How can a detector tell whether light is left- or right-handed? In circularly polarized light (CPL), the electric field rotates continuously as the light travels, producing left- and right-handed states that carry photon spin angular momentum information. Harnessing this information requires CPL detectors capable of distinguishing the two handedness states and converting them into readable electrical signals for subsequent information processing. Conventional CPL detectors rely on bulky and complex external optical components, such as linear polarizers and quarter-wave plates. These components restrict device integration and miniaturization.
Chiral organic semiconductors can discriminate CPL directly. Their molecular structures can be readily tailored, while their solution processability and intrinsic flexibility are advantageous for integrated and flexible devices. However, their development faces an intrinsic trade-off between charge carrier mobility and absorption dissymmetry factor. Considerable efforts have been devoted to resolving this contradiction, contributing to the development of chiral organic semiconductors and thereby CPL detectors.
Hence, writing in Science Bulletin, Cuiyun Liu, Ziyi Xie, Qingbin Li and Huanli Dong from the Institute of Chemistry, Chinese Academy of Sciences, timely review recent progress in chiral organic semiconductors and CPL detectors. The review focuses on the planarity-helicity dilemma and spectral tailoring within chiral organic semiconductors, device engineering and emerging applications.
Balancing chirality and charge transport
The charge carrier mobility and the absorption dissymmetry factor are crucial parameters for evaluating the performance of chiral organic semiconductors for CPL detection. Charge carrier mobility determines how efficiently photogenerated carriers are transported and extracted. The absorption dissymmetry factor reflects the material's intrinsic ability to distinguish left- and right-handed CPL. The two properties are difficult to improve simultaneously. Molecular structures that strengthen chiroptical responses often disrupt the ordered π-π stacking needed for efficient charge transport. Considerable effort has been devoted aiming at resolving this challenge. As for material innovation, recent progress on backbone and side-chain engineering which integrate chiral motifs with π-conjugated frameworks are reviewed. Chiral induction and spontaneous chiral symmetry breaking which generate chiroptical responses in achiral semiconductors are also reviewed. Across these strategies, molecular structure and intermolecular interactions govern chirality transfer and amplification, while also influencing the formation of charge transport pathways.
Tailoring the spectral response
For a photodetector, its spectral response determines which applications it can serve. The review describes how π-conjugation, heteroatom incorporation and donor-acceptor architectures regulate the bandgap. Supramolecular assembly and multicomponent blending provide additional control over optical absorption and chiroptical response. These approaches have extended the response region of chiral organic semiconductors from the ultraviolet through the visible and into the near-infrared, reflecting the structural tunability of organic semiconductors and provides a material basis for CPL detectors with application-oriented spectral responses.
Turning optical differences into electrical signals
A material's intrinsic chiroptical response does not automatically produce an equally strong electrical difference between left- and right-handed CPL. Device engineering controls how light is distributed in the active layer and how photogenerated carriers are separated, transported and collected. Two-terminal devices can use active-layer thickness, optical interference, interface design and applied bias to tune their response. Three-terminal devices add gate-voltage modulation and can amplify weak signals through photogating, threshold-voltage shifts and subthreshold operation. Organic electrochemical transistors further use ion-electron coupling to enable low-voltage detection and light-stimulated synaptic behavior. Across the studies surveyed in the review, current CPL detectors achieve a photocurrent dissymmetry factor of up to 1.67 and a specific detectivity of up to 1016 Jones. Improved detector performance has enabled demonstrations of circularly polarized imaging, information encoding, and neuromorphic computing.
Perspectives
Material systems combining high carrier mobility and high absorption dissymmetry factor remain limited, particularly for polymers, constraining the development of solution-processable CPL detectors and flexible applications. Moreover, their spectral response is largely confined to the visible region, with UV, NIR, and broadband materials still scarce. The mechanisms behind electrical response dissymmetry are not yet fully understood, and chiral assemblies and interfaces remain sensitive to processing conditions and defects. The review therefore calls for CPL selectivity, carrier transport, dark current and response dynamics to be optimized within a unified material-device framework.
