title: Ultrafast charge-transfer reactions of indoline dyes with anchoring alkyl chains of varying length in mesoporous ZnO solar cells.
abstract: Dye-sensitized solar cells based on a mesoporous ZnO substrate were sensitized with the indoline derivatives DN91, DN216 and DN285. The chromophore is the same for each of these dyes. They differ from each other in the length of an alkyl chain, which provides a second anchor to the ZnO surface and prolongs cell lifetime. Ultrafast transient absorption measurements reveal a correlation between the length of the alkyl chain and the fastest electron-injection process. The depopulation of the excited state and the associated emergence of the oxidized molecules are dominant spectral features in the transient absorption of the dyes with shorter alkyl chains. A slower picosecond-scale decay proceeds at constant rate for all three derivatives and is assigned to electron transfer into the trap states of ZnO. All assignments are in good agreement with a higher quantum efficiency of charge injection leading to higher short-circuit currents J(sc) for dyes with shorter alkyl chains.
authors: Laser Research Institute, Stellenbosch University, Private Bag X1, Matieland 7602 (South Africa).
authors: Egmont
authors: E
authors: Rohwer
authors: Iulia
authors: I
authors: Minda
authors: Gabriele
authors: G
authors: Tauscher
authors: Christoph
authors: C
authors: Richter
authors: Hidetoshi
authors: H
authors: Miura
authors: Derck
authors: D
authors: Schlettwein
authors: Heinrich
authors: H
authors: Schwoerer
keywords: dye-sensitized solar cells; indoline dyes; injection rate; pump-probe spectroscopy; zinc oxide