wavelength energy?

Question

can I make 750nm/3.1eV=400nm1.65ev if I slow down the speed of light in a meduim

h/c=E for 750nm

example ; 700nm/2.89eV=400nm/1.65eV

this is for to get greater energy from a solar cell
or to absorp more wavelengths of energy

i got an improvement of 20% of energy from my 6v 50mAH
cell.

Answer 1

we usually use frequency to calculate the energy of radiation .
you can use wavelenght just as well. However Radiation energy is a flux of rays . so to have any meaning You need to know the power of the radiation falling on a surface area.