Protective substrate for a device that collects or emits radiation

1. A protective substrate for a device comprising at least one element that collects or emits radiation, the substrate comprising a transparent polymer layer and a barrier layer on at least one face of the polymer layer, characterized in that the barrier layer consists of an antireflection multilayer of at least two thin transparent layers having both alternately lower and higher refractive indices and alternately lower and higher densities to provide a constituent multilayer, each thin layer of the constituent multilayer of the barrier layer being an oxide, nitride or oxynitride layer, wherein the two thin layers comprise a junction zone having a density gradient between the density of the two thin layers at an interface between the two thin layers, wherein the thickness of the junction zone is between 10 nm to 30 nm.

2. The substrate according to claim 1 , characterized in that a difference between the density of a higher density layer and the density of a lower density layer of each pair of successive thin layers of the constituent multilayer of the barrier layer is greater than or equal to 10% of the density of the lower density layer.

3. The substrate according to claim 1 , characterized in that a geometric thickness of each thin layer of the constituent multilayer of the barrier layer is adapted in order to maximize a transmission of radiation through the substrate to or from the element that collects or emits radiation.

4. The substrate according to claim 1 , characterized in that the substrate comprises the barrier layer on the face of the polymer layer intended to be facing the element that collects or emits radiation and/or the barrier layer on the face of the polymer layer intended to be facing the other way from the element that collects or emits radiation.

5. The substrate according to claim 1 , characterized in that, for each pair of successive thin layers of the constituent multilayer of the barrier layer, the two successive thin layers comprise the same chemical elements, the chemical elements of the two successive thin layers having different stoichiometries.

6. The substrate according to claim 5 , characterized in that the constituent multilayer of the barrier layer comprises at least a superposition of a thin hydrogenated silicon nitride layer having a refractive index between 1.8 and 1.9 at 550 nm and of a thin hydrogenated silicon nitride layer having a refractive index between 1.7 and 1.8 at 550 nm.

7. The substrate according to claim 1 , characterized in that, for each pair of successive thin layers of the constituent multilayer of the barrier layer, the two successive thin layers comprise different chemical elements to form two successive thin layers of different chemical compositions.

8. A device that collects or emits radiation comprising a protective substrate, the substrate comprising a transparent polymer layer and a barrier layer on at least one face of the polymer layer, characterized in that the barrier layer consists of an antireflection multilayer of at least two thin transparent layers having both alternately lower and higher refractive indices and alternately lower and higher densities to provide a constituent multilayer, each thin layer of the constituent multilayer of the barrier layer being an oxide, nitride or oxynitride layer, wherein the two thin layers comprise a junction zone having a density gradient between the density of the two thin layers at an interface between the two thin layers, wherein the thickness of the junction zone is between 10 nm to 30 nm; and at least one element that collects or emits radiation, the element being arranged relative to the substrate so as to be capable of collecting radiation that passes through the polymer layer and the barrier layer, or of emitting radiation through the polymer layer and the barrier layer.

9. The device according to claim 8 , characterized in that the element that collects or emits radiation is a photovoltaic cell or an organic light-emitting diode.

10. A process for manufacturing a protective substrate for a device, the protective substrate comprising at least one element that collects or emits radiation, the substrate comprising a transparent polymer layer and a barrier layer on at least one face of the polymer layer, characterized in that the barrier layer consists of an antireflection multilayer of at least two thin transparent layers having both alternately lower and higher refractive indices and alternately lower and higher densities to provide a constituent multilayer, each thin layer of the constituent multilayer of the barrier layer being an oxide, nitride or oxynitride layer, wherein the two thin layers comprise a junction zone having a density gradient between the density of the two thin layers at an interface between the two thin layers, wherein the thickness of the junction zone is between 10 nm to 30 nm, wherein the process is characterized in that at least some of the thin layers of the constituent multilayer of the barrier layer are deposited by plasma-enhanced chemical vapor deposition (PECVD) and/or by sputtering.

11. The manufacturing process according to claim 10 , characterized in that at least some of the thin layers of the constituent multilayer of the barrier layer are deposited by plasma-enhanced chemical vapor deposition (PECVD) by varying, during the deposition, the pressure in the deposition chamber and/or the power and/or the relative proportions of the precursors and/or the nature of the precursors.

12. The manufacturing process according to claim 10 , characterized in that at least some of the thin layers of the constituent multilayer of the barrier layer are deposited by reactive sputtering by varying, during the deposition, the pressure in the deposition chamber and/or the power and/or the nature of the reactive gas.

13. The manufacturing process according to claim 10 , characterized in that, prior to the deposition of the thin layers of the constituent multilayer of the barrier layer on one face of the polymer layer, said face of the polymer layer is activated by means of a plasma.