Strategies for Quasi‐2D Integration in Perovskite p‐i‐n Solar Cells

Until recently, bulky ammonium cations, or 2D cations, one of the most promising avenues for interface passivation, have been applied almost exclusively to the p‐type interface of the n‐i‐p architecture. As the perovskite photovoltaics community gradually moves toward the inverse architecture (p‐i‐n), the question of whether to integrate 3D/2D interfaces at the interface between perovskite and the N‐type contact layer is only natural. By comparing different integration strategies, this work highlights the importance of solvent engineering and additive strategies to integrate quasi‐2D perovskite in p‐i‐n devices. It is demonstrated that these strategies enable almost complete conversion of lead iodide (PbI 2 ) excess through its conversion to quasi‐2D phases, result in a quasi‐Fermi level splitting (QFLS) gain of up to 40 meV, and promote the emergence of quasi‐2D phases of higher dimensions, which are less detrimental to electron extraction. Increasing device efficiency and stability using 2D cations, however, remains a challenge for the p‐i‐n architecture due to the quasi‐2D phases’ intrinsic properties and interfacial mechanical stress at the nanoscale. It is anticipated that, to take full advantage of quasi‐2D perovskites’ superior stability and passivating power, one needs to gain control over the homogeneity, thickness, and phase of the low‐dimensionality layer.