Directing efficient hole transport Surface defects in three-dimensional perovskites can decrease performance but can be healed with coatings based on two-dimensional (2D) perovskite such as Ruddlesden-Popper phases. However, the bulky organic groups of these 2D phases can lead to low and anisotropic charge transport. F. Zhang et al . show that a metastable polymorph of a Dion-Jacobson 2D structure based on asymmetric organic molecules reduced the energy barrier for hole transport and their transport through the layer. When used as a top layer for a triple-cation mixed-halide perovskite, a solar cell retained 90% of its initial power conversion efficiency of 24.7% after 1000 hours of operation at approximately 40°C in nitrogen. —PDS

The band edges of metal-halide perovskites with a general chemical structure of ABX3 (A, usually a monovalent organic cation; B, a divalent cation; and X, a halide anion) are constructed mainly of the orbitals from B and X sites. Hence, the structural and compositional varieties of the inorganic B–X framework are primarily responsible for regulating their electronic properties, whereas A-site cations are thought to only help stabilize the lattice and not to directly contribute to near-edge states. We report a π-conjugation–induced extension of electronic states of A-site cations that affects perovskite frontier orbitals. The π-conjugated pyrene-containing A-site cations electronically contribute to the surface band edges and influence the carrier dynamics, with a properly tailored intercalation distance between layers of the inorganic framework. The ethylammonium pyrene increased hole mobilities, improved power conversion efficiencies relative to that of a reference perovskite, and enhanced device stability.

The long‐term operational stability of perovskite light‐emitting diodes (PeLEDs), especially red PeLEDs with only several hours typically, has always faced great challenges. Stable β‐CsPbI3 nanocrystals (NCs) are demonstrated for highly efficient and stable red‐emitting PeLEDs through incorporation of poly(maleic anhydride‐alt‐1‐octadecene) (PMA) in synthesizing the NCs. The PMA can chemically interact with PbI2 in the precursors via the coupling effect between O groups in PMA and Pb2+ to favor crystallization of stable β‐CsPbI3 NCs. Meanwhile, the cross‐linked PMA significantly reduces the PbCs anti‐site defect on the surface of the β‐CsPbI3 NCs. Benefiting from the improved crystal phase quality, the photoluminescence quantum yield for β‐CsPbI3 NCs films remarkably increases from 34% to 89%. The corresponding red‐emitting PeLEDs achieves a high external quantum efficiency of 17.8% and superior operational stability with the lifetime, the time to half the initial electroluminescence intensity (T50) reaching 317 h at a constant current density of 30 mA cm−2.

Surface treatment using large alkyl/aryl ammonium cations has demonstrated reduced open-circuit voltage (V OC ) deficits in perovskite solar cells (PSCs), but the origin of the improvements has been vaguely attributed to defect passivation. Here, we combine microscopic probing of the local electrical properties, thermal admittance spectroscopic analysis, and firstprinciples calculations to elucidate the critical role of arylammonium interface layers in suppressing ion migration in wide-bandgap (WBG) PSCs. Our results reveal that arylammonium surface treatment using phenethylammonium iodide increases the activation energy barrier for ion migration on the surface, which suppresses the accumulation of charge defects at surface and grain boundaries, leading to a reduced dark saturation current density in WBG PSCs. With device optimization, our champion 1.73 eV PSC delivers a power conversion efficiency of 19.07% with a V OC of 1.25 V, achieving a V OC deficit of 0.48 V.

photovoltaic (PV) technologies. While most of the research efforts have focused on lead (Pb)-based MHP single junction PV cells, MHP-based tandem solar cells fabricated by combining MHP layers with silicon, Cu(In, Ga)Se 2 (CIGS), or another low-bandgap MHP are gaining increasing attention because of their potential to overcome the detailed balance limit of single junction PV cells and thus leading to a further reduction in the cost of PV technologies. [8][9][10][11][12] Among these technologies, MHP-MHP tandem cells can be fabricated employing all solution-based processes to retain the low-fabrication cost merit yet still retain high PCEs and flexible. [13,14] Narrow-bandgap (NBG) tin (Sn)-Pb perovskites can reach a lowest bandgap of 1.21 eV with a Sn/Pb ratio of ≈1, which paired with a wide-bandgap (WBG) MHP with a bandgap of 1.80 eV can reach a maximum efficiency of over 30%. [14,13] As a crucial part of MHP-MHP tandem cells, the Sn-Pb NBG perovskite single-junction solar cells still have low PCEs compared to their bandgap entitlement in order realize the full potential of tandem structures. [7,14,15] The best certified PCE for a Sn-Pb NBG single junction solar cells to date is 20.7%, [16] which is much lower than that of silicon or CIGS single junction cells. There are still several obstacles for further improvement of Sn-Pb perovskite, such as low absorption coefficient [17] prone to be oxidized, [18] poor thermal [19] stability, high self p-doping, [17,20] and relatively short carrier diffusion length. [17] Due to the relatively smaller absorption coefficient compared to Pb perovskites, Sn-Pb NBG absorbers must be at least 1 µm thick to ensure efficient light absorption, and a commensurate increase of the minority-carrier diffusion lengths into the several µm range are needed to ensure efficient charge collection. The most outstanding challenge limiting long carrier diffusion lengths in Sn-Pb NBG perovskites is reportedly the presence of a high density of residual p-type carriers. [17,20] The p-type self-doping is known to be induced by Sn vacancies which generally pair with Sn 4+ to maintain charge neutrality. [21][22][23] Sn 2+ is thermodynamically instable for the low oxidation potential of E O = 0.15 V for Sn 2+ /Sn 4+ . [23][24][25] Therefore, Sn vacancies are prone to form upon oxidation of Sn 2+ to Sn 4+ which can occur during any step of the device construction from raw materials up to encapsulated Sn-Pb perovskite-based Narrow-bandgap (NBG) tin (Sn)-lead (Pb) perovskites generally have a high density of unintentional p-type self-doping, which reduces the charge-carrier lifetimes, diffusion lengths, and device efficiencies. Here, a p-n homojunction across the Sn-Pb perovskite is demonstrated, which results from a gradient doping by barium ions (Ba 2+ ). It is reported that 0.1 mol% Ba 2+ can effectively compensate the p-doping of Sn-Pb perovskites or even turns it to n-type without changing its bandgap. Ba 2+ cations are found to stay at the interstitial sites and work as shallow electron donor. In a...