Low‐Dimensional Metal Halide‐Organic Interdigitated p/n Heterojunction Solar Cells Enabled by Thiomorpholine Hydroiodide Additive

ABSTRACT Low‐dimensional metal halides are attractive p‐type absorbers for stable photovoltaics, yet constructing efficient interdigitated p/n heterojunctions is limited by poor phase control, high defects and interfacial losses. Herein, we report a synergistic molecular and topographical engineering strategy to address these challenges. Thiomorpholine hydroiodide (TMI) is introduced to regulate the crystallization kinetics and passivate defects of the two‐dimensional p‐type metal halide absorber. Through hydrogen‐bonding/electrostatic interactions and interaction‐induced electronic redistribution involving PbI 2 , TMI promotes preferred orientation, phase purity and reduced trap density. Consequently, TMI‐mediated optimization delivers progressive efficiency improvements across systematically advanced device structures. The efficiency has been raised from 20.99% to 22.14% in single p‐type metal halide devices, and from 22.44% to 23.45% in planar p/n heterojunctions upon integrating a ternary organic n‐layer. Crucially, utilizing the TMI‐optimized absorber as a template for high‐fidelity nanoimprinting to construct the target interdigitated p/n heterojunction yields a champion efficiency of 24.27%, which is the record value in low‐dimensional metal halide‐based solar cells so far. The optimized interdigitated device without encapsulation also retains 84% of its initial efficiency after 1000 h of continuous maximum power point tracking. This work provides a scalable pathway for high‐efficiency, stable structured photovoltaics.