Unsymmetric Squaraine For Narrow Band Green-Selective Organic Photodetectors

Narrowband color-selective photodetectors have drawn considerable attention due to their extensive applications in optical communication or sensing. Because of the 7C-7C interaction between molecules in the film state, color-selective materials with narrowband absorption in solution state could not always construct narrowband color-selective devices. Here, a new green-light selective narrowband material, unsymmetric 4-(3,5-dimethyl-2Hpyrrol-1-ium-2-ylidene)-2-(diphenylamino)squaraine (UPSQ), is reported. This unsymmetric squaraine, with donor-acceptor-donor structure, could be solution processed, and the device with solution-processed single sensitive layer shows considerable green light selectivity with peak at 500 nm. Meanwhile, due to the stereo hindrance effect of diphenylamine group, the intermolecular interaction in the film is significantly reduced. From the EQE curve, the FWHM of the device is found to be only 90 nm and the maximum of EQE is about 16% at the bias of-3 V. The promising performance of the device indicates that the stereo-hindrance effect is of use in fabricating narrowband devices and the strategy of adjusting sensitive wavelength by changing substituent group in the donor-acceptor-donor structure is worth promoting.