## 4 Conclusions  
The morphological and optical properties of the glass templates nanostructured by A-IPL at increasing ion fluences and in presence of a Ti adhesion layer have been investigated by means of AFM microscopy and by an integrating sphere setup. From the morphological point of view, the possibility to tune the vertical heights (RMS roughness) and the lateral size (lateral correlation length) of the nano-pattern has been explored either (i) by increasing the total ion fluence, in order to increase the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Substrate** & \(\boldsymbol{J_{\text{SC-EQE}}}\) **(mA/cm\({}^{2}\))** & \(\boldsymbol{V_{\text{OC}}}\) **(mV)** & **FF (\%)** & \(\boldsymbol{\eta}\) **(\%)** & \(\mid R_{\text{i}}-R_{\text{FLAT}}\mid/R_{\text{FLAT}}\) \\ \hline Flat & 11.1 & 896 & 60.5 & 6.0 & - \\
0 min & 13.1 & 742 & 50.4 & 4.9 & 50\% \\
2 min & 13.5 & 833 & 53.9 & 6.1 & 40\% \\
4 min & 11.8 & 887 & 52.8 & 5.5 & 2\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Photovoltaic parameters and relative variation of integrated reflectance of co-deposited a-Si:H solar cells grown on flat glass plus pristine and treated nanostructured glass (2 min and 4 min normal incidence IBS). size of the nanostructures; or (ii) by introducing a thin Ti adhesion layer at the Au/glass interface during the A-IPL nanostructuring process. The presence of a Ti layer is effective for the survival of the small scale nanostructures, endowed with a high aspect ratio, during the projection of the pattern through the stencil mask. The main physical mechanism behind this observation has to do with the inhibition of dewetting of the Au film when it decomposes into an array of laterally separated nanowires. The dewetting process is further enhanced by the hyperthermal energy deposition following ion impacts which favor uphill mass transport of Au and increased exposure of the glass substrate to harsh ion etching. In the presence of Ti instead, the pattern of the Au nanowire stencil mask inhibits coarsening of the glass structures as long as the metal nanowires are present during the A-IPL process. In this way, the Ti stabilized Au NWs stencil mask allows us to preserve glass structures with small lateral size below the light diffraction limit, and the refractive index of neighboring media can be gradually matched featuring bio-mimetic moth-eye effect [31]. A relative reduction of about 20% \(\div\) 25% in total integrated reflectance was measured on nanostructured borosilicate glasses treated with the Ti adhesion layer at low ion fluences. On the other hand, in view of enhanced light trapping in photovoltaic applications, a trade-off between antireflection and light scattering (haze) properties has to be found, thus favoring the adoption of nanostructured glasses prepared without a Ti layer. The photon harvesting potential of the nanostructured glass has been tested for different preparation conditions by fabricating thin film amorphous Si solar cells. Enhancement of the short circuit current density against a flat reference cell has been demonstrated for all the devices, especially in the long wavelength range due to light trapping effects. A relative \(I_{\mathrm{SC}}\) increase up to 25% has been measured. The best results have been obtained with substrates prepared at intermediate ion fluence. In this case, morphologies were endowed with relatively large lateral dimensions for improved light trapping, but still moderate RMS roughness, in order to avoid severe electrical deterioration caused by formation of morphology-induced defective regions in the active layer. Finally, a promising approach for improving the electrical performance of the cells has been presented: normal incidence Ar\({}^{+}\) ion sputtering allows us to tailor the morphology of the textured interface within minutes, reducing the width of the local slope distribution and modifying the V-shaped grooves into broad U-shaped valleys.