Flexible piezoelectric energy harvesters have drawn attention for their potential use as power sources for wearable electronics. However, the harnessed energy cannot be directly connected to load systems. Power conditioning circuits are extremely needed to achieve conditioned and rectified signals. However, there is still no complete overview available, which exhaustively describes and classify the existing AC-DC rectifiers for flexible piezoelectric energy harvesting (F-PEH). In this paper, different rectifiers were investigated, compared, and evaluated. The strengths and limitations of the interfaces were addressed based on the results obtained. These show that for nanocomposite based F-PEH, the parallel Synchronized Switch Harvesting on Inductor (P-SSHI) resonant rectification technique delivers better performance than the full bridge, voltage doubler and CMOS rectifiers by increasing the electromechanical conversion as well as the power extraction efficiency by 200 % than the standard single-phase full bridge rectifier which has a more stable output than the half wave voltage doubler.