This chapter contains sections titled: Effect of Light on the Depletion Layer of the Semiconductor–Electrolyte Junction The Fate of Photogenerated Carriers Magnitude of the Photocurrent Gartner Model for Photocurrent Carrier Recombination A Mathematical Treatment for the Lifetime of Carriers Effect of Illumination on Fermi Level-Quasi Fermi Level Solar Cell Performance Current–Voltage Characteristics of a Solar Cell The Equivalent Circuit of a Solar Cell Solar Cell Efficiency Ohmic Contact Defects in Solids Summary