Direct Detection of Circularly Polarized Light Using Chiral Copper Chloride–Carbon Nanotube Heterostructures

Direct Detection of Circularly Polarized Light Using Chiral Copper Chloride−Carbon Nanotube Heterostructures Ji Hao,⊥Haipeng Lu,*,⊥Lingling Mao, Xihan Chen, Matthew C. Beard, and Jeffrey L. Blackburn* Cite This: ACS Nano 2021, 15, 7608−7617 Read Online ACCESS Metrics & More Article Recommendations * sı Supporting Information ABSTRACT: The emergent properties of chiral organic− inorganic hybrid materials offer opportunities in spin-depend- ent optoelectronic devices. One of the most promising applications where spin, charge, and light are strongly coupled is circularly polarized light (CPL) detection. However, the performance of state-of-the-art CPL detectors using chiral hybrid metal halide semiconductors is still limited by the low anisotropy factor, poor conductivity, and limited photo- responsivity. Here, we synthesize 0D chiral copper chloride hybrids, templated by chiral methylbenzylammonium (R/S- MBA), i.e., (R-/S-MBA)2CuCl4, that display circular dichroism for the ligand-to-metal charge transfer transition with an absorption anisotropy factor (gCD) among the largest reported for chiral metal halide semiconductor hybrids. To circumvent the poor conductivity of the unpercolated inorganic framework of this chiral absorber, we develop a direct CPL detector that utilizes a heterojunction between the chiral (MBA)2CuCl4 absorber layer and a semiconducting single-walled carbon nanotube (s-SWCNT) transport channel. Our chiral heterostructure shows high photoresponsivity of 452 A/W, a competitive anisotropy factor (gres) of up to 0.21, a current response in microamperes, and low working voltage down to 0.01 V. Our results clearly demonstrate a useful strategy toward high-performance chiral optoelectronic devices, where a nanoscale heterostructure enables direct CPL detection even for highly insulating chiral materials. KEYWORDS: chiral organic−inorganic hybrid materials, chiral copper chloride, carbon nanotube, circularly polarized light detection, heterojunction, optoelectronics INTRODUCTION Detection of circularly polarized light (CPL) is of great importance for the development of various optical technolo- gies, including optical imaging,1,2 remote sensing,3 quantum computing4,5 and information processing and communica- tion.6,7 Conventional optical detectors require coupling with optical polarizers to detect CPL, which often limits their sensitivity and resolution. In contrast, direct detection of the polarization state of CPL can be achieved in chiral systems that display circular dichroism (CD), i.e., distinct absorption coefficients for left- and right-handed CPL.8−14 The challenge for integrating efficient chiral absorbers into CPL detectors is effectively transducing the optical CD into sufficiently large electrical signals and amplifying the discrimination (anisotropy factor) between the different photon helicities. The development of chiral organic/inorganic metal halide semiconductors (MHS)9,15−18 is a very promising solution to realize the direct detection of CPL19 because of their chiroptical activity and superior optoelectronic properties.20 Additionally, charge transport in chiral MHS can be highly dependent on the carrier spin sense via the chiral-induced spin- selectivity (CISS) mechanism,17,18,21 thus providing additional tuning parameters to distinguish the polarization state of CPLs (as CPL carries +1> or −1> angular momentum). A series of reports have recently demonstrated direct CPL detection using chiral-MHS. For instance, in 2020, Chen et al.9 and Wang et al.13 separately demonstrated direct CPL photodetectors using 1D and quasi-2D chiral perovskite semiconductors within simple two-terminal electronic device structures. These promising initial demonstrations can still be improved upon, as these architectures require high operating voltages (10−20 V) and produce relatively low output current (∼pA). Very Received: February 5, 2021 Accepted: March 29, 2021 Published: April 6, 2021 Article www.acsnano.org © 2021 American Chemical Society 7608 https://doi.org/10.1021/acsnano.1c01134 ACS Nano 2021, 15, 7608−7617