This text presents the theoretical basis of PV in crystalline silicon in terms of semiconductor physics, device analysis and measurement. Coverage includes a short history of PV, (including reasons as to why the broad application been applied before), solar radiation and semiconductor physics, including PN junctions (boundary between p- and n- type semiconductors, having marked rectifying characteristics; used in diodes, photocells). Special emphasis is given to the physical and technological requirements to achieve high efficiency. Additionally, other types of solar cells are discussed...