Chemical bridging in a 2D/3D heterojunction via dual-anchoring functionalized molecules for efficient, stable and flexible perovskite solar cells

Constructing two-dimensional/three-dimensional (2D/3D) perovskite heterojunctions has emerged as an effective interfacial engineering strategy to passivate surface defects, optimize energy-level alignment, and suppress ion migration. However, conventional 2D layers are typically formed by surface stacking of bulky organic cations, which often result in weak interfacial coupling and hinder carrier transport, thereby limiting device performance. In this work, a single-molecule dual-functional surface-passivation strategy is proposed, in which 5-methyltryptamine hydrochloride (Me-TACl) treatment constructs a stable 2D perovskite passivation layer on top of the 3D perovskite films and establishes a chemical bridge between them. This “chemically bridged heterojunction passivation” enhances interfacial coupling, suppresses surface defects, and optimizes energy level alignment. As a result, the Me-TACl-treated devices exhibit remarkable enhancement in photovoltaic performance. The champion device achieves a power conversion efficiency (PCE) of 26.35%, with a stabilized power output (SPO) of 26.20% over 300 s, outperforming the control device (24.67%). Moreover, the flexible device retains 92% of its initial efficiency (24.21%) after bending at a curvature radius of 5 mm for 5000 cycles, demonstrating outstanding mechanical durability. This post-treatment strategy simultaneously enhances efficiency, stability, and flexibility, offering insights for scalable high-efficiency perovskite photovoltaics and a viable interfacial design for next-generation devices.