2, Swiss Federal Laboratories for Materials Science and Technology (Empa), Dübendorf, Zurich, Switzerland
The wavelength-selectivity in narrowband photodetectors is an important parameter in color photography, medical imaging, intelligence surveillance and in energy harvesting. Conventional photodetectors have a broadband response beyond the wavelength of interest which hinders their application in visible-opaque, infra-red selectivity or vice-versa. Moreover, it is highly challenging to obtain photodetectors with a full-width at half maximum (FWHM) of less than 100 nm. Here, we show that we can overcome these limitations by tailoring the supramolecular assemblies using organic dyes for photodetection. Strong molecular coupling enhances the absorption coefficient and improves exciton diffusion in these photodetectors. Self-assembly of these organic dyes in solution results in a narrowband J-aggregate with FWHM of around 15 nm. Three individual photodetectors with different wavelength-selectivity at 580, 780 and 1000 nm are demonstrated in this study. Using ink-jet printing, homogeneous thin layers of compact TiO2 (20 nm), mesoporous TiO2 (50 nm) and the active layer are printed and the device was completed by other deposition processes. All these photodetectors show an external quantum efficiency of around 20 % and internal quantum efficiency of more than 90%. A high transparency of around 80% in the visible region for the NIR dyes is achieved in these photodetectors without any anti-reflective coatings.