title: Size-Tuning of WSe2Flakes for High Efficiency Inverted Organic Solar Cells.
abstract: The development of large-scale production methods of two-dimensional (2D) crystals, with on-demand control of the area and thickness, is mandatory to fulfill the potential applications of such materials for photovoltaics. Inverted bulk heterojunction (BHJ) organic solar cell (OSC), which exploits a polymer-fullerene binary blend as the active material, is one potentially important application area for 2D crystals. A large ongoing effort is indeed currently devoted to the introduction of 2D crystals in the binary blend to improve the charge transport properties. While it is expected that the nanoscale domains size of the different components of the blend will significantly impact the performance of the OSC, to date, there is no evidence of quantitative information on the interplay between 2D crystals and fullerene domains size. Here, we demonstrate that by matching the size of WSe2few-layer 2D crystals, produced by liquid-phase exfoliation, with that of the PC71BM fullerene domain in BHJ OSCs, we obtain power conversion efficiencies (PCEs) of ∼9.3%, reaching a 15% improvement with respect to standard binary devices (PCE = 8.10%), i.e., without the addition of WSe2flakes. This is the highest ever reported PCE for 2D material-based OSCs, obtained thanks to the enhanced exciton generation and exciton dissociation at the WSe2-fullerene interface and also electron extraction to the back metal contact as a consequence of a balanced charge carriers mobility. These results push forward the implementation of transition-metal dichalcogenides to boost the performance of BHJ OSCs.
authors.affiliation: Center of Materials Technology and Photonics and Electrical Engineering Department, Technological Educational Institute (TEI) of Crete , Heraklion 71004, Crete, Greece.
authors.forename: George
authors.initials: G
authors.lastname: Kakavelakis
authors.forename: Antonio Esau
authors.initials: AE
authors.lastname: Del Rio Castillo
authors.forename: Vittorio
authors.initials: V
authors.lastname: Pellegrini
authors.forename: Alberto
authors.identifier: 0000-0002-3493-4157
authors.initials: A
authors.lastname: Ansaldo
authors.affiliation: Center of Materials Technology and Photonics and Electrical Engineering Department, Technological Educational Institute (TEI) of Crete , Heraklion 71004, Crete, Greece.
authors.forename: Pavlos
authors.initials: P
authors.lastname: Tzourmpakis
authors.forename: Rosaria
authors.initials: R
authors.lastname: Brescia
authors.forename: Mirko
authors.identifier: 0000-0002-2188-8059
authors.initials: M
authors.lastname: Prato
authors.affiliation: Foundation of Research and Technology (FORTH), Institute of Electronic Structure and Laser (IESL) , Heraklion 71110, Crete, Greece.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Stratakis
authors.affiliation: Center of Materials Technology and Photonics and Electrical Engineering Department, Technological Educational Institute (TEI) of Crete , Heraklion 71004, Crete, Greece.
authors.forename: Emmanuel
authors.identifier: 0000-0003-0257-1192
authors.initials: E
authors.lastname: Kymakis
authors.forename: Francesco
authors.identifier: 0000-0001-7238-9420
authors.initials: F
authors.lastname: Bonaccorso
keywords: efficiency enhancement; inverted organic solar cell; liquid-phase exfoliation; sedimentation-based separation; tungsten diselenide