Enhancing Carrier Mobility in Chiral One-Dimensional Perovskites with Strong Chirality Through Molecular Design of Naphthalenediimide Cations

Chiral hybrid organic-inorganic perovskites have emerged as promising materials for spin-optoelectronic and spintronic devices owing to their excellent spin-polarization properties. By incorporating relatively large chiral organic cations, chiral perovskites can be extended to low-dimensional crystalline phases, bringing unique electronic structures that arise from quantum confinement effects and structural distortions. Compared to chiral two-dimensional (2D) perovskites, chiral one-dimensional (1D) perovskites exhibit stronger octahedral distortion, less orbital overlap, and greater quantum confinement, resulting in higher chirality, larger band gap, but lower charge transport ability. Therefore, designing chiral cations with excellent charge transport ability and strong chirality is highly desired for chiral 1D perovskites. Here, we present a molecular design strategy that utilizes the n-type semiconducting material naphthalenediimide (NDI) as the core of the chiral cations to enhance charge transport while maintaining the strong chirality of chiral 1D perovskites. We synthesized chiral NDI-based cations, namely <i>R</i>-NDIEPAI, by introducing <i>R</i>-propane-1,2-diamine, ethylamine, and iodide ion to the NDI core. The <i>R</i>-NDIEPAI thin film shows a strong absorption peak between 350 - 400 nm (corresponding to the optical band gap of 3.54 - 3.10 eV) and a strong positive CD signal (~3200 mdeg) at 400 nm, indicating the <i>R-</i> chirality is carried to <i>R-</i>NDIEPAI. Moreover, the <i>R</i>-NDIEPAI thin films demonstrate a high degree of crystalline order, characterized by (<i>h</i>00) lamellar peaks in the out-of-plane direction (d₍₁₀₀₎= 19.6 Å) and the (010) π–π stacking peak in the in-plane direction (d₍₀₁₀₎= 4.65 Å). The corresponding 1D chiral perovskite (<i>R</i>-NDIEPA)PbI₃ thin films annealed at 200 °C show a strong exciton peak at 410 nm, which is comparable to conventional 1D perovskites. Importantly, the CD spectrum shows a CD signal of ~450 mdge corresponding to the exciton peak, demonstrating that the chirality is transferred from the <i>R</i>-NDIEPA⁺ cations into the 1D inorganic chains. Based on the HOMO and LUMO levels of <i>R</i>-NDIEPA⁺ determined by cyclic voltammetry, the (<i>R</i>-NDIEPA)PbI₃ exhibits a type II band energy alignment. This type II band energy alignment between the organic and inorganic motifs results in a significant quenching of the photoluminescence of (<i>R</i>-NDIEPA)PbI₃ compared to that of <i>R</i>-NDIEPAI thin films, indicating an efficient charge separation at the interface of the [PbI₆]^4-inorganic chain and the <i>R</i>-NDIEPA⁺ organic layer. The carrier mobility of 1D chiral (<i>R</i>-NDIEPA)PbI₃ perovskites will be studied through the space charge-limited current measurement of hole-only and electron-only devices to futher investigate their electronic properties.