Multi-site Molecular Regulation Enables Efficient Low-Dimensional Metal Halide/Organic Nano-Interdigitated Heterojunction Solar Cells.

Low-dimensional metal halides offer considerable environmental stability and structural tunability; however, their power conversion efficiencies (PCEs) still lag far behind those of their three-dimensional counterparts. While ordered p-n interdigitated heterojunctions present a highly promising architecture to maximize interfacial charge extraction, implementing this strategy in low-dimensional frameworks is severely impeded by disordered grain growth, high trap densities, and phase heterogeneity. Herein, we introduce bis(carboxymethyl) trithiocarbonate (BMTTC) as a multifunctional bulk additive to address these crystallization-related bottlenecks. Benefiting from its symmetric structure, BMTTC establishes synergistic Lewis acid-base coordination with undercoordinated Pb2+ ions and multi-site hydrogen-bonding networks with organic cations. These dual interactions are suggested to regulate crystallization kinetics and contribute to defect passivation. Consequently, when integrated into ordered low-dimensional metal halide/organic interdigitated heterojunctions, the BMTTC-modified small area (0.09 cm2) device delivers a champion PCE of 24.04% (compared to 22.52% for the control). This molecular regulation strategy also shows scalability, yielding a promising PCE of 23.02% for a 1 cm2 device. Furthermore, the unencapsulated BMTTC-modified device demonstrates improved operational stability under maximum power point tracking. This work provides a facile but effective molecular modulation strategy that synergistically advances the efficiency and operational durability of low-dimensional metal halide photovoltaics.