Master structures of micro prisms with a pitch of 100^m were made by precision mi­cro machining. The substrate is made in a replication process (figure 2). Organic thin films and the electrodes are deposited on the surface by spincoating and evapora­tion respectively. Cohesion and adhesion forces lead to an increased thickness of the polymer films in the grooves of the struc­ture. This effect makes the location of the metal grid in the grooves more adequate than on the tips of the structure because the probability of direct shunts between the two metal electrodes is decreased. The mi­crogrid structure is realised by evaporation under a certain angle. The microstructure itself functions as a self aligning mask. In the first step a 200nm sacrificial layer of LiF

is evaporated under an angle of 65° relative to the normal of the substrate. This leads to an uncoated region of about 10^m width in the grooves of the structure. Normal to the substrate a 8nm Cr layer to increase the adhesion and a 100nm gold layer are evap­orated. The Au-layer on top of the LiF is removed in a lift off process in di-water in an ultrasonic bath. All grid stripes are interconnected by finally evaporated Cr-Au-layers. Thin films from standard solutions with thicknesses comparable to the planar substrate could be deposited on the structured substrate by spin-coating. PEDOT-CPP 105D was coated @2000Upm for 60sec. The films had to be dried in a vacuum oven for 1h @ 80°C. The active layer P3HT/PCBM (1:2 by wt.) was spun under argon atmosphere for 60sec @500Upm.

Prior evaporation of the 100nm thick Al — electrode, the substrate was again dried in vacuum oven @50° for 10h. From SEM- investigations it could be seen that the large ratio between the dimensions of the mi­crostructure and the thickness of the or­ganic thin films allows a relatively homo­geneous coating of 3-dimensional structure (not shown). An increased thickness of the polymer films in the grooves of the struc­ture was observed. IV-characteristics were measured under argon atmosphere using a Steuernagel AM1.5 Solar simulator (fig­ure 6). However the efficiency of 1.1% is far beyond the best published results for an ITO-based device, these inititial experiments should be regarded as a proof of principle.

Higher efficiencies are expected from further optimising of the process parameters.