4. Conclusion

Provided that major national research programs maintain the necessary long-term commitment, we can foresee five good reasons why thin-film technologies will be preferred for mass production:

• materials with a direct band gap (chalcogenides, amorphous silicon) absorb ten times more visible light than crystalline silicon;

• for better spectral conversion, it's easier to stack two or three different materials in a thin-film photovoltaic cell, with the front diode converting the blue part of the spectrum delivering the highest voltage ( V _oc " 1,00 V for E _g " 1.70 eV) and the rear diode converting the red part with a lower voltage ( V _oc " 0.60 V for E _g...