Multisite Molecular Coordination for Defect and Structural Regulation in Carbon‐Cathode Hole‐Transport‐Layer‐Free CsPbI ₂ Br Solar Cells

ABSTRACT Carbon‐cathode hole‐transport‐layer‐free (HTL‐free) CsPbI ₂ Br solar cells offer a promising route toward high‐performance‐to‐cost photovoltaics, yet their performance is largely constrained by defect‐related losses. Here, a molecular strategy based on terpyridine derivatives is developed to regulate defect states, lattice distortion, and interfacial charge‐transfer energetics in CsPbI ₂ Br films. Owing to cooperative N/O coordination, [2,2′:6′,2″‐terpyridine]‐6,6″‐dicarboxylic interacts with undercoordinated metal ions (Pb ²⁺ /Sn ⁴⁺ ) and vacancy defect sites (I/O) at defect‐rich surfaces, grain boundaries, and buried CsPbI ₂ Br/SnO ₂ interfaces. This coordination‐assisted regulation is associated with improved film crystallinity, reduced electronic non‐uniformity, and more efficient interfacial charge extraction. As a result, carbon‐cathode HTL‐free CsPbI ₂ Br devices achieve a leading comprehensive performance with a power conversion efficiency of 16.02%, minimal hysteresis, improved operational stability, and exceptional reproducibility. Furthermore, the applicability of this molecular approach is demonstrated in MAPbI ₃ ‐based devices, highlighting its potential as a general strategy for defect regulation in the related optoelectronic devices.