In this work we present an easy to apply method for the in-line energy monitoring of ion implantation in semiconductor industry. The method is based on the light induced generation of electron-hole pairs in silicon semiconductors due to the internal photoelectric effect. Herein, the generation rate of electron-hole pairs decreases with increasing depth. Therefore, the position of the depletion layer, where electrons and holes are separated in a pn junction, has a strong influence on generated photocurrents. The photocurrents were extracted from the I-V curve of illuminated wafers. We used silicon wafers of low n-type doping as raw material. In a Design of Experiments (DoE) a p-type dopant was implanted into the raw material with different doses and energies. The experimental results demonstrate that photocurrent measurements are capable of monitoring the acceleration energy of ions in implantation processes.