A transparent diffusive OLED substrate includes the following successive elements or layers: (a) a transparent flat substrate made of mineral glass having a refractive index n1 of between 1.48 and 1.58, (b) a monolayer of mineral particles attached to one side of the substrate by means of a low index mineral binder having a refractive index n2 of between 1.45 and 1.61, and (c) a high index layer made of an enamel having a refractive index n4 between 1.82 and 2.10 covering the monolayer of mineral particles, the mineral particles having a refractive index n3 between n2+0.08 and n4−0.08 and protruding from the low index mineral binder so as to be directly in contact with the high index layer, thereby forming a first diffusive interface between the mineral particles and the low index binder, and a second diffusive interface between the mineral particles and the high index layer.