Weak-Light Detectivity of Phototransistors from the Defect Passivation of Perovskite Floating Gates Utilizing Branched Carbohydrate–Siloxane Triblock Copolymers

Abstract

Photodetectors are essential optoelectronic components for biotechnological sensing and optical communication systems. Perovskite materials, owing to their broad spectral absorption, high charge-carrier mobility, mechanical flexibility, and solution processability, have emerged as promising candidates for next-generation photodetection. In this work, a block copolymer composed of polydimethylsiloxane (PDMS) and maltotriose is introduced as an interfacial modifier to regulate the crystallographic, morphological, and optoelectronic properties of perovskite thin films, thereby enhancing phototransistor performance, particularly under weak-light conditions. Copolymers with different architectures exhibit distinct surface energies, enabling efficient charge transfer between perovskite polycrystalline grains and hydroxy-rich carbohydrate segments, which effectively shortens exciton lifetimes and suppresses recombination. Notably, perovskite phototransistors incorporating a two-armed branched PDMS-block-maltotriose achieve the highest device performance under 455 nm illumination. Even at an ultralow light intensity of 0.20 μW cm^–2, the device exhibits a responsivity of 0.37 A W^–1 and a detectivity of 4.0 × 10⁹ Jones, demonstrating excellent sensitivity. This performance enhancement is attributed to PDMS-directed microphase separation that spatially accommodates perovskite nanocrystals within the carbohydrate matrix, where abundant hydroxy groups passivate surface defects through hydrogen bonding or Pb²⁺ coordination. These results highlight the potential of block-copolymer/perovskite nanohybrids for high-performance weak-light phototransistors.