Solar batteries convert light energy into electricity. This is done by taking light and splitting it into electrons and holes (holes are like anti-electrons). These electrons and holes are separated in an electrical circuit, and this leads to the flow of current.

In the 1950s, it was discovered that a high number of free electrons could be formed when light was shined on a silicon wafer. By "capturing" these electrons, the researchers were able to convert this into an electrical current. This is known as a photovoltaic (light - electricity) cell.The photovoltaic effect was actually known about(using different materials) much earlier than this, with the first observation of this effect in the mid-1800s. However, the types of solar cells made with these other materials could only achieve an efficiency of about 1%. The significance of the work in the 1950s was that photovoltaic cells using silicon were demonstrated to have an efficiency of about 6%. I think the best present day photovoltaic cells operate at around 15% or maybe a little bit more.

On a side note, Albert Einstein won the Nobel Prize for his work that he published in 1904 on the photoelectric effect.