the efficiency chart, perovskite solar cells have achieved efficiencies of 22.1% in 2016 through rapid development with efficiency starting at 3.8%. However, despite these high efficiencies, one of the biggest problems of perovskite solar cells is the low stability and reliability of the devices in the atmosphere. For commercialization of perovskite solar cells, it is necessary to analyze and improve stability and efficiency. In the structure of the device, the electron transporting layer (ETL) and the hole transporting layer (HTL) transport charges, respectively, and mainly organic materials are used. The stability of the device can be enhanced by inserting a charge transporting layer of an inorganic material such as NiO_x, ZnO, and VO_x, which is superior in stability to organic materials such as PEDOT: PSS and Spiro-OMeTAD. Among them, p-type VO_x with wide bandgap is used as HTL and can replace PEDOT: PSS. It is also important to note that in such a stacked heterojunction solar cell structure, band bending occurs due to different band gaps. Due to the non-optimization of conduction band offset (CBO) and valence band offset (VBO) at the interface between the absorption layer and the charge transport layer, it is possible to secure a smooth movement path of electrons and holes, and conversely, recombination of electrons and holes can be a cause of reduction in efficiency. Perovskite solar cells are also attracting attention as a strategy for improving efficiency at the interface between the charge transporting layer and the absorber layer. In this study, the efficiency difference and electronic structure analysis were carried out in planar heterojunction structure with ITO/VO_x/Perovskite/PCBM/ZnO/Al structure fabricated by two process methods. The VO_x buffer layer was deposited by vacuum deposition using RF magnetron sputtering and spin casting method. The VBM and core levels at the interface were measured using optical bandgap and depth profile x-ray photoelectron spectroscopy. After that, CBO and VBO values were derived from the calculations and the mechanism of electron and hole transport was clarified. As a result, it has been confirmed that the perovskite solar cell fabricated by the RF sputter process has an efficiency of about 13% and the device manufactured by the spin casting method has an efficiency of about 8%, and the reason for the difference efficiency is explained in relation to the electronic band structure.