TY  - JOUR
A1  - Kim, Jin Hong
A1  - Schembri, Tim
A1  - Bialas, David
A1  - Stolte, Matthias
A1  - Würthner, Frank
T1  - Slip‐Stacked J‐Aggregate Materials for Organic Solar Cells and Photodetectors
BT  - This paper is dedicated to Prof. Daoben Zhu on the occasion of his 80th birthday
JF  - Advanced Materials
N2  - Dye–dye interactions affect the optical and electronic properties in organic semiconductor films of light harvesting and detecting optoelectronic applications. This review elaborates how to tailor these properties of organic semiconductors for organic solar cells (OSCs) and organic photodiodes (OPDs). While these devices rely on similar materials, the demands for their optical properties are rather different, the former requiring a broad absorption spectrum spanning from the UV over visible up to the near‐infrared region and the latter an ultra‐narrow absorption spectrum at a specific, targeted wavelength. In order to design organic semiconductors satisfying these demands, fundamental insights on the relationship of optical properties are provided depending on molecular packing arrangement and the resultant electronic coupling thereof. Based on recent advancements in the theoretical understanding of intermolecular interactions between slip‐stacked dyes, distinguishing classical J‐aggregates with predominant long‐range Coulomb coupling from charge transfer (CT)‐mediated or ‐coupled J‐aggregates, whose red‐shifts are primarily governed by short‐range orbital interactions, is suggested. Within this framework, the relationship between aggregate structure and functional properties of representative classes of dye aggregates is analyzed for the most advanced OSCs and wavelength‐selective OPDs, providing important insights into the rational design of thin‐film optoelectronic materials.
KW  - crystal engineering
KW  - exciton coupling
KW  - J‐aggregates
KW  - organic photodiodes
KW  - organic solar cells
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-276537
VL  - 34
IS  - 22
ER  - 
TY  - JOUR
A1  - Schembri, Tim
A1  - Kim, Jin Hong
A1  - Liess, Andreas
A1  - Stepanenko, Vladimir
A1  - Stolte, Matthias
A1  - Würthner, Frank
T1  - Semitransparent Layers of Social Self‐Sorting Merocyanine Dyes for Ultranarrow Bandwidth Organic Photodiodes
JF  - Advanced Optical Materials
N2  - Two dipolar merocyanines consisting of the same π‐conjugated chromophore but different alkyl substituents adopt very different packing arrangements in their respective solid state with either H‐ or J‐type exciton coupling, leading to ultranarrow absorption bands at 477 and 750 nm, respectively, due to exchange narrowing. The social self‐sorting behavior of these push‐pull chromophores in their mixed thin films is evaluated and the impact on morphology as well as opto‐electronical properties is determined. The implementation of this well‐tuned two‐component material with tailored optical features allows to optimize planar heterojunction organic photodiodes with fullerene ​(C\(_{60}\)) with either dual or single wavelength selectivity in the blue and NIR spectral range with ultranarrow bandwidths of only 11 nm (200 cm\(^{-1}\)) and an external quantum efficiency of up to 18% at 754 nm under 0 V bias. The application of these photodiodes as low‐power consuming heart rate monitors is demonstrated by a reflectance‐mode photoplethysmography (PPG) sensor.
KW  - exciton coupling
KW  - merocyanine dyes/pigments
KW  - narrow bandwidth
KW  - organic photodiodes
KW  - social self‐sorting
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-244762
VL  - 9
IS  - 15
ER  - 
TY  - JOUR
A1  - Bialas, David
A1  - Zitzler-Kunkel, André
A1  - Kirchner, Eva
A1  - Schmidt, David
A1  - Würthner, Frank
T1  - Structural and quantum chemical analysis of exciton coupling in homo- and heteroaggregate stacks of merocyanines
JF  - Nature Communications
N2  - Exciton coupling is of fundamental importance and determines functional properties of organic dyes in (opto-)electronic and photovoltaic devices. Here we show that strong exciton coupling is not limited to the situation of equal chromophores as often assumed. Quadruple dye stacks were obtained from two bis(merocyanine) dyes with same or different chromophores, respectively, which dimerize in less-polar solvents resulting in the respective homo- and heteroaggregates. The structures of the quadruple dye stacks were assigned by NMR techniques and unambiguously confirmed by single-crystal X-ray analysis. The heteroaggregate stack formed from the bis(merocyanine) bearing two different chromophores exhibits remarkably different ultraviolet/vis absorption bands compared with those of the homoaggregate of the bis(merocyanine) comprising two identical chromophores. Quantum chemical analysis based on an extension of Kasha’s exciton theory appropriately describes the absorption properties of both types of stacks revealing strong exciton coupling also between different chromophores within the heteroaggregate.
KW  - exciton coupling
KW  - merocyanines
KW  - quantum chemical analysis
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170200
VL  - 7
ER  -