Broadband Circularly Polarized Light Detection via Spin‐Selective Charge Transport in Quantum Dot Photodiodes

spin angular momentum arising from the helical rotation of its electric field vector perpendicular to the propagation direction [5– 9], and is classified into left-handed and right-handed helicities [10–13]. Conventional photodetectors based on silicon or GaAs inherently lack CPL sensitivity, requiring external polarization optics that increase system complexity, enlarge device size, and reduce overall detection efficiency [14]. A conventional approach for realizing CPL-sensitive photodetectors is to employ chiral materials as photoactive layers [5, 7, 15–19], because chiral mate- rials, defined by their mirror asymmetry, intrinsically respond differently to left-handed circularly polarized (LCP) and right- handed circularly polarized (RCP) light through mechanisms such as circular dichroism [20–27]. Extending CPL detection to the near-infrared (NIR) and short- wave infrared (SWIR) regions [28–35] is highly attractive because of advantages such as deep tissue penetration, reduced scatter- ing, and low-energy operation—features highly beneficial for biomedical imaging and low-visibility applications (e.g., night vision) [36–38]. However, progress has been limited by the lack of materials that exhibit both strong chiroptical activity and efficient NIR/SWIR photoresponse (Tables S1 and S2). Chiral perovskites exhibit excellent CPL sensitivity in the UV–vis range but often show limited infrared response [39–41]. Two-photon absorption has also been investigated, yet its reliance on high- intensity and wavelength-specific excitation restricts practical use [42, 43]. Chiral organic materials with NIR activity have been tested, but they often suffer from poor stability and slow response times [28, 44–47]. While chiroptical activity has also been introduced into inorganic quantum dots (QDs), including those with NIR bandgaps, through their surface functionalization with chiral ligands [48–50], their dispersion in polar solvents leads to significant integration challenges with conventional charge transport layers, as polar solvents can dissolve or damage these layers, causing interlayer mixing and loss of interface integrity. This results in substantial difficulties in incorporating chiral-QDs into typical multilayered photodiode architectures. As a result, their use has been largely restricted to low- performance photoconductors or phototransistors, which face severe integration challenges for image-sensor-level architectures [2, 51, 52]. Traditionally, CPL photodetectors have relied on the intrinsic chirality of light-absorbing layers, raising a fundamental question of whether the intrinsic optical chirality of light absorbers is essential for CPL sensitivity. Inspired by recent advances in spin light-emitting diodes (spin-LEDs) [53–55], we propose an alternative strategy by introducing chirality into charge transport layers, offering a practical yet largely unexplored approach for CPL photodetectors. This strategy exploits the chiral-induced spin selectivity (CISS) effect, a quantum phenomenon in which elec- trons transmitted through chiral structures preferentially adopt one spin orientation even without external magnetic fields [56– 60], thereby enabling spin-selective carrier extraction. This offers significant advantages, including simplified device integration, broad material compatibility, and robust CPL sensitivity with various absorbers. Crucially, because this approach does not depend on wavelength-limited optical chirality, it provides a straightforward route to extend CPL detection into the NIR/SWIR regions, where conventional chiral photoactive materials are scarce or inefficient. This concept underpins the present work. Herein, we report broadband CPL-sensitive QD-photodetectors exploiting the CISS effect in chiral-ZnO electron transport layers (ETLs) (Figure 1a). The structural asymmetry of chiral-ZnO nanoparticles enables preferential transmission of spin- polarized carriers while suppressing opposite spins, effectivel