Amorphous diamond-line carbon (a:DLC) films are suitable for use as a protective layer and/or anti-reflecting coating for silicon solar cells. Microhardness tests show a high hardness of about 4700 kg mm(-2) Optical measurements in the visible light on a silicon solar cell without anti-reflecting coating where a:DLC was deposited as an anti-reflecting (AR) coating, show a significant reduction in the reflection of the light of about 25-45% as compared with the reflection from the solar cell before deposition of the a:DLC film. The current-voltage (I-V) characteristics of solar cells without an anti-reflecting coating and with a:DLC as the AR coating layer show an improvement in the short circuit current (from 107 mA to 116 mA) and in the efficiency of the cell by 1% (from 8% to 9%). I-V characteristics of a solar cell with AR coating and deposited a:DLC (400 Angstrom thickness) over that film as a protective coating, show a slight reduction of the short circuit current (from 168 mA to 145 mA), and the efficiency of the solar cell decreases (16% to 14%). However, the microhardness was significantly increased.