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Abstract 2D‐on‐3D (2D/3D) perovskite heterostructures present a promising strategy to realize efficient and stable photovoltaics. However, their applicability in inverted solar cells is limited due to the quantum confinement of the 2D‐layer and solvent incompatibilities that disrupt the underlying 3D layer, hampering electron transport at the 2D/3D interface. Herein, solvent‐dependent formation dynamics and structural evolution of 2D/3D heterostructures are investigated via in situ X‐ray scattering. It is revealed that solvent interaction with the 3D surface determines the formation sequence and spatial distribution of quasi‐2D phases withn= 2–4. Isopropanol (IPA) reconstructs the perovskite into a PbI₂‐rich surface, forming a strata with smallernfirst, followed by a thinner substratum of largern. In contrast, 2,2,2‐Trifluoroethanol (TFE) preserves the 3D surface, promoting the formation of uniformly distributed largerndomains first, and smallernlast. Leveraging these insights, Dion–Jacobson perovskites are used with superior charge transport properties and structural robustness to fabricate 2D/3D heterostructures dominated byn≥ 3 and engineer a favorable energy landscape for electron tunneling. Inverted solar cells based on 3‐Aminomethylpyridine and TFE achieve a champion efficiency of 23.60%, withV_ocand FF of 1.19 V and 84.5%, respectively, and superior stabilities witht₉₄of 960 h under thermal stress. 

Recently, carbazole-based organic cations have garnered interest for their potential application in two-dimensional (2D) layered hybrid perovskite solar cells because of their strong hole extraction and transport as well as humidity resistance. However, the potential incorporation of carbazole-based Ruddlesden–Popper 2D hybrid perovskites in photodetectors has been largely unexplored. In this study, we synthesized ammonium 1-(9H-carbazol-9-yl) ethanaminium iodide (CzEAI) and fabricated (CzEA)2PbI4 2D perovskite thin films via varying solvent conditions to control film morphology. We constructed photodiode-type photodetectors with the active layer of (CzEA)2PbI4 2D perovskites and demonstrated a specific detectivity of 6.95 × 1010 Jones at 485 nm illumination without external bias. These results demonstrate the potential of carbazole-based 2D perovskites in a wide range of optoelectronic applications. 

2D Ruddlesden–Popper perovskites have risen to prominence as stable and efficient photovoltaic materials because of their structural diversity, rich photophysics, and low moisture ingression. However, thin films processed from stoichiometric precursor solutions possess a broad phase distribution of different number of inorganic layers with random crystal orientation, crippling device performance. The effect of methylammonium chloride (MACl) and 3‐amino‐4‐phenolsulfonic acid (APSA) on the fabrication of perpendicularly oriented (PEA)₂MA₄Pb₅I₁₆films with narrow phase distribution using antisolvent and hot‐casting processing techniques is investigated. MACl plays a critical role in suppressing parasiticn ≤ 2 and 3D‐like phases. APSA performs the dual function of trap passivation and further narrowing phase polydispersity through strong coordination with Pb²⁺. Ex situ grazing‐incident wide‐angle X‐Ray scattering (GIWAXS) and ultrafast spectroscopic characterization reveal uniformly mixed‐phase distribution with disordered orientation in antisolvent treated films, while additive‐assisted hot‐casting treatment results in oriented, reverse‐graded phase distribution, i.e., small‐non the film surface and large‐nat the bottom. Arising thin films enable efficient p–i–n solar cells with an efficiency of 14.34%, and aV_ocof 1.20 V, retaining 96% initial efficiency after 1440 h under ambient conditions (RH = 50–60%) without encapsulation.