STUDIA UBB CHEMIA, LXVIII, 1, 2023 (p. 275-283) (RECOMMENDED CITATION) DOI:10.24193/subbchem.2023.1.20 This work is licensed under a Creative Commons Attribution- NonCommercial-NoDerivatives 4.0 International License. BULK AND BILAYER INVERTED ORGANIC SOLAR CELLS (OSCs) EXHIBITING D-A AND A-D-A DONORS WITH 2,2’-BI[3,2-b]THIENOTHIOPHENE UNITS AND PC61BM OR C70 ACCEPTORS Levi GABRIAN a , Gavril-Ionel GIURGI a,b , Lorant SZOLGA a,b,* , Andreea Petronela CRIȘAN a , Elena BOGDAN a , Ramona GĂLĂTUŞ b , Anamaria TEREC a , Ion GROSU a,* ABSTRACT. Inverted bilayer and inverted bulk heterojunction OSCs were fabricated and investigated using D-A and A-D-A donors with bi[3,2-b]thienothiophene units and PC61BM or C70 acceptors. The cells were optimized by varying the donor/acceptor ratios, the thickness of the layers and the conditions for the spin-coating deposition of the active materials. Keywords: organic solar cells, inverted bilayer structure, inverted bulk heterojunction, 2,2’-bi[3,2-b]thienothiophene donors INTRODUCTION 2,2’-Bi[3,2-b]thienothiophene ([3,2-b]-TT) derivatives show a plethora of applications, in emerging fields as medicinal chemistry, [1-3] non-linear optic devices [4,5], materials with liquid crystal behavior [6,7] and conducting (co)polymers. [8–10]. Due to their special opto-electronic properties they were also employed for the fabrication of efficient OSCs (as building blocks in donor molecules [11–16] or non-fullerene acceptors [17–22]) or dye- sensitized solar cells (DSSCs) [23–26]. The replacing of a thiophene ring or a bithiophene unit either in acceptors (A) (e.g., [18]) or in donors (D) (e.g., [12]) with a [3,2-b]-TT moiety a Babes-Bolyai University, Faculty of Chemistry and Chemical Engineering, Department of Chemistry and SOOMCC, Cluj-Napoca, 11 Arany Janos, 400028, Cluj-Napoca, Romania b Optoelectronics Group, Base of Electronics Department, ETTI, Technical University of Cluj- Napoca, Str. Memorandumului, Nr.28, Cluj-Napoca, 400114, Romania * Corresponding authors: lorant.szolga@bel.utcluj.ro; ion.grosu@ubbcluj.ro ©2023 STUDIA UBB CHEMIA. Published by Babeş-Bolyai University.