## 4 Conclusions  
The paper reports the preparation and characterization of nanostructured electrodes based on vertically-aligned Cu NWs subsequently covered by CdTe thin films for potential use in \"substrate\"-type solar cells relying on A\({}^{\mathrm{II}}\)-\(\mathrm{B}\)VI chalcogenide compounds. The Cu NWs matrix was obtained through template-assisted electrodeposition within the nanopores of a supported AAO template, while the CdTe thin films were obtained through VTE, RF-MS, and ECD techniques. SEM morphological examination of the Cu NW array revealed its densely-packed nature (\(\sim\)32.5%) and the geometrical features of the NWs, i.e., the center-to-center distance of \(\sim\)150 nm and an aspect-ratio around 4 (tailored for retaining the NWs' vertical orientation on the substrate after the AAO host removal step). The morphological, structural, and optical properties of CdTe thin films obtained through VTE, RF-MS, and ECD were studied and analyzed to determine the optimal experimental conditions that could allow a good degree of CdTe penetrability through the Cu NWs array. A comparative critical discussion of the obtained data points out that the evaporated CdTe thin film exhibits excellent crystallinity, with a pronounced (111) crystalline orientation, although with larger CdTe crystallites (\(\sim\)81 nm) that generally prevent CdTe protrusion through the Cu NWs. Similar results were observed for the sputtered CdTe thin film, although slightly improved due to a smaller crystallite size of \(\sim\)64 nm. However, the crystallite size of \(\sim\)21 nm for the electrodeposited CdTe film rendered the ECD approach most suitable for properly filling the gaps through the Cu NWs array. An overall observed reduction in the evaluated CdTe deposition rate among the three methods investigated(i.e., \(\sim\)700 nm/min for VTE, \(\sim\)70 nm/min for RF-MS and \(\sim\)7 nm/min for ECD), as well as the reduction of the crystallite size, seem to favor the better protrusion of the CdTe through the Cu NWs. Ultimately, the computed optical band gap energies of the CdTe thin films prepared by the three investigated methods are in the range of 1.43-1.48 eV, approaching thus the reported values for bulk CdTe films (1.51 eV). The results obtained from all investigations show that the ECD method may be a suitable technique for use in producing robust absorber layer/collecting back-electrode nanostructured interfaces relying on CdTe-embedded Cu NWs. Although further optimization of the ECD process parameters may be required to achieve a CdTe thin film with competitive compositional and structural properties, the electrochemical method could represent a cost-effective solution when engaged in the fabrication of solar cells based on A\({}^{\text{II}}\)-B\({}^{\text{VI}}\) heterojunctions; vertically-aligned NWs could be designed to improve the charge collection towards the electrodes, contributing to a better efficiency of the cells. To the best of our knowledge, no such detailed comparative study has yet been reported. Conceptualization, V.-A.A.; methodology, S.A. and V.-A.A.; validation, S.A., M.P.S. and V.-A.A.; formal analysis, A.-M.P., I.A., C.L., S.I., S.A., L.P., M.P.S. and V.-A.A.; investigation, A.-M.P., I.A., C.L. and S.I. ; resources, S.A., L.P. and V.-A.A.; writing-original draft preparation, A.-M.P. ; writing-review and editing, A.-M.P., C.L., S.I., A.M.P.S. and V.-A.A.; supervision, S.A. and V.-A.A.; project administration, S.A. and V.-A.A.; funding acquisition, I.A., S.I., S.A., L.P., M.P.S. and V.-A.A. All authors have read and agreed to the published version of the manuscript. This research was funded by the \"Executive Unit for Financing Higher Education, Research, Development and Innovation\"--UEFISCDI (Romania) through the grants: 195/2020 (PN-III-P1-1-1-PD-2019-0466), 25/2020 (PN-III-P1-1.1-TE-2019-0846) and 115/2020 (PN-III-P1-1.1-TE-2019-0868), as well as by the \"Fonds de la Recherche Scientifique\" --FNRS (Belgium). Not applicable.