Cubic Perovskite Structure of Black Formamidinium Lead Iodide, α-[HC(NH2)2]PbI3, at 298 K
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PROVIDER: S-EPMC4603719 | biostudies-literature | 2015 Aug
REPOSITORIES: biostudies-literature
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Project description:Hybrid organic-inorganic perovskites have been one of the most active areas of research into photovoltaic materials. Despite the extremely fast progress in this field, the electronic properties of formamidinium lead iodide perovskite (FAPbI3) that are key to its photovoltaic performance are relatively poorly understood when compared to those of methylammonium lead iodide (MAPbI3). In this study, first-principles total energy calculations based on density functional theory were used to investigate the favored orientation of FA. Different theoretical methods, with or without incorporation of spin-orbit coupling (SOC) effects, were used to study the structure, electronic properties, and charge-carrier effective mass. Also the SOC-induced Rashba k-dependent band splitting, density of states and optical properties are presented and discussed. These results are useful for understanding organic-inorganic lead trihalide perovskites and can inform the search for new materials and design rules.
| S-EPMC9056641 | biostudies-literature
Project description:The fundamental opto-electronic properties of organic-inorganic hybrid perovskites are strongly affected by their structural parameters. These parameters are particularly critical in formamidinium lead iodide (FAPbI3), in which its large structural disorder leads to a non-perovskite yellow phase that hinders its photovoltaic performance. A clear understanding of how the structural parameters affect the opto-electronic properties is currently lacking. We have studied the opto-electronic properties of FAPbI3 using microwave conductivity measurements. We find that the mobility of FAPbI3 increases at low temperature following a phonon scattering behavior. Unlike methylammonium lead iodide (MAPbI3), there are no abrupt changes after the low-temperature β/γ phase transition and the lifetime is remarkably long. This absence of abrupt changes can be understood in terms of the reduced rotational freedom and smaller dipole moment of the formamidinium, as compared to methylammonium.
| S-EPMC5661241 | biostudies-literature
Project description:A challenge of hybrid perovskite solar cells is device instability, which calls for an understanding of the perovskite structural stability and phase transitions. Using neutron diffraction and first-principles calculations on formamidinium lead iodide (FAPbI3), we show that the entropy contribution to the Gibbs free energy caused by isotropic rotations of the FA+ cation plays a crucial role in the cubic-to-hexagonal structural phase transition. Furthermore, we observe that the cubic-to-hexagonal phase transition exhibits a large thermal hysteresis. Our first-principles calculations confirm the existence of a potential barrier between the cubic and hexagonal structures, which provides an explanation for the observed thermal hysteresis. By exploiting the potential barrier, we demonstrate kinetic trapping of the cubic phase, desirable for solar cells, even at 8.2 K by thermal quenching.
| S-EPMC5088641 | biostudies-literature
Project description:We present the formation of a composite film made out of formamidinium lead iodide (FAPI) and molybdenum disulphide quantum dots (MoS2 QDs) and propose a corresponding photovoltaic device architecture based on a 'type-I' alignment of the two materials' electronic energy levels. The introduction of the MoS2 QDs has not compromised the overall crystallinity of the FAPI film and the composite absorber has shown improved stability. We report on the benefits of this composite film and energy band arrangement as the photogenerated carriers in MoS2 QDs, both positive and negative, are injected into the FAPI host matrix, resulting in an increased current density of 24.19 mA cm-2 compared to a current density of 19.83 mA cm-2 for the control device with FAPI only. The corresponding photoconversion efficiency increases from 12.6 to 15.0%. We also show that inclusion of MoS2 QDs in FAPI films resulted in a notable improvement in the fill factor and open-circuit voltage of the solar cells. Most importantly, MoS2 QDs enhanced the film stability by reducing defect formation and acting as passivating agents that minimize recombination losses and improve charge carrier transport. Our results suggest that a composite film in a type-I device architecture can introduce benefits for both future developments in perovskite solar cells and effectively tackling the longstanding challenges of carrier transport in QDs solar cells.
| S-EPMC11405757 | biostudies-literature
Project description:Photodetectors based on three dimensional organic-inorganic lead halide perovskites have recently received significant attention. As a new type of light-harvesting materials, formamidinium lead iodide (FAPbI3) is known to possess excellent optoelectronic properties even exceeding those of methylammonium lead iodide (MAPbI3). To date, only a few photoconductor-type photodetectors based on FAPbI3 single crystals and polycrystalline thin films in a lateral structure have been reported. Here, we demonstrate low-voltage, high-overall-performance photodiode-type photodetectors in a sandwiched geometry based on polycrystalline α-FAPbI3 thin films synthesized by a one-step solution processing method and post-annealing treatment. The photodetectors exhibit a broadband response from the near-ultraviolet to the near-infrared (330-800 nm), achieving a high on/off current ratio of 8.6 × 104 and fast response times of 7.2/19.5 μs. The devices yield a photoresponsivity of 0.95 AW-1 and a high specific detectivity of 2.8 × 1012 Jones with an external quantum efficiency (EQE) approaching 182% at -1.0 V under 650 nm illumination. The photodiode-type photodetectors based on polycrystalline α-FAPbI3 thin films with superior performance consequently show great promise for future optoelectronic device applications.
| S-EPMC6057967 | biostudies-literature
Project description:Thermal annealing on hybrid perovskites is essential to prepare high-quality solar cells with extraordinary efficiency, whose benefits include transformation of inactive phases such as δ-FAPbI3 to active α-FAPbI3. The detailed mechanism for such critical phase transition, however, has not yet been adequately studied. Here, we present multiscale microscopic observation to unravel the anisotropic δ-to-α transition in epitaxial FAPbI3 thin films. We adopt polarized light microscopy that offers enhanced contrast to distinguish isotropic α-FAPbI3 from the anisotropic δ-FAPbI3. Facilitated by in situ heating, it allows us to identify heterogeneous nucleation of α-FAPbI3 and the subsequent diffusional phase transition preferentially occurring along ⟨0001⟩, which is underpinned by the smaller activation energy along the face-sharing direction of PbI6 octahedra. We further reveal the morphology and orientation relationship at the δ-to-α transition front using four-dimensional scanning transmission electron microscopy (4D-STEM), evincing the surface energy dominated orientation rather than the interfacial energy. The presence of high-density planar defects is also discovered at the transition front, which can be considered as an intermediate state facilitating δ-to-α structure transformation. Besides filling the knowledge gap on the phase transition behavior in FAPbI3, our work also demonstrates a multiscale microscopy approach to interrogate the phase transition mechanism in hybrid perovskites.
| S-EPMC11912570 | biostudies-literature
Project description:Formamidinium (FA) lead halide (α-FAPbI3) perovskites are promising materials for photovoltaic applications because of their excellent light harvesting capability (absorption edge 840 nm) and long carrier diffusion length. However, it is extremely difficult to prepare a pure α-FAPbI3 phase because of its easy transformation into a nondesirable δ-FAPbI3 phase. In the present study, a "perovskite" template (MAPbI3-FAI-PbI2-DMSO) structure is used to avoid and suppress the formation of δ-FAPbI3 phases. The perovskite structure is formed via postdeposition involving the treatment of colloidal MAI-PbI2-DMSO film with FAI before annealing. In situ X-ray diffraction in vacuum shows no detectable δ-FAPbI3 phase during the whole synthesis process when the sample is annealed from 100 to 180 °C. This method is found to reduce defects at grain boundaries and enhance the film quality as determined by means of photoluminescence mapping and Kelvin probe force microscopy. The perovskite solar cells (PSCs) fabricated by this method demonstrate a much-enhanced short-circuit current density ( J sc) of 24.99 mA cm-2 and a power conversion efficiency (PCE) of 21.24%, which is the highest efficiency reported for pure FAPbI3, with great stability under 800 h of thermal ageing and 500 h of light soaking in nitrogen.
| S-EPMC6839747 | biostudies-literature
Project description:Formamidinium-lead-iodide (FAPbI3)-based perovskites with bandgap below 1.55 eV are of interest for photovoltaics in view of their close-to-ideal bandgap. Record-performance FAPbI3-based solar cells have relied on fabrication via the sequential-deposition method; however, these devices exhibit unstable output under illumination due to the difficulty of incorporating cesium cations (stabilizer) in sequentially deposited films. Here we devise a perovskite seeding method that efficiently incorporates cesium and beneficially modulates perovskite crystallization. First, perovskite seed crystals are embedded in the PbI2 film. The perovskite seeds serve as cesium sources and act as nuclei to facilitate crystallization during the formation of perovskite. Perovskite films with perovskite seeding growth exhibit a lowered trap density, and the resulting planar solar cells achieve stabilized efficiency of 21.5% with a high open-circuit voltage of 1.13 V and a fill factor that exceeds 80%. The Cs-containing FAPbI3-based devices show a striking improvement in operational stability and retain 60% of their initial efficiency after 140 h operation under one sun illumination.
| S-EPMC5913260 | biostudies-literature
Project description:Formamidinium lead iodide (FAPbI3) is a newly developed hybrid perovskite that potentially can be used in high-efficiency solution-processed solar cells. Here, the temperature-dependent dynamic optical properties of three types of FAPbI3 perovskite films (fabricated using three different precursor systems) are comparatively studied. The time-resolved photoluminescence (PL) spectra reveal that FAPbI3 films made from the new precursor (a mixture of formamidinium iodide and hydrogen lead triiodide) exhibit the longest lifetime of 439 ns at room temperature, suggesting a lower number of defects and lower non-radiative recombination losses compared with FAPbI3 obtained from the other two precursors. From the temperature-dependent PL spectra, a phase transition in the films is clearly observed. Meanwhile, exciton-binding energies of 8.1 and 18 meV for the high- and low-temperature phases are extracted, respectively. Importantly, the PL spectra for all of the samples show a single peak at room temperature, whereas at liquid-helium temperature the emission features two peaks: one in higher energy displaying a fast decay (0.5 ns) and a second red-shifted peak with a decay of up to several microseconds. These two emissions, separated by ~18 meV, are attributed to free excitons and bound excitons with singlet and triplet characters, respectively.
| S-EPMC6059954 | biostudies-literature
Project description:Two-dimensional hybrid organic-inorganic lead halides perovskite-type compounds have attracted immense scientific interest due to their remarkable optoelectronic properties and tailorable crystal structures. In this work, we present a new layered hybrid lead halide, namely [CH(NH2)2][C(NH2)3]PbI4, wherein puckered lead-iodide layers are separated by two small and stable organic cations: formamidinium, CH(NH2)2+, and guanidinium, C(NH2)3+. This perovskite is thermally stable up to 255 °C, exhibits room-temperature photoluminescence in the red region with a quantum yield of 3.5%, and is photoconductive. This study highlights a vast structural diversity that exists in the compositional space typically used in perovskite photovoltaics.
| S-EPMC5867663 | biostudies-literature