This work deals with the enhancement of the quantum efficiency and photovoltaic energy conversion efficiency of a P-N semiconducting cell by optimizing the dimensions of the cell. Based on the Shockley-Read statistics a general expression for the quantum efficiency of monochromatic incident radiant energy photons has been derived in terms of the absorption coefficient of the incident photons, the minority carrier diffusion length, the built-in electrostatic field appearing in diffused cells and the surface recombination velocity in the exposed layer of the cell. Although the expressions derived may be used for all semiconducting P-N cells, special efforts have been made in the analysis and the computations of the Germanium P-N cell. The Germanium cells show a great potential for photovoltaic energy conversion from radiant energy sources other than the sun. The results for Germanium indicate that the quantum efficiency strongly depends upon the thicknesses of the exposed and base layers. The built-in electrostatic field and the surface recombination velocity in the exposed layer influence the quantum efficiency greatly. Optimization studies for the thicknesses of the exposed ane base layers of a N-P type Germanium for different values of minority carrier diffusion length, built-in electrostatic field and surface recombination velocity have been worked out.