Solar cells based on organic materials offer the potential advantage of low cost, large scale,high throughput fabrication compared with conventional inorganic materials.Layers of organic dyes as thin as few nanometres are sufficient to harvest as much light as a micrometer-thick silicon solar cell.Crucial for efficient photon to electron conversion of organic solar cells is the morphology of the donor-acceptor (D/A) junction.First studies revealed that D/A junctions work best if donor and acceptors segregate on a length scale in the range of the exciton diffusion length (2-50 nm).Recently it was found that an improvement in efficiency can be made if a mixture of donors of different polarity is used.It is speculated that the morphology of D1D2/A junctions differs from the one existing in D/A-junctions.In order to gain insight into the morphology of D1D2/A junctions we propose to apply GISANS.We plan to choose C60 as electron acceptors and a mixture of two different merocyanines as electron donors.Using merocyanines with different deuteration degree in combination with GISANS will provide structure-property relations which will enable us to design new devices with higher efficiency.