NOVELTY - A composition comprises polymer (A), polymer (B) (I) and small molecule (A). The lowest unoccupied molecular orbital energy level of polymer (B) (I) is present between lowest unoccupied molecular orbital energy levels of polymer (A) and small molecule (A). The highest unoccupied molecular orbital energy level of polymer (B) (I) is present between highest unoccupied molecular orbital energy levels of polymer (A) and small molecule (A). The composition contains 10-45 wt.% small molecule (A) with respect to total weight of polymers (A) and (B) (I), and small molecule (A).    USE - Composition e.g. kit is used for forming active layer of organic solar cell (all claimed) e.g. solar photoelectric cells for rotating turbine.    ADVANTAGE - The composition provides layers with improved performance and has polymer which enhances the absorption of light and facilitates movement of charges. The active layer is thin, stable and resistant to heat. The composition provides solar cells with increased power conversion efficiency even if the amount of molecules is reduced for increasing the lifetime of the cells.    DETAILED DESCRIPTION - A composition comprises polymer (A) which absorbs light to form excitons, polymer (B) which plays a charge-bridging role and small molecule (A) which is an electron accepting material. The lowest unoccupied molecular orbital energy level of polymer (B) is present between lowest unoccupied molecular orbital energy levels of polymer (A) and small molecule (A). The highest unoccupied molecular orbital energy level of polymer (B) is present between highest unoccupied molecular orbital energy levels of polymer (A) and small molecule (A). The composition contains 10-45 wt.% small molecule (A) with respect to total weight of polymers (A) and (B), and small molecule (A). An INDEPENDENT CLAIM is included for organic solar cells, which comprises active layer comprising the composition, arranged between two electrodes.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of solar cell.