Subject: Is it possible to change the energy level of a photon?

In my studies about light and solar energy, I have come across the fact that 
solar cells are only 15-25% effective in utilizing sunlight because they need 
to be hit with photons of a certain range of energy levels. Any photon that has 
a higher or lower energy level than this required range does not have any 
effect on the solar celll. If these photons could be somehow homogenized into 
ones with the right energy levels, then a lot more solar energy can be 
processed by solar cells. Thus, I wish to know if it is possible to change 
photon energy levels, whether by shearing off energy from a photon that has too 
much energy, or by merging together two weak photons to produce an acceptable 
photon.

Re: Is it possible to change the energy level of a photon?