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...
Passivation by small organic compounds can reduce the trap density and enhance the humidity and illumination stability of perovskite solar cells (PSCs). However, the small molecule passivated on the perovskite film cannot endure harsh heat stress. Herein, we find that the trichloro(octyl)silane (TC-silane) is an excellent candidate to modify the perovskite surface and grain boundary nondestructively through the formation of a heat-resistive silicone layer, leading to a comprehensive improvement of efficiency and stability with low cost as well as facile fabrication. The silane is a type of solvent and can be upscaled by a solution process in the device. TC-silicone can cross-link the grain boundaries through hydrolytic condensation. The cross-linking silicone can resist the moisture and heat stresses to enhance the stability. Also, microphotoluminescence reveals that TC-silane treatment can passivate the perovskite film and enhance the optoelectronic properties through chloride replenishment by releasing a hydrogen chloride molecule in the hydrolytic reaction. By utilizing Kevin probe force microscopy, we further uncover that TC-silane forms a dipole layer to facilitate the charge separation. TC-silane passivated PSCs deliver a champion efficiency of 20.03% and remain at 80% of their initial efficiency for more than 800 h at 70−80% relative humidity in air and for about 80 h under 85 °C thermal stress without encapsulation.
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