Organic solar cells are expected to have superior performance in terms of flexibility and low-cost fabrication. However, conventional organic solar cells usually have issues while using rare earth ITO materials and have poor long-term reliability. To seek possible solutions for these issues, we fabricated an inverted solar cell structure of PEN/PEDOT:PSS/PFN/PTB7:PC71BM/MoO3/Au, and found that the fabricated devices had considerably improved long-term reliability when stored in air without any surface passivation layer. The resultant conversion efficiency of the solar cell was 1.88%, and it decreased to 90% of its initial value after 100 h of storage in air.