Dual-Functional Ammonium Acetate as a Bilateral Buried Interface Passivator Enabling Efficient and Stable Carbon-Based Hole-Transport-Layer-Free Perovskite Solar Cells

Planar hole-transport-layer (HTL)-free carbon-based perovskite solar cells (C-PSCs) exhibit notable advantages such as low cost and improved environmental compatibility. However, their practical applications are hindered by a relatively low efficiency and poor stability. The establishment of a buried interface architecture can effectively enhance the long-term stability of the C-PSC devices. Nevertheless, defect generation during perovskite formation and associated nonradiative carrier recombination remain challenges. Herein, we introduce a bidirectional coordination strategy utilizing ammonium acetate (CH₃COONH₄) to passivate the tin dioxide (SnO₂) surface. The CH₃COONH₄ treatment facilitates SnO₂ oxygen vacancy passivation via interactions between CH₃COO^- groups and Sn⁴⁺ cations. Simultaneously, perovskite defects are effectively mitigated by the combination of CH₃COO^- with uncoordinated Pb²⁺ and the formation of N-H···I^- hydrogen bonds. These interactions provide a promising foundation for perovskite crystal growth and promote vertical crystallization. Additionally, a favorable buried interface between the perovskite and underlying SnO₂ layer effectively minimizes nonradiative recombination losses. Benefiting from these merits, C-PSC devices with CH₃COONH₄-passivated SnO₂ achieved a maximum PCE of 15.5% and demonstrated exceptional operational stability, exceeding 1000 h under ambient conditions. This synergistic bidirectional coordination strategy provides an effective route for fabricating efficient and durable C-PSC devices.