Do you know how a solar panel actually works? The way of exploiting the energy stored in photons is quite spectacular; seemingly simple, but very complicated in a microscopic level.
The effect of a photovoltaic cell is not even close to a hundred per cent, more like sixteen to twenty. There is still lots of work to be done! The dream scenario is reaching a hundred per cent. Whether it´s physically possible is another matter... I know scientists have reached fifty in laboratories here in Norway, so we´ll get closer every day. I´m positive we´ll find even better ways of extracting the energy from sun rays in the future!