## 1 Introduction  
Thin film solar cell technologies, with the limited physical thickness of the light absorber, suffer from ineffective absorbance of near-bandgap light. To increase the photocurrent and then the power conversion efficiency, light harvesting strategies have to be introduced in order to trap the light in the active region while minimizing reflection and parasitic absorption. Based on the significant prospective benefits of reduced thickness, such as lower production costs and feasibility of materials with lower carrier diffusion length, the design of efficient light-management concepts is achieving more and more importance [1; 2; 3; 4]. Both more mature technologies and the emerging families of polymer and perovskite solar cells can gain from the implementation of such strategies [5; 6; 7; 8; 9]. The need for light trapping is vital for the amorphous silicon based cells, both because of the weak absorption coefficient and for the limitations on the feasible thickness, due to the relatively poor electronic quality of the materials which calls for a drift-based p-i-n design [10]. Thanks to its maturity, this technology is thus often used as a platform for testing advanced approaches aimed at improving light management [3]. Here, a self-organized method for fabricating and tailoring nanostructured glasses to be applied as substrates promoting photon harvesting is presented and thin film silicon solar cells are once again used as the test-bed. For thin film Si solar cells, the highest efficiencies have been so far reached with light-trapping schemes based on randomly textured interfaces combined with a reflective back contact. A common approach consists in the use of a rough front electrode made of textured transparent conductive oxide (TCO). Structuring of the supporting glass is also being pursued with nano-fabrication techniques such as nanoimprint lithography, where the desired morphology is reproduced into a UV-curable transparent resin [11]. Self-organized methods are an interesting alternative for patterning the substrates. As demonstrated in several seminal works [12; 13; 14], low-energy ion beam sputtering (IBS) has good potential as a single-step and fast processing route to produce large-area (size tunable), self-organized nanoscale patterned surfaces compatible with the present semiconductor industry. Ion irradiation of a self-organized metal nanowire (NW) stencil mask allows the projection of its morphological features into the supporting substrates which can be either amorphous, like glass [15], or crystalline, as GaAs and Silicon [16; 17]. In the latter approach, high aspect ratio nanostructures are formed on the substrates as a consequence of the lower ion erosion rate of metal (e.g., gold) nanowires with respect to the substrate material. In order to further enhance the vertical amplification of transferred nanostructures, we developed an upgraded version of the process where the metal stencil mask lifetime is prolonged by co-evaporation of metallic atoms during ion irradiation (assisted-ion projection lithography, A-IPL) [18]. The high aspect ratio features confer broadband anti-reflection functionality to the textured glass substrate and at the same time ensure a high efficiency for diffuse scattering (high haze) [19; 20]. We here pursued the goal of improving the tunability of the optical properties relying on the ability to control the morphological features of the pattern transferred from the metal stencil mask. To this purpose, the sacrificial mask has to be well-engineered and its morphological features have to be stable even under ion bombardment at high temperature (during A-IPL), where the gold is subjected to dewetting processes that can introduce disorder into the transferred pattern. In the present work, we demonstrate that we can separately optimize the pattern either for anti-reflective purpose or for high haze functionality by changing the lateral size of the nanostructures and their vertical scale in a controlled way.