The Photon Detection System (PDS) of the first two DUNE far detectors (FD1 and FD2) is composed of 6000 and 672 photon detection units respectively, named X-Arapuca, of different size and geometry. The PDS will complement and boost the DUNE LArTPC for the detection of non beam events: the prompt light detection will improve their tagging, and at low energies it will enable the trigger and the calorimetry of the supernova neutrinos. The X-Arapuca unit is an assembly of several components: its Photon Detection Efficiency (PDE) depends both on the design of the assembly and on the grade and the coupling of the individual components. The X-Arapuca PDE is the driver of the Photon Detection System sensitivity, that in turn determines the sensitivity of the DUNE physics reach for the detection of core-collapse supernova within the galaxy and for nucleon decay searches. In this work we present an update of the absolute PDE of the FD1 X-Arapuca baseline design, measured in laboratory: 160 units of this are deployed in the scale 1:20 FD1 prototype hosted in the NP04 cryostat at the CERN neutrino platform. Further we show how to change the baseline design of the FD1 X-Arapuca, allowing to double its PDE. Finally we review a few selected features of the photon collector of the sixteen FD2 X-Arapuca recently deployed for the FD2 scale 1:20 prototype at CERN in the NP02 cryostat, and of the last six units that integrate the latest advancements.