Ultranarrow Bandwidth Organic Photodiodes by Exchange Narrowing in Merocyanine H- and J-Aggregate Excitonic Systems

Ultranarrowband organic photodiodes (OPDs) are demonstrated for thin film solid state materials composed of tightly packed dipolar merocyanine dyes. For these dyes the packing arrangement can be controlled by the bulkiness of the donor substituent, leading to either strong H- or strong J-type exciton coupling in the interesting blue (H-aggregate) and NIR (J-aggregate) spectral ranges. Both bands are shown to arise from one single exciton band according to fluorescence measurements and are not just a mere consequence of different polymorphs within the same thin film. By fabrication of organic thin-film transistors, these dyes are demonstrated to exhibit hole transport behavior in spin-coated thin films. Moreover, when used as organic photodiodes in planar heterojunctions with C-60 fullerene, they show wavelength-selective photocurrents in the solid state with maximum external quantum efficiencies of up to 11% and ultranarrow bandwidths down to 30 nm. Thereby, narrowing the linewidths of optoelectronic functional materials by exciton coupling provides a powerful approach to produce ultranarrowband organic photodiodes.