The spatial collection efficiencyC(z) is the probability that a photon absorbed at the pointzin the cell will yield a charge carrier into the current. TheCfunction is obtained from the spectral response by means of the inverse Laplace transformation. It gives important information on the cell parameters such as diffusion length, junction depth, surface recombination velocity, etc. Examples ofc‐Si and thin‐film CdS/CdTe cells are given. ©1995 American Institute of Physics.