Spacer Engineering of Diammonium‐Based 2D Perovskites toward Efficient and Stable 2D/3D Heterostructure Perovskite Solar Cells

Perovskite solar cells (PSCs) based on 2D/3D heterostructures show great potential to combine the advantages of the high efficiency of 3D perovskites and the high stability of 2D perovskites. However, an in‐depth understanding of the organic‐spacer effects on the 2D quantum well (QW) structures and electronic properties at the 2D/3D interfaces is yet to be fully achieved, especially in the case of 2D perovskites based on diammonium spacers/ligands. Here, a series of diammonium spacers is considered for the construct ion 2D/3D perovskite heterostructures. It is found that the chemical structure and concentration of the spacers can dramatically affect the characteristics of the 2D capping layers, including their phase purity and orientation. Density functional theory calculations indicate that the spacer modifications can induce shifts in the energy‐level alignments at the 2D/3D interfaces and therefore influence the charge‐transfer characteristics. The strong intermolecular interactions between the 2,2‐(ethylenedioxy)bis(ethylammonium) (EDBE) cations and inorganic [PbI6]4− slabs facilitate a controlled deposition of a phase‐pure QW structure (n = 1) with a horizontal orientation, which leads to better surface passivation and carrier extraction. These benefits endow the EDBE‐based 2D/3D devices with a high power conversion efficiency of 22.6% and remarkable environmental stability, highlighting the promise of spacer‐chemistry design for high‐performance 2D/3D PSCs.