This paper gives an overview on the recent advances on the oxide/metal/oxide (OMO) on flexible plastic substrates and their applications as electrodes for organic and perovskite solar cells. The morphological, optical and electrical characteristics of different type of OMO electrodes such as: IMI (ITO/Metal/ITO), ZAZ (ZnO/Au or Ag/ZnO), NAN (NiO/Ag/NiO), TAT (TiO2/Ag/TiO2), DMD (MoO3/Ag/MoO3, SnO2/Ag/SnO2 etc.) collected from literature are presented and analyzed. This analysis allows to identify the most promising materials and the best choices in term of layers thickness for obtaining high quality electrodes with high transmission coefficients, high electrical conductivity and low roughness. The solar cells performances using these three layer electrodes are compared with those of the same devices in the classical configuration using ITO or FTO on plastic substrates as bottom electrodes or Au and Ag silver as top electrodes. It results a mean variation of about ±15% in efficiency performances in function of materials or technologies. The organic or perovskites solar cells classical configuration is: glass or PET substrate/ITO or FTO bottom electrodes/active layers/Au or Ag top electrodes. In the new configuration the usual bottom or top electrodes are replaced with OMO electrodes. Hence the new configurations are: 1) PET substrate/OMO bottom electrode/active layers/Au or Ag top electrode, or 2) PET substrate/ITO or FTO bottom electrode/active layers/OMO This last configuration lead to the developed of a new class of tandem or semi-transparent flexible solar cells based on organic or perovskite materials, which performances are very competitive with those deposited on classical configurations. The advantage of OMO are their mechanical, electrical and optical stability and their reduced cost by the reduction or suppression of some rare materials such as ITO.