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 (PbI₂) 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.