Though organic solar cells have a quite long, and disappointing history, a new and increasing interest is again devoted to them. Such research effort is related to the recent developments on the conjugated polymers based optoelectronics devices. During the last quarter of the XX^th century conducting and semiconducting polymers have received great scientific attention mainly due to their potential applications.

Organic thin film transistors, light emitting diodes and solar cells using conjugated polymers were achieved. The efficiency of photovoltaic devices based on conjugated polymers alone were quite poor, while promising results were obtained with the organic light emitting diodes (OLED). Therefore, in the past ten years OLEDs have attracted considerable interest. A lot of works has been done with the aim of understanding the phenomena occurring in order to improve device performance.  It has been shown that spectacular improvements can be achieved by using multilayers structures, such as hole injection layer, hole transport layer, electron transport layer and electron injection layer. When such sequence is used, at least partly, the electroluminescence is multiplied by more than one order of magnitude. A complementary approach is to blend a luminescent organic material in a polymer matrix.

Such ideas, the use of different organic materials jointly, mixing of polymers and dyes are now under study for photovoltaic elements, which justifies the new increasing attention invested in that field. Recently devices efficiencies higher than 3% have been reached, by mixing electron-donor type polymers with suitable electron-acceptors. Such configuration allows to, at least partly, overcome the limitation of the collection of the photoinduced charge carriers.

After a general presentation of the mechanisms involved in organic light emitting diodes and of the different solutions proposed to improve their efficiency, an analogy with photovoltaic devices is proposed. Then the article summarize and synthesize the main studies carried out in the last decade in that solar field. Finally some original solutions to obtain organic mixing materials are proposed.