A method for fabricating a photovoltaic device includes applying a diblock copolymer layer on a substrate and removing a first polymer material from the diblock copolymer layer to form a plurality of distributed pores. A pattern forming layer is deposited on a remaining surface of the diblock copolymer layer and in the pores in contact with the substrate. The diblock copolymer layer is lifted off and portions of the pattern forming layer are left in contact with the substrate. The substrate is etched using the pattern forming layer to protect portions of the substrate to form pillars in the substrate such that the pillars provide a radiation absorbing structure in the photovoltaic device.