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Currently, photovoltaic/electroluminescent (PV/EL) perovskite bifunctional devices (PBDs) exhibit poor performance due to defects and interfacial misalignment of the energy band. Interfacial energy‐band engineering between the perovskite and hole‐transport layer (HTL) is introduced to reduce energy loss, through adding corrosion‐free 3,3′‐(2,7‐dibromo‐9H‐fluorene‐9,9‐diyl) bis(n,n‐dimethylpropan‐1‐amine) (FN‐Br) into a HTL free of lithium salt. This strategy can turn the n‐type surface of perovskite into p‐type and thus correct the misalignment to form a well‐defined N–I–P heterojunction. The tailored PBD achieves a high PV efficiency of up to 21.54% (certified 20.24%) and 4.3% EL external quantum efficiency. Free of destructive additives, the unencapsulated devices maintain >92% of their initial PV performance for 500 h at maximum power point under standard air mass 1.5G illumination. This strategy can serve as a general guideline to enhance PV and EL performance of perovskite devices while ensuring excellent stability.

A nonuniform vertical phase distribution and thick insulating barrier can decrease the energy transfer between slices in layered perovskite solar cells (PSCs). Herein, an interlayer cross‐linked Dion–Jacobson (DJ)‐type 2D PSC with 1,4‐butanediamine (BDA) as a short‐chain insulating spacer [formula: (BDA)MAn −1PbnI3n + 1] is reported and demonstrates the vertical phase becoming uniform with enhanced exciton coupling, leading to reduced nonradiative recombination. For n = 1 pure phase perovskite, an exciton binding energy of the DJ phase (BDA)PbI4 is ≈142 meV, much smaller than ≈435 meV of Ruddlesden–Popper (RP) phase (BA)2PbI4 (n = 1) perovskite, indicative of exciton‐coupling‐induced efficient energy transfer. Therefore, the high energy emission peaks for the (BDA)MA3Pb4I13 film are not observed even in liquid nitrogen temperature (78 K), which can be distinguished from that of the (BA)2MA3Pb4I13 film. Energy transfer between 2D slices of (BDA)MA3Pb4I13 is 100 times faster than that of (BA)2MA3Pb4I13. The uniform vertical distribution and exciton coupling mitigate nonradiative energy loss and significantly improve Voc in inverted structures (PEDOT:PSS/(BDA)MA3Pb4I13/PCBM/bathocuproine/Ag) to ≈1.15 V and the control n‐butylammonium‐based device demonstrates only a Voc = ≈1 V. It is believed that the results would provide a deep understanding of exciton coupling in hybrid multicomponent quantum wells.

The efficiency of perovskite solar cells (PSCs) has been boosted from power conversion efficiency (PCE) of 3.8% [1] to 25.2% [2] in ten years, providing the further possibility for commercialization. The general chemical formula for 3D perovskite is known as ABX 3 , where A typically is methylammonium (MA +), formamidinium ions (FA 2+), B is lead or tin, and X is usually halide element (I, Cl, and Br). Conventionally, formamidinium and methylammonium ions mixed (FAMA-mixed), [3] cesium, formamidinium and methylammonium ions mixed (CsFAMA-mixed), [4] and cesium and formamidinium ions mixed (CsFA-mixed) [5] perovskites are mostly investigated due to their strong absorption [6] in visible spectrum, suitable bandgap, excellent carrier transport properties, [7,8] and the low-temperature fabrication technique. However, the lifetime of perovskite solar cells is still far shorter than that of the traditional silicon solar cells. Recently, a 2D type perovskite emerges as a promising alternative to enhance the photovoltaic lifespan. Different from conventional 3D perovskite structure, the 2D perovskite typically employs large molecular ligands that do not fill into the perovskite structure but split the 3D perovskite framework into slices, yielding layered perovskite structure. The 2D perovskite generally holds the chemical formula (L) 2 A n-1 B n X 3n+1 or L′A n-1 B n X 3n+1 , where L/L′ is a mono/divalent amino-group ended long-chain ligand. Depending on the number of amino-group, 2D perovskite can be divided into Ruddlesden-Popper phase (RP) or Dion-Jacobson phase (DJ) phase. In terms of structure difference, there is a bilayer of organic ligands separating the octahedral BX 6 framework apart in RP phase perovskite, whereas there is only one monolayer ligand in the case of DJ phase perovskite. [9] This monolayer will introduce smaller interlayer distance and bring the slice structure more closely, leading to the formation of a superlattice with enhanced exciton interaction. [10] The emergence of 2D perovskite offers a wide possibility to tailor long-chain organic molecules and further the orientation, distribution of 2D phase components, enabling highly efficient and stable perovskite solar cells. However, the mixture of 2D phases will inevitably introduce additional carrier transport loss when carriers travel across different 2D perovskite The crystalline orientation and phase distribution are two important parameters for high-performance 2D perovskite solar cells. Therefore, it is essential to understand how the structure of spacer ligands influences the orientation and phase distribution of resulting 2D perovskite films. In this work, a new member of Dion-Jacobson (DJ) phase 2D perovskites based on trans-1,4-cyclohexanediamine (CHDA) is demonstrated and it is found that the crystalline orientation is self-aligned spontaneously, which is different from the well-known graded distribution in controlled sample with its isomer 1,6-diaminohexane (HDA) as spacer ligand. Grazing incident X-ray scattering suggests that the ex...

Light soaking (LS) has been reported to positively influence the device performance of perovskite solar cells (PSCs), which, however, could be potentially harmful to the loaded devices due to the unstable output. There are very few reports on controls over the LS effect, especially in all‐inorganic PSCs. In this study, a remarkable LS induced performance enhancement of CsPb(I1−xBrx)3 based PSCs is presented. In situ grazing‐incidence wide‐angle X‐ray scattering measurements quantize the temperature increase under illumination and reveal a radiative heating‐induced lattice expansion. The device curing time is shortened with the increased Br/I ratio, evidently correlated with their distinct mobility and activation energy. It is suggested that LS could promote the migration of halide ions, giving rise to notable defect passivation and thus device improvements. Based on these understandings, an effective means is proposed to suppress the LS effect, which is to incorporate slightly over‐stochiometric PbI2 in precursor, and a champion PCE of 18.14% in all‐inorganic PSCs with significantly reduced device curing time is obtained.