Multisite Molecular Coordination for Defect and Structural Regulation in Carbon-Cathode Hole-Transport-Layer-Free...

Carbon-cathode hole-transport-layer-free (HTL-free) CsPbI₂Br 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 CsPbI₂Br films. Owing to cooperative N/O coordination, [2,2':6',2″-terpyridine]-6,6″-dicarboxylic interacts with undercoordinated metal ions (Pb²⁺/Sn⁴⁺) and vacancy defect sites (I/O) at defect-rich surfaces, grain boundaries, and buried CsPbI₂Br/SnO₂ 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 CsPbI₂Br 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 MAPbI₃-based devices, highlighting its potential as a general strategy for defect regulation in the related optoelectronic devices.