[Seany (OP)]

How to they absorb the light/sun-ray energy and transfer it into electrical energy?

[daveshorts]

A solar cell is basically a diode - a one way valve for electricity. So electrons can't flow from the -ve side to the positive one, or at least they can't unless you give an electron a whole lot of energy eg by hitting it with a photon. Then the only way the electron can get back is by flowing all the way around the circuit doing some work in the process.