$A$ solar cell is to be fabricated for efficient conversion of solar radiation to emf using material $A$. The solar cell is to be mechanically protected with the help of a coating using material $B$. If the band gap energy of materials $A$ and $B$ are $E_{A}$ and $E_{B}$ respectively,then which of the following choices is optimum for better performance of the solar cell?

• A
  $E_{A}=1.5 \, eV, E_{B}=5 \, eV$
• B
  $E_{A}=1.5 \, eV, E_{B}=1.5 \, eV$
• C
  $E_{A}=3 \, eV, E_{B}=1.5 \, eV$
• D
  $E_{A}=0.5 \, eV, E_{B}=5 \, eV$