Currently, photovoltaics has become an established industrial field with the global installed capacity over 500 GWp and with a perspective of reaching the terawatt installed capacity within the following decade. The field is dominated by silicon wafer-based cells for which previously unforeseen low system prices have been reached. The advantages of photovoltaics based on silicon thin film (lower consumption of energy-costly silicon and thus shorter energy payback time) have not been sufficient to overcome the disadvantage of lower efficiencies (12 % record efficiency vs. ~25 %). Thus, the development and production of silicon thin film photovoltaics has nearly stopped. The other types of thin film-based PV (CdTe, CIS) struggle as well.
Yet, the highest recent efficiencies have been achieved by merging both technologies : Si wafers for photogeneration and thin films for selective passivated contacting scheme. The record efficiency  reached 26.7 % by using silicon heterojunction (SHJ) cells with interdigitated back contacts composed of intrinsic and either n or p-type hydrogenated amorphous silicon layers with thicknesses of ~ 10 nm. Many variations of solar cells with carrier-selective passivation contacts (e.g. TOPCON or POLO) are also being explored.
The record SHJ cell above has been fabricated by photolithography, unsuitable for mass production. Thus, simpler stencil mask-based technology is being developed in the NextBase H2020 project . The tunnel-IBC approach further simplifies the process by eliminating the patterning and aligning the hole collector contacts.
Assay of the back-contacting scheme with n and p fingers brings new challenges on how to measure these very thin layers, in particular, when deposited on textured wafers. We will review the principle and use of optical profilometry  based on the attenuation of the Raman scattering from the underlying wafer which allowed us to map the layers with a thickness resolution better than 0.5 nm. The optical profilometry also finds its use in other new ways of interface engineering by inserting 2D materials  or self-assembled dipolar molecule monolayers. [6,7].
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 K. Yoshikawa, H. Kawasaki, W. Yoshida, T. Irie, K. Konishi, K. Nakano, T. Uto, D. Adachi, M. Kanematsu, H. Uzu, K. Yamamoto, Silicon heterojunction solar cell with interdigitated back contacts for a photoconversion efficiency over 26%, Nat. Energy. 2 (2017) 17032.
 NextBase, Web. (2016). http://nextbase-project.eu/ (accessed May 3, 2019).
 M. Ledinský, B. Paviet-Salomon, A. Vetushka, J. Geissbühler, A. Tomasi, M. Despeisse, S.D. Wolf, C. Ballif, A. Fejfar, Profilometry of thin films on rough substrates by Raman spectroscopy, Sci. Rep. 6 (2016) 37859.
 Z. Hájková, M. Ledinský, A. Vetushka, J. Stuchlík, M. Müller, A. Fejfar, M. Bouša, M. Kalbáč, O. Frank, Photovoltaic characterization of graphene/silicon Schottky junctions from local and macroscopic perspectives, Chem. Phys. Lett. 676 (2017) 82–88.
 A. Vetushka, L. Bernard, O. Guseva, Z. Bastl, J. Plocek, I. Tomandl, A. Fejfar, T. Baše, P. Schmutz, Adsorption of oriented carborane dipoles on a silver surface, Phys. Status Solidi B. (2015).
 M. Hladík, A. Vetushka, A. Fejfar, H. Vázquez, Tuning of the gold work function by carborane films studied using density functional theory, Phys. Chem. Chem. Phys. 21 (2019) 6178–6185.