title: Improved efficiency of bulk heterojunction hybrid solar cells by utilizing CdSe quantum dot-graphene nanocomposites.
abstract: We present a significant efficiency enhancement of hybrid bulk heterojunction solar cells by utilizing CdSe quantum dots attached to reduced graphene oxide (rGO) as the electron accepting phase, blended with the PCPDTBT polymer. The quantum dot attachment to rGO was achieved following a self-assembly approach, recently developed, using thiolated reduced graphene oxide (TrGO) to form a TrGO-CdSe nanocomposite. Therefore, we are able to obtain TrGO-CdSe quantum dot/PCPDTBT bulk-heterojunction hybrid solar cells with power conversion efficiencies of up to 4.2%, compared with up to 3% for CdSe quantum dot/PCPDTBT devices. The improvement is mainly due to an increase of the open-circuit voltage from 0.55 V to 0.72 V. We found evidence for a significant change in the heterojunction donor-acceptor blend nanomorphology, observable by a more vertical alignment of the TrGO-quantum dot nanocomposites in the z-direction and a different nanophase separation in the x-y direction compared to the quantum dot only containing device. Moreover, an improved charge extraction and trap state reduction were observed for TrGO containing hybrid solar cells.
authors.affiliation: Freiburg Materials Research Center (FMF), University of Freiburg, Stefan-Meier-Straße 21, D-79104 Freiburg, Germany. Michael.Krueger@fmf.uni-freiburg.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Eck
authors.forename: Chuyen Van
authors.initials: CV
authors.lastname: Pham
authors.forename: Simon
authors.initials: S
authors.lastname: Züfle
authors.forename: Martin
authors.initials: M
authors.lastname: Neukom
authors.forename: Martin
authors.initials: M
authors.lastname: Sessler
authors.forename: Dorothea
authors.initials: D
authors.lastname: Scheunemann
authors.forename: Emre
authors.initials: E
authors.lastname: Erdem
authors.forename: Stefan
authors.initials: S
authors.lastname: Weber
authors.forename: Holger
authors.initials: H
authors.lastname: Borchert
authors.forename: Beat
authors.initials: B
authors.lastname: Ruhstaller
authors.forename: Michael
authors.initials: M
authors.lastname: Krüger