Current commercial solar cells have incredibly low efficiency, with a commercial maximum of usually 15-30%. The energies of light that most conventional materials (e.g. silicon) can absorb does not match the energy of the solar radiation that falls upon it.
It is classically difficult - as you'll soon see - to calculate ground state + excited states for larger molecules.
VQE is a combination of classical and quantum algorithms so that it is extremely accurate, and takes much less time when compared to a pure classical algorithm.
We are simulating compounds used for solar cells, and modelling what wavelengths of solar radiation they can store.