Modeling and optimizing the energy conversion efficiency of photovoltaic cells based on semiconductors such as Silicon (Si) or Gallium Arsenide (GaAs) is one of the challenges and issues of scientific research. This book gives an analytical and numerical study of a photovoltaic cell for calculating current densities and estimating their energy conversion efficiency. This study allows us to access the various electrical and physical parameters which characterize the phenomenon of electrical conduction, such as the short-circuit current, the open-circuit voltage, the lifetime of the minority carriers, the surface recombination velocity, doping, etc...