The halide perovskite Ruddlesden−Popper (RP) phases are a homologous layered subclass of solution-processable semiconductors that have aroused great attention, especially for developing long-term solar photovoltaics. They are defined as (A′) 2 (A) n−1 Pb n X 3n+1 (A′ = spacer cation, A = cage cation, and X = halide anion). The orientation control of low-temperature selfassembled thin films is a fundamental issue associated with the ability to control the charge carrier transport perpendicular to the substrate. Here we report new chemical derivatives designed from a molecular perspective using a novel spacer cation 3-phenyl-2-propenammonium (PPA) with conjugated backbone as a lowtemperature strategy to assemble more efficient solar cells. First, we solved and refined the crystal structures of single crystals with the general formula (PPA) 2 (FA 0.5 MA 0.5 ) n−1 Pb n I 3n+1 (n = 2 and 3, space group C2) using X-ray diffraction and then used the mixed halide (PPA) 2 (Cs 0.05 (FA 0.88 MA 0.12 ) 0.95 ) n−1 Pb n (I 0.88 Br 0.12 ) 3n+1 analogues to achieve more efficient devices. While forming the RP phases, multiple hydrogen bonds between PPA and inorganic octahedra reinforce the layered structure. For films we observe that as the targeted layer thickness index increases from n = 2 to n = 4, a less horizontal preferred orientation of the inorganic layers is progressively realized along with an increased presence of high-n or 3D phases, with an improved flow of free charge carriers and vertical to substrate conductivity. Accordingly, we achieve an efficiency of 14.76% for planar p−i−n solar cells using PPA-RP perovskites, which retain 93.8 ± 0.25% efficiency with encapsulation after 600 h at 85 °C and 85% humidity (ISOS-D-3).
It is unmistakably paradoxical that the weakest point of the photoactive organic-inorganic hybrid perovskite is its instability against light. Why and how perovskites break down under light irradiation and what happens at the atomistic level of these materials during the degradation process still remains unanswered. In this paper, we revealed the fundamental origin and mechanism for irreversible degradation of hybrid perovskite materials from our new experimental results and ab initio molecular dynamics (AIMD) simulations. We found that the charges generated by light irradiation and trapped along the grain boundaries of the perovskite crystal result in oxygen-induced irreversible degradation in air even in the absence of moisture. The present result, together with our previous experimental finding on the same critical role of trapped charges in the perovskite degradation under moisture, suggests that the trapped charges are the main culprit in both the oxygen-and moisture-induced degradation of perovskite materials. More detailed roles of oxygen and water molecules were investigated by tracking the atomic motions of the oxygen-or water-covered methylammonium lead triiodide (MAPbI3 for CH3NH3PbI3) perovskite crystal surface with trapped charges via AIMD simulation. In the first few picoseconds of our simulation, trapped charges start disrupting the crystal structure, leading to a close-range interaction between oxygen or water molecules and the compositional ions of MAPbI3. We found that there are different degradation pathways depending both on the polarity of the trapped charge and on the kind of gas molecule. Especially, the deprotonation of organic cations was theoretically predicted for the first time in the presence of trapped anionic charges and water molecules. Additionally, we confirmed that a more structurally stable, multi-component perovskite material (with the composition of MA0.6FA0.4PbI2.9Br0.1) exhibited a much longer lifespan than MAPbI3 under light irradiation even in 100% oxygen ambience or humid air.
Perovskite solar cells (PSCs) have shown remarkably improved power-conversion efficiency of around 25%. However, their working principle remains arguable and the stability issue has not been solved yet. In this report, we revealed that the working mechanism of PSCs is explained by a dominant p-n junction occurring at the different interface depending on electron transport layer, and charges are accumulated at the corresponding dominant junction initiating device degradation. Locations of a dominant p-n junction, the electric field, and carrier-density distribution with respect to electron-transport layers in the PCS devices were investigated by using the electron-beam-induced current measurement and Kelvin probe force microscopy. The amount of accumulated charges in the devices was analyzed using the chargeextraction method and the degradation process of devices was confirmed by SEM measurements. From these observations, we identified that the dominant p-n junction appears at the interface where the degree of band bending is higher compared to the other interface, and charges are accumulated at the corresponding junction where the device degradation is initiated, which suggests that there exists a strong correlation between PSC working principle and device degradation. We highlight that an ideal p-i-n PSC that can minimize the degree of band bending should be designed for ensuring long-term stability, via using proper selective contacts
Layered Ruddlesden–Popper perovskite (RPP) photovoltaics have gained substantial attention owing to their excellent air stability. However, their photovoltaic performance is still limited by the unclear real-time charge-carrier mechanism of operating...
Proper control of the morphology and preferred orientation of the SnS absorber is crucial for increasing the open-circuit voltage of thin-film solar cells.
Chiral organic ligand-incorporated low-dimensional metal-halide perovskites have received increasing attention for next-generation photodetectors because of the direct detection capability of circularly polarized light (CPL), which overcomes the requirement for subsidiary optical components in conventional CPL photodetectors. However, most chiral perovskites have been based on low-dimensional structures that confine chiroptical responses to the ultraviolet (UV) or short-wavelength visible region and limit photocurrent due to their wide bandgap and poor charge transport. Here, chiroptical properties of 3D Cs 0.05 FA 0.5 MA 0.45 Pb 0.5 Sn 0.5 I 3 polycrystalline films are achieved by incorporating chiral plasmonic gold nanoparticles (AuNPs) into the mixed Pb-Sn perovskite, without sacrificing its original optoelectronic properties. CPL detectors fabricated using chiral AuNP-embedded perovskite films can operate without external power input; they exhibit remarkable chirality in the near-infrared (NIR) region with a high anisotropy factor of responsivity (g res ) of 0.55, via giant plasmon resonance shift of chiral plasmonic AuNPs. In addition, a CPL detector array fabricated on a plastic substrate demonstrates highly sensitive self-powered NIR detection with superior flexibility and durability.
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