Cellulose Nanocrystal/TiO2 Nanotube Composites for Circularly Polarized Light Detection

Circularly polarized light (CPL) detection is important in the field of advanced optoelectronics. Traditionally, CPL detection with optical elements is limited by the challenge of integration. Chiral materials have been investigated for direct CPL detection without complex optical elements. However, chiral structures such as the CPL absorption layer need further investigation owing to the low anisotropy factor (gph). Herein, we demonstrate a composite structure combining chiral cellulose nanocrystals (CNCs) and TiO2 nanotube arrays (TNAs) for CPL detection. This CNC–TNA structure is fabricated by evaporation-induced self-assembly of CNCs on the top of electrochemically anodized TNAs. The excellent ability to distinguish between left-handed CPL (LCPL) and right-handed CPL (RCPL) is achieved using CNC–TNAs as photoelectrodes. Benefitting from the chiral nematic phase of CNCs, which selectively reflect LCPL and transmit RCPL, gph of CNC–TNA photoelectrodes reaches 0.33, indicating a highly effective distinguishability to CPL. CNC–TNA photoelectrodes realize the CPL detection with high gph (0.33), fast response (0.8 s), and cycling stability under time-varying CPL illumination. In addition, they can track the phase difference of elliptically polarized light due to the sensitivity to polarization states. The CNC–TNA composite structure opens up a potential approach for CPL detection.