To analyze the dynamic of ion species through a MAPbI3-xClx (HaP) solar cell, an operando hard X-ray photoelectron spectroscopy (HAXPES) study was proposed. Stacked Au/Ag/AZO/PCBM/HaP/NiO/ITO/glass structures, where AZO, PCBM, NiO, and ITO stand for Al-doped zinc oxide, phenyl-C61-butyric acid methyl ester, nickel oxide, and indium tin oxide, respectively, were evaluated. Experimental core level analysis under an applied bias voltage highlighted that a certain threshold voltage (above the open-circuit voltage (VOC)) is required to trigger the iodide (I-) migration from the HaP to the adjacent electron and hole transport layers. Study also demonstrated that the diffusion of I- in AZO/PCBM over time is unidirectional and follows the gradient descent in concentration. We observed that the irreversibility of the I- transport leads to the absorption of I- by the Ag layer to form a silver iodide (AgI) compound. Furthermore, this work also pointed out the efficiency of an ITO layer when deposited between Ag and AZO to serve as the ion diffusion barrier layer. Finally, the results demonstrated that the presence of ITO restrains the AgI formation and contributes to improving cell performances.