Enhanced photodetecting performance in Dion-Jacobson BDA(EA)₂Pb₃Br₁₀ perovskite films via acetate ionic liquid

Photodetectors play pivotal roles in various fields, such as industrial inspection, consumer electronics, autonomous driving. Self-powered photodetectors have the advantage of no external power requirement, which can be used in low-energy optoelectronic fields. Recently, metal halide perovskites have emerged as ideal materials for high-performance photodetection due to their low-cost solution processability, low-temperature fabrication compatibility, and tunable optoelectronic properties. Among various perovskite architectures, two-dimensional (2D) layered perovskites have garnered significant attention for their enhanced environmental stability compared to traditional three-dimensional (3D) perovskites. Generally, 2D perovskites can be classified into Ruddlesden-Popper (RP, L2An–1MnX3n+1) and Dion-Jacobson (DJ, L′An–1MnX3n+1) phases, where L is mono ammonium cations; L′ is diammonium cations; A is small cations such as MA+; M is Pb2+, Sn2+, or Ge2+; X is halide; and n is the number of inorganic layers formed by [MX6]4– octahedron between two long chains. Notably, DJ-type perovskites exhibit distinct structural merits. The diammonium cations (L′) form robust hydrogen bonds with adjacent inorganic layers, which can enhance moisture resistance and facilitate efficient vertical carrier transport. These attributes position DJ-type perovskites as compelling candidates for advancing photodetector technologies. Limited research has been conducted on the practical application of DJ-type perovskites in photodetection, thereby necessitating more in-depth investigations to explore their full potential.Perovskite films are promising candidates for photodetector applications due to their facile fabrication, tunable band gaps, and compatibility with array integration. While one-step spin-coating enables convenient deposition, uncontrolled crystallization during solution processing often results in poor film quality, limiting device performance. This challenge is particularly acute in DJ-type perovskites, where rigid organic molecules disrupt ordered lattice growth, amplifying lattice distortion and residual stress accumulation. To address these issues, strategies such as mixed organic cations, solvent engineering, and additive engineering have been explored. Much research has demonstrated that ionic liquids (ILs) can effectively modulate the crystallization of perovskite thin films through coordination interactions with precursor species. However, the influence of ILs on crystal growth behavior and photodetecting performance in DJ-type perovskites, along with the underlying microscopic mechanisms, remains poorly understood. Further investigation into these aspects is critical for optimizing film morphology and advancing DJ-type-perovskite-based photodetector technologies.In this work, we introduce ethylammonium acetate (EAAc) as an additive to modulate the crystallization of BDA(EA)2Pb3Br10 perovskite films. The acetate anion (Ac–), leveraging its strong coordination affinity for Pb2+, strategically interacts with lead centers to form the intermediate phase, thereby retarding the nucleation rate of perovskite grains during film deposition. Subsequent thermal annealing facilitates a ligand exchange process, where Ac– is gradually displaced by bromide ions (Br–), accompanied by controlled evaporation of the acetate species. Simultaneously, the crystals initiate a reorientation and growth process along the evaporation direction of Ac–, ultimately yielding a compact film characterized by enhanced crystallinity and superior vertical alignment. Further, self-powered photodetectors based on ITO/PEDOT:PSS/BDA(EA)2Pb3Br10/PC71BM/Ag are fabricated, demonstrating exceptional photodetection capabilities. Under monochromatic illumination (340 nm, 646 μW cm–2), the device achieved a photocurrent of 1.54 × 10–6 A and an on/off ratio exceeding 104. Spectral response analysis revealed a peak detectivity (D*) of 5.1 × 1012 Jones at 420 nm, accompanied by a responsivity (R) of 160 mA W–1. These metrics surpass those of many conventional DJ-type-perovskite-based detectors, underscoring the efficacy of the additive engineering strategy. This work not only advances the fundamental understanding of additive-mediated crystallization in 2D perovskites but also provides a scalable approach to fabricating DJ-type perovskite films with excellent optoelectronic properties. The achieved performance metrics and morphological control lay a critical foundation for integrating DJ-type perovskites into a large-area photodetector array.