Flexible Black-Phase CsPbI ₃ Photodetectors Enabled by Low-Temperature Processing via BA ₂ MA ₂ Pb ₃ I ₁₀ Structural Templating

The high energy barrier for the δ phase to black phase CsPbI₃ transition necessitates annealing above 180 °C, preventing low-temperature processing and integration on flexible substrates. We demonstrate a novel approach for synthesizing γ-CsPbI₃ films at 100 °C using BA₂MA₂Pb₃I₁₀ 2D perovskite as a tailored growth template. In situ photoluminescence (PL) analysis of the thin-film formation kinetics reveals that the BA₂MA₂Pb₃I₁₀ template effectively lowers the formation energy barrier of γ-CsPbI₃, enabling its low-temperature phase transformation. Comparative studies using alternative 2D perovskites possessing distinct lattice parameters confirm that only lattice-matched crystalline structures can serve as effective templates, promoting the low-temperature epitaxial growth and phase transition of γ-CsPbI₃. Utilizing this templating strategy, γ-CsPbI₃ thin films were successfully integrated as the photosensitive layer into photoconductive detectors fabricated on both rigid and flexible substrates. These devices exhibit promising photodetection capabilities, including responsivity up to 1.06 × 10⁻⁵ A/W and detectivity up to 7.53 × 10⁵ Jones, and demonstrate array-based imaging functionality.