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 (CHCOONH) to passivate the tin dioxide (SnO) surface. The CHCOONH treatment facilitates SnO oxygen vacancy passivation via interactions between CHCOO groups and Sn cations. Simultaneously, perovskite defects are effectively mitigated by the combination of CHCOO with uncoordinated Pb 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 SnO layer effectively minimizes nonradiative recombination losses. Benefiting from these merits, C-PSC devices with CHCOONH-passivated SnO 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.