title: Improvement of Stability for Small Molecule Organic Solar Cells by Suppressing the Trap Mediated Recombination.
abstract: To understand the degradation mechanism of organic solar cells (OSCs), the charge dynamics of conventional and inverted planar heterojunction OSCs based on boron subthalocyanine chloride (SubPc) and fullerene (C60) with identical buffers during the air exposure were investigated. The results of light intensity dependent open circuit voltage show that the bimolecular recombination is dominated in the fresh devices, regardless of the device structure. The appearance of transient peak in photocurrent after turn-on and the light intensity independent turn-off traces in transient photocurrent suggest that the rapid degradation of conventional device is due to the energy loss originated from the aggravated trap mediated recombination. In contrast, the half-lifetime of inverted device is ∼25 times longer than the conventional one. The improvement of stability is ascribed to the decrease of the trap generation possibility and the suppression of trap mediated recombination in the case of inverted structure, where the penetration of oxygen and water through buffer layer is avoided.
authors.affiliation: Institute of Applied Physics, University of Tsukuba , Tsukuba, Ibaraki 305-8573, Japan.
authors.forename: Xia
authors.initials: X
authors.lastname: Hao
authors.affiliation: Institute of Applied Physics, University of Tsukuba , Tsukuba, Ibaraki 305-8573, Japan.
authors.forename: Shenghao
authors.initials: S
authors.lastname: Wang
authors.affiliation: Institute of Applied Physics, University of Tsukuba , Tsukuba, Ibaraki 305-8573, Japan.|PRESTO, Japan Science and Technology Agency (JST) , Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Takeaki
authors.initials: T
authors.lastname: Sakurai
authors.affiliation: Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo , Komaba, Meguro, Tokyo 153-8902, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Masuda
authors.affiliation: Institute of Applied Physics, University of Tsukuba , Tsukuba, Ibaraki 305-8573, Japan.
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Akimoto
keywords: charge dynamics; organic solar cells (OSCs); recombination; stability; transient photocurrent (TPC)