polymers Article Investigation of Dye Dopant Inﬂuence on Electrooptical and Morphology Properties of Polymeric Acceptor Matrix Dedicated for Ternary Organic Solar Cells Gabriela Lewi ´ nska 1, * , Piotr Jele ´ n 2 , Jaroslaw Kanak 1 , Lukasz Walczak 3 , Robert Socha 4 , Maciej Sitarz 2 , Jerzy Sanetra † and Konstanty Waldemar Marszalek 1   Citation: Lewi ´ nska, G.; Jele ´ n, P.; Kanak, J.; Walczak, L.; Socha, R.; Sitarz, M.; Sanetra, J.; Marszalek, K.W. Investigation of Dye Dopant Inﬂuence on Electrooptical and Morphology Properties of Polymeric Acceptor Matrix Dedicated for Ternary Organic Solar Cells. Polymers 2021, 13, 4099. https://doi.org/ 10.3390/polym13234099 Academic Editor: Rong-Ho Lee Received: 20 October 2021 Accepted: 22 November 2021 Published: 25 November 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁl- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Faculty of Computer Science, Electronics and Telecommunication, AGH University of Science and Technology, 30 Mickiewicza Ave., 30059 Krakow, Poland; kanak@agh.edu.pl (J.K.); marszale@agh.edu.pl (K.W.M.) 2 Department of Silicate Chemistry and Macromolecular Compounds, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, 30059 Krakow, Poland; pjelen@agh.edu.pl (P.J.); msitarz@agh.edu.pl (M.S.) 3 Science & Research Division, PREVAC sp. z o.o., Raciborska 61, 44362 Rogow, Poland; lukasz.walczak@prevac.pl 4 Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30239 Krakow, Poland; robert.socha@ikifp.edu.pl * Correspondence: glewinska@agh.edu.pl; Tel.: +48-692-376-639 † The author Jerzy Sanetra is retired; jsanetra@agh.edu.pl. Abstract: The publication presents the results of investigations of the inﬂuence of dye dopant on the electrooptical and morphology properties of a polymeric donor:acceptor mixture. Ternary thin ﬁlms (polymer:dye:fullerene) were investigated for potential application as an active layer in organic solar cells. The aim of the research is to determine the effect of selected dye materials (dye D131, dye D149, dye D205, dye D358) on the three-component layer and their potential usefulness as an additional donor in ternary cells, based on P3HT donor and PC71BM acceptor. UV–vis spectroscopy studies were performed, and absorption and luminescence spectra were determined. Ellipsometry parameters for single dye and ternary layers have been measured. The analyses were performed using the Raman spectroscopy method, and the Raman spectra of the mixtures and single components have been determined. Organic layers were prepared and studied using scanning electron microscope and atomic force microscope. For dyes, ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy studies were carried out and the ternary system was presented and analyzed in terms of energy bands. Keywords: dye; organic solar cells; ellipsometry; ternary organic ﬁlms; morphology examination 1. Introduction Organic photovoltaics (OPV) has been developing in recent years due to its cost, solu- tion processibility, semi-transparency, mechanical ﬂexibility, light weight, and has become increasingly interesting for technology [1–3]. The possibility of application in wearable systems, connection to IOT (Internet of Things) and powering personal devices [4–6] as well as the hope for the use of organic cells in space [7], causes substantial popularity of the organic photovoltaic. It should also be mentioned the possibility of using OPV in indoor applications, which have excellent potential for use in ﬂexible and wearable electronics [8–10]. One of the rising trends in organic photovoltaics are ternary solar cells. In ternary solar cells [11], a suitably selected third component (additional donor or additional acceptor) is introduced into the active layer to increase cell efﬁciency. The mixture (donor 1:donor 2:acceptor blend) forms a bulk heterostructure and in the photo- voltaic process, and photons are absorbed. Materials that broaden the absorption spectrum and facilitate the transport of holes and electrons are selected as the third element [12]. Polymers 2021, 13, 4099. https://doi.org/10.3390/polym13234099 https://www.mdpi.com/journal/polymers