In a photovoltaic solar module, temperature and shading variations or non uniform illumination but also any recombination of interconnection failure, cell failure are at the origin of local hot spots, variations in the photocurrent or mismatches from cell to another cell, aging and local deterioration of the modules with damages that can be irreversible. To analyze the intrinsic origin and the behavior of the damage phenomena with electrical and thermal stresses, a Deep Level Transient Spectroscopy, DLTS, spectrometer based on a double box-car system is used to characterize the parameters of PV modules under external stressed parameters. Thus, based on DLTS spectroscopy measurements, this, work discusses and analyzes the nature of defects present in PV solar modules. We performed series of experimental measurements after various reverse currents injected for stress, at various temperature in monocrystalline silicon commercial modules. To avoid additional contribution of the photovurrent, electrical and thermal stresses were created in dark into the solar module structure and DLTS measurements were performed before and after in dark conditions for several common periods. Experimental results and analysis point the relation between the parameters of defect obtained by DLTS measurements and the electrical parameters of PV module i.e. the increase of the diffusion current, the low value of shunt resistance and the high value of the ideality factor (A>1). The optimum results that can be achieved with the DLTS technique in the characterization of PV modules were discussed based on previous results published on stressed PV modules obtained by more classical methods. As confirmed by DLTS, originally used for this kind of characterisation, the main results show the huge influence of the working external conditions of PV solar modules in real conditions. This contribution points also the limitation of the DLTS technique for the characterization of complex electronic systems as PV panels