Near-Infrared Circularly Polarized Light Detection through Chiral Polymer Blends with Enhanced Spin Selectivity

A key challenge for organic photodetectors is achieving circularly polarized light (CPL) detection in the near-infrared (NIR) band, which has promising applications in spectroscopy, imaging, and communications. However, most current methods for achieving this detection, particularly in the NIR range, are complex. In this paper, we present a simple and practicable method by blending chiral polythiophene (P3HT-PPI(D)/P3HT-PPI(L)) and nonchiral random copolymers (CPX). By modulating the copolymerization ratio of random copolymers and the blending ratio with chiral block copolymers, the resulting blended films can successfully induce chirality transfer under intermolecular forces. The circular dichroism (CD) spectra of the blended films were measured up to the NIR region, showing chiral absorption between 200 and 800 nm of wavelength. The addition of conjugated polymers results in an increased degree of aggregation of the system, as demonstrated by magnetic conductive atomic force microscopy (mc-AFM) which exhibits a higher chiral induced spin selectivity (CISS) effect. The CPL detector based on this blended film combines both the favorable charge transport properties of organic semiconductors and the chiral optical response of chiral materials, enabling the differentiated detection of CPL with a wide wavelength range. Furthermore, a device array was fabricated to encrypt the image information. This work is instructive to the chiral transfer mechanism of polymers and will benefit the large-scale integrated implementation of CPL detectors.