Semitransparent Layers of Social Self-Sorting Merocyanine Dyes for Ultranarrow Bandwidth Organic Photodiodes

Two dipolar merocyanines consisting of the same pi-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.

Automated summary

Two dipolar merocyanines with the same chromophore but different alkyl substituents exhibit distinct packing arrangements in their solid state, resulting in ultranarrow absorption bands. Their self-sorting behavior in mixed thin films affects the opto-electronic properties. The tailored two-component material can optimize organic photodiodes with narrow bandwidths and high external quantum efficiency, suitable for applications such as low-power heart rate monitors.