Low‐Temperature Crystallized and Flexible 1D/3D Perovskite Heterostructure with Robust Flexibility and High EQE‐Bandwidth Product

Abstract All‐inorganic perovskite cesium lead triiodide (CsPbI 3 ) has attracted much attention among the perovskite family due to its excellent optoelectronic properties and chemical stability. However, the high‐temperature crystallization process makes CsPbI 3 less compatible with commercially flexible substrates, limiting its application into flexible optoelectronics. Here, a cation of 1‐(3‐aminopropyl)‐2pyrrolidinone (APP) is reported that can form 1D (APP)PbI 3 perovskite as templates, and significantly reduce the CsPbI 3 black‐phase transition energy with a low annealing temperature of 75 °C, which further enables a flexible (APP)PbI 3 /γ‐CsPbI 3 (1D/3D) heterostructure photodetector on ITO/PET substrate. A high external quantum efficiency (EQE) greater than 2377% is observed along the orientated 1D/3D heterostructure. The high gain and low noise result in a high specific detectivity (D*) over 10 12 Jones under −0.6 V low bias. The optimized device structure brings a high EQE × bandwidth product of 119 kHz under a low driving bias. Due to the high toughness of orientated APP + ions and the face‐connected [PbI 3 ] − chains structure as a strong energy absorber, the flexible photodetector also shows excellent phase stability and impressive flexibility, remaining >90% initial responsivity after over 20 000 times bending with potential flexible imaging application in harsh environments.