title: On the origin of the open-circuit voltage of polymer-fullerene solar cells.
abstract: The increasing amount of research on solution-processable, organic donor-acceptor bulk heterojunction photovoltaic systems, based on blends of conjugated polymers and fullerenes has resulted in devices with an overall power-conversion efficiency of 6%. For the best devices, absorbed photon-to-electron quantum efficiencies approaching 100% have been shown. Besides the produced current, the overall efficiency depends critically on the generated photovoltage. Therefore, understanding and optimization of the open-circuit voltage (Voc) of organic solar cells is of high importance. Here, we demonstrate that charge-transfer absorption and emission are shown to be related to each other and Voc in accordance with the assumptions of the detailed balance and quasi-equilibrium theory. We underline the importance of the weak ground-state interaction between the polymer and the fullerene and we confirm that Voc is determined by the formation of these states. Our work further suggests alternative pathways to improve Voc of donor-acceptor devices.
authors.affiliation: IMEC-IMOMEC, vzw, Institute for Materials Research, Hasselt University, Wetenschapspark 1, 3590 Diepenbeek, Belgium. koen.vandewal@uhasselt.be
authors.forename: Koen
authors.initials: K
authors.lastname: Vandewal
authors.forename: Kristofer
authors.initials: K
authors.lastname: Tvingstedt
authors.forename: Abay
authors.initials: A
authors.lastname: Gadisa
authors.forename: Olle
authors.initials: O
authors.lastname: Inganäs
authors.forename: Jean V
authors.initials: JV
authors.lastname: Manca
mesh_terms: D004563:Electrochemistry; D037741:Fullerenes / Q000737:chemistry*; D009930:Organic Chemicals / Q000737:chemistry; D010777:Photochemistry; D011108:Polymers / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D037741:Fullerenes; D009930:Organic Chemicals; D011108:Polymers