Aromatic spacer engineering for 2D halide perovskites and their application in solar cells

Perovskites have emerged as a promising new generation of photovoltaic conversion materials, gradually surpassing traditional silicon-based materials in solar cell research. This development is primarily due to their superior power-conversion efficiency (PCE), simple fabrication process, and cost-effective production. However, the low stability of perovskite ionic crystals poses a significant challenge to their stability, hindering the progress of perovskite materials and devices. Although two-dimensional (2D) perovskites offer improved stability, adding organic amine ions results in a quantum confinement effect that reduces the optoelectronic performance of devices. To counter this issue, the strategic design of suitable spacer cations offers a potential solution. Aromatic amine ions possess greater polarity and structural adjustability compared to aliphatic amine ions, making them advantageous in mitigating the quantum confinement effect. This review focuses on phenylethylammonium (PEA) as a representative aromatic spacer cation. It categorizes the evolution of these cations into four trajectories: alkyl chain modification, substitution of hydrogen atoms on the aromatic ring with specific substituents, replacement of benzene rings with aromatic heterocycles, and utilization of multiple aromatic rings instead of a monoaromatic ring. The structure, properties, and corresponding device performance of aromatic spacer cations utilized in reported 2D perovskites are discussed, followed by the presentation of a series of factors for selecting and designing aromatic amine ions for future development.