{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T20:40:05Z","timestamp":1788295205518,"version":"build-2803163510"},"reference-count":34,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,5,1]],"date-time":"2026-05-01T00:00:00Z","timestamp":1777593600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100008530","name":"European Regional Development Fund","doi-asserted-by":"crossref","award":["BG16RFPR002-1.014-0006"],"award-info":[{"award-number":["BG16RFPR002-1.014-0006"]}],"id":[{"id":"10.13039\/501100008530","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>Organic-type solar cells containing an active layer of block copolymer donor PTB7-Fx (x = 0, 20, and 100), based on benzo [1,2-b:4,5-b\u2019]dithiophene and variably fluorinated thieno [3,4-b]thiophene units, and fullerene acceptor [6,6]phenyl-C71-methylbutyrate, were constructed. The active layer thin film of the solar cells was obtained from a dichlorobenzene solution at an established concentration via spin-coating of the donor\u2013acceptor mixture in the presence of solvent additives such as 3% diiodooctane and 1% triethyl phosphate. Organic photovoltaic elements with normal device architecture were prepared on glass substrates using an indium tin oxide anode, a spin-coated hole transporting layer of poly(ethylene dioxythiophene):polystyrenesulfonate, the aforementioned active layer, followed by an electron transporting layer of zinc oxide nanoparticles, and finally a magnetron sputtered silver (Ag) top-electrode. The optical properties, thin film morphology, and the thickness of the active layers were investigated. Additionally, current density\u2013voltage characteristics and impedance spectra of photovoltaic devices were measured. It was found that PTB7-Fx:PC71BM-based solar cells processed in the presence of two types of solvent additives, diiodooctane and triethyl phosphate, with a sputtered Ag top-electrode display similar absorption and quantum efficiency spectra, as well as comparable current density\u2013voltage characteristics and efficiencies to the same devices fabricated without additives. The diiodooctane solvent additive preferably dissolves the fullerene component and has a positive effect on fill factor enhancement, impedance spectra improvement, and amelioration in charge carrier transport and collection, whereas the triethyl phosphate solvent additive preferentially dissolves the copolymer donor and has a more pronounced impact on the refined morphology of the thin film active layers.<\/jats:p>","DOI":"10.3390\/ijms27094064","type":"journal-article","created":{"date-parts":[[2026,5,1]],"date-time":"2026-05-01T09:33:17Z","timestamp":1777627997000},"page":"4064","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Solar Cells Based on PTB7-Fx: PC71BM Active Layer Processed with Two Types of Solvent Additives and Sputtered Ag Top-Electrode"],"prefix":"10.3390","volume":"27","author":[{"given":"Georgy","family":"Grancharov","sequence":"first","affiliation":[{"name":"Institute of Polymers, Bulgarian Academy of Sciences, Acad. G. Bontchev Str. Bl. 103A, 1113 Sofia, Bulgaria"},{"name":"National Centre of Excellence Mechatronics and Clean Technologies, 8 Blvd. Kliment Ohridski, 1756 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rositsa","family":"Gergova","sequence":"additional","affiliation":[{"name":"Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Georgi","family":"Popkirov","sequence":"additional","affiliation":[{"name":"Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hristosko","family":"Dikov","sequence":"additional","affiliation":[{"name":"Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2558-2898","authenticated-orcid":false,"given":"Marushka","family":"Sendova-Vassileva","sequence":"additional","affiliation":[{"name":"Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia, Bulgaria"},{"name":"Center of Competence of Mechatronics and Clean Technologies\u2014MIRACle, \u201cAcad. G. Bontchev\u201d Str. 4, 1113 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,5,1]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1832","DOI":"10.1016\/j.progpolymsci.2013.09.005","article-title":"Designing pi-conjugated polymers for organic electronics","volume":"38","author":"Guo","year":"2013","journal-title":"Prog. Polym. Sci."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"34","DOI":"10.1016\/j.orgel.2015.01.014","article-title":"Solution-processable polymeric solar cells: A review on materials, strategies and cell architectures to overcome 10%","volume":"19","author":"Etxebarria","year":"2015","journal-title":"Org. Electron."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Leo, K. (2017). Elementary processes in organic photovoltaics. 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