We propose a simple and non-destructive method to access the properties of the defects within the subcells of multijunction solar cells (MJSC) based on the extension of two well-known techniques, namely Admittance Spectroscopy (AS) and Deep-Level Transient Spectroscopy (DLTS). Due to the electrical coupling between the subcells of an MJSC, the AS and DLTS signatures of the defects present in the subcells are difficult to identify and to properly analyse, and other independent phenomena could be misinterpreted as such. From numerical simulations and theoretical developments, it is shown how the use of dedicated experimental conditions, in particular specific light biases, on MJSCs can reveal the signatures of the defects present in each subcell and allow one to analyse them without misinterpretation.