Thin film solar cells on the base of CdTe polycristalline film
      The second material, which is wide used in mass production of of thin film panels CdTe. The films ot this material are deposted by vacuum evaporation in chambers with small distance between evaporator and substrate (close space chamber). CdTe is a material with direct optical transitions 1,5 eV. The CdTe film thickness in solar battaries is several micrometers. The left figure shows the microscope photo of CdTe film and the riht figure depicts the scheme of close space chamber. For a conventional CdTe/CdS superstrate cell a CdCl2 annealing treatment is applied which controls the junction
activation, recrystallization, and intermixing of CdS into the CdTe. In a substrate cell the CdCl2 treatment will be applied either only on the CdS or in both layers.
          Polycrystalline CdTe thin films solar cells have shown long term stable performance and high efficiency up to 16.4% under AM 1.5 illumination (small area). If produced in large volume, e.g. more than 60 MW/year, their cost could be lower than 1Euro/W . High specific power (ratio of output power to the weight) solar cells are expected. These features make thin film CdTe solar cells attractive for space applications. It it is important to have a light flexible substrate. The left figure shows CE deposited on polyimide film (8.6% efficiency at AM1.5) and metal foil (~12% efficiency at AM1.5). CdTe solar cells can be grown on very thin Ce02 doped (50-100 mm) space quality cover glass. Solar cells of 10 to 15% have the potential to yield specific power of up to 3 kW/kg. Measurements have shown that CdTe solar cells are stable against proton and electron irradiation. only for a high proton fluence (1013 cm-2) a minor degradation has been measured. These results confirm that CdTe thin film solar cells have a good perspective not only for terrastial but space application. The right figure showd I-V curve for SC on polyimide and glass substrate.