Abstarct: Using renewable and clean energy sources such as solar energy has been one of the main issues investigated, recently. Photovoltaic solar cells are one of the major achievements in this regards. Nano-structure organic solar cells newly has been investigated more than the inorganic cellsbecause of the flexibility, low production cost, less environmental pollution, and large-scale surface production. The main problem in organic solar cells is their efficiency, which is much related to the thickness of the active laxyer. In this research at first, optical simulation was carried out baxsed on the Petterson model, by use of MATLAB computer program. Three types of solar cells including bilxayer cells, blend cells, and tandem cells are investigated. In the research work has been published so far TE radiation mode has been considered. However, here the TE and TM modes of radiation are taking into account in order to optimize the radiation absorption within the active laxyer. Moreover, since the absorption of light in the cell varies by changing the thickness of each laxyer, optimization of different laxyer thickness simultaneously was considered. To simplify the relations in optical modeling in solar cells usually normal incidence of radiation is considered. Obviously, less reflection occurs by normal incidence. Therefore, it seems that the highest efficiency is obtained in this condition. However, in non-normal incidence although there is more reflection of the light, in fact longer distance of radiation into the cell results in more absorption. Therefore, two parameters including angle of incidence and the distance within the cells, are competing and must be optimized in order to obtain moreabsorption of light and consequently more efficiency. In next step optical performance of three structures bulk heterojunction organic solar cells under different angle of incidence considering absorption profile of the active laxyers is studied.