Cation-π/π-π Synergy Induced Self-Assembly of Semiconductor Spacers for High Efficiency and Stable 2D/3D Perovskite Solar Cells.

2D/3D perovskite heterojunctions exhibit simultaneous improvement of efficiency and stability to meet commercial applications. However, dielectric confinement and an intrinsically uncontrollable crystallization process in 2D perovskites typically lead to large exciton binding energies and poor film quality, hindering charge dissociation, carrier transport, and ultimately device performance. Here, a strong aromatic conjugated ammonium salt spacer (PyPAI) that can spontaneously form self-assembled columnar stacks via synergistic cation-π and π-π interactions is introduced, thereby simultaneously regulating crystal growth and enhancing charge transfer for high performance perovskite solar cells (PSCs). The in situ generated 2D perovskite phases effectively modulate nucleation and crystallization kinetics, yielding superior films with vertically oriented crystals and reduced grain boundary density. Concurrently, the robust aromatic π-conjugated network establishes continuous energy bands, enabling highly efficient carrier shuttling between the inorganic Pb-I framework and the cationic organic layers. Consequently, PyPAI-optimized PSCs achieve a remarkable PCE of 26.41% with superior environmental and operational stability.