(DE4310206-A1)      A solar cell prodn. process involves (a) electrochemically etching through-holes in a first surface of an n-doped single crystal silicon wafer to form a perforated detached layer of the silicon; (b) forming a pn-junction in the layer by producing n-doped and p-doped regions adjacent a first main face of the layer which is parallel to the first surface; and (c) forming contacts to the n-doped and p-doped regions on the first main face so that the pn-junction is connected as a solar cell in which light incidence can occur via a second main face. opposite the first main face.    ADVANTAGE -   The contacts are formed on the reverse side of the solar cell to avoid shading and are designed for minimal ohmic loss. The elasticity of the free-standing layer allows reverse-side connection of solar cells by laying conformally on a non-flat support provided with conductor lines.    (JP6302839-A)      A solar cell prodn. process involves (a) electrochemically etching through-holes (4) in a first surface (2) of an n-doped single crystal silicon wafer to form a perforated detached layer (7) of the silicon; (b) forming a pn-junction in the layer (7) by producing n-doped (10) and p-doped (9) regions adjacent a first main face (2) of the layer which is parallel to the first surface (2); and (c) forming contacts (15, 14) to the n-doped (13, 10) and p-doped (9) regions on the first main face (2) so that the pn-junction is connected as a solar cell in which light incidence can occur via a second main face (52) opposite the first main face (2).    ADVANTAGE -   The contacts are formed on the reverse side of the solar cell to avoid shading and are designed for minimal ohmic loss. The elasticity of the free-standing layer allows reverse-side connection of solar cells by laying conformally on a non-flat support provided with conductor lines.    (DE4310206-C2)      In the method for producing solar cells, through-holes (4) are formed in an n-doped monocrystalline silicium substrate by etching electrochemically the first main surface (2), so that there is produced a perforated layer (7) supported at one end only.    Then, a p+-doped region (9) is formed by p-doping the entire layer while an n-doped region (10) includes the inside surface of the layer, so that a pn-junction is produced. The layer is covered by a mask and then, by etching the n-doped region is exposed.    The mask is removed and the p+-doped region and the exposed n-doped region are each provided with a contact (14,15), so that there is a pn-junction with the light incident over a second and opposite main surface (52).    USE/ADVANTAGE -   Suitable for solar energy installations. Light is incident from the rear and it can be used in large plants.