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PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a distorted T-shaped geometry to three equivalent Pb2+ atoms.
PbI2 is trigonal omega structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one PbI2 sheet oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.
PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of six PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.
PbI2 is trigonal omega-like structured and crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of three PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.
PbI2 is trigonal omega-like structured and crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of five PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.
PbI2 is trigonal omega-like structured and crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of seven PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.
PbI2 is trigonal omega-like structured and crystallizes in the hexagonal P6_3mc space group. The structure is two-dimensional and consists of two PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a distorted T-shaped geometry to three equivalent Pb2+ atoms.
PbI2 is trigonal omega-like structured and crystallizes in the hexagonal P6_3mc space group. The structure is two-dimensional and consists of four PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a distorted T-shaped geometry to three equivalent Pb2+ atoms.
PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of six PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. There are two inequivalent I1- sites. In the first I1- site, I1- is bonded in a distorted T-shaped geometry to three equivalent Pb2+ atoms. In the second I1- site, I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.
PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of twelve PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.28 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.
PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of nine PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. There are three shorter (3.28 Å) and three longer (3.29 Å) Pb–I bond lengths. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.
PbI2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of nine PbI2 sheets oriented in the (0, 0, 1) direction. Pb2+ is bonded to six equivalent I1- atoms to form edge-sharing PbI6 octahedra. All Pb–I bond lengths are 3.30 Å. I1- is bonded in a 3-coordinate geometry to three equivalent Pb2+ atoms.
Lead iodide (PbI2) has gained much interest due to its direct electronic gap in the visible range and layered crystal structure. It has thereby been considered as a promising material for applications in atomically thin optoelectronic devices. In this work, we present a detailed investigation of the effect of spin–orbit coupling (SOC) that arises from the presence of heavy atoms on the electronic and optical properties of PbI2 using first-principles calculations based on density-functional theory and many-body perturbation theory. We find that SOC not only alters the bandgap but also induces the mixing of orbital characters, resulting in a significant change in the overall band structure and charge carrier effective masses. Moreover, the band orbital mixing caused by SOC results in the dramatic change in optical transition matrix elements and, correspondingly, the absorption spectrum. Our experimentally measured absorption spectra validate the calculation results and demonstrate the importance of SOC in the optical processes of PbI2. Our findings provide insights that are important for the potential use of PbI2 as a material platform for visible optoelectronic devices.
Chiral hybrid metal-halide perovskites show low-symmetry crystal structures, large Rashba splitting, spin-filtering, and strong chiroptical activity. Circular dichroism and circularly polarized photoluminescence have been investigated in chiral perovskites with increasingly distorted chiral structures. Here, we report the fabrication of chiral (R/S)-EBAPbI3 (EBA = α-ethylbenzylamine) single crystals, which possess highly distorted octahedral structures with a high angle variance value of ∼68 degree2. Using control in the fabrication conditions, we transfer chiral single crystals to thin films and achieve different crystal orientation preferences that induce tunable chiroptical properties to their heterostructures with PbI2 nanodomains, which we characterize with in situ X-ray diffraction and grazing-incidence wide-angle X-ray scattering measurements. Using transient chiroptical spectroscopies, we resolve photoexcited charge carrier dynamics and chirality transfer processes in such heterostructures down to cryogenic temperatures. We observe rapid carrier transfer along the in-plane (002) facets in chiral perovskite phases to PbI2 nanostructures within the initial few picoseconds, while carrier transfer along the out-of-plane (002) facets occurs at a slower rate. This fast transfer process leads to high photoluminescence intensities and large degrees of circular polarization in the emission from PbI2 nanodomains at cryogenic temperatures. Our findings report a multidimensional chiral-achiral heterostructure which takes advantage of controllable chirality transfer and offers new routes for future spintronic and chiroptical applications.
One of the key challenges of perovskite photovoltaics (PV) is the long-term stability. Although efforts are made to improve the lifetime of perovskite PV devices, their degradation under reverse-bias conditions is barely addressed. Herein, perovskite solar cells with carbon-based electrodes are presented which demonstrate superior resilience against reverse-bias-induced degradation. Although their breakdown voltage is identified to be at approximately -3.6 V, cells do not degrade until the applied reverse-bias exceeds -9 V. Two main degradation mechanisms are identified: 1) iodine loss due to hole tunneling into perovskite, which takes place even at low reverse-bias but decomposes the perovskite only after long time durations; and 2) rapid heating at large reverse-bias leading to formation of PbI2, which starts at shunts and then follows the path of the least resistance for the cell current, which is primarily influenced by the electrode sheet resistances. Finally, perovskite solar modules with carbon-based electrodes are demonstrated, which are subjected to a "hotspot" test described in the IEC 61215:2016 international standard at an accredited module testing laboratory. Passing this accelerated test for the first time confirms the superior stability of perovskite PV devices with carbon-based electrodes and highlights their large industrialization potential.
Single-source vapor deposition of halide perovskites has, to date, remained challenging due to the dissimilar volatilities of the precursors, limiting the controlled transfer of multiple elements at once. Here, we demonstrate that pulsed laser deposition (PLD) addresses the rate-control challenges of single-source evaporation, enabling perovskite solar cells with power conversion efficiencies above 19% after passivation. Combining dry mechanochemical synthesis and PLD, we fabricated (Cl-passivated) MA1−xFAxPbI3 films from a single-source target. These films grow on hole-selective self-assembled monolayers, initially forming a thin PbI2-rich layer, which fully converts to perovskite. An oleylammonium iodide (OAmI) post-treatment is then applied to passivate the perovskite’s top surface by forming a 2D perovskite film. Incorporating PbCl2 in the target and applying OAmI-based 2D passivation results in a remarkable 19.7% efficiency for p-i-n perovskite solar cells with enhanced device stability. This highlights the appeal of PLD to fully unlock the potential of single-source vapor-deposited perovskites.
Metal halide perovskites are considered the most promising candidates for solar cells of the decade due to their exceptional optical and electronic properties. The power conversion efficiency of metal halide perovskites, when incorporated as the active layer of solar cells, has become comparable to that observed for conventional silicon solar cells. However, the stability, scaleup, green solvent usage, and fabrication in ambient conditions of metal halide perovskites need to be solved for commercial applications. Here, in this work, we report the fabrication of blade-coated methylammonium lead iodide (MAPbI 3 ) perovskite thin films using methylamine and acetonitrile as “green” solvents under ambient conditions. Our perovskite films are initially prepared from low purity PbI2 (99%) and are blade-coated in dry air at relative humidity (RH) levels above 30%. A significant advantage of fabricating our perovskite thin films via blade-coating protocols is that there is a minimal amount of precursors (5 μL) used compared to spin-coating methods (50μL–60μL) for a 4 cm 2 substrate. With the addition of a small amount of an organic halide salt, namely, phenethylammonium chloride, the film crystallinity is improved and non-radiative recombination is suppressed, resulting in power conversion efficiencies over 20%. In addition, the device maintains more than 95% of its initial efficiency after 500 h under continuous light illumination of 1-sun at open circuit conditions, 50 °C and 60% RH. The above method leads a path towards the commercial fabrication of perovskite solar cells.
Three leading thin-film photovoltaic (PV) technologies - cadmium telluride (CdTe), CuIn1-xGaxSe2 (CIGS), and perovskite solar cells (PSCs) - are all polycrystalline, but otherwise appear to have little in common. A comprehensive examination of these technologies, however, reveals a common theme: the formation of two-dimensional (2D) van der Waals materials at three-dimensional (3D) absorber interfaces and grain boundaries. In CdTe, the 2D compound is CdCl2; in CIGS, it is XInSe2 (X= K, Rb, Cs) with X depending on the heavy-alkali post-deposition treatment used; and in lead halide PSCs, PbI2 forms naturally, but many new, more stable, 2D perovskites have also been incorporated. Generally, these 2D interfacial materials are present not by design, but instead have evolved from their 3D counterparts during standard device processing. Here, new data, together with evidence compiled from the literature, are presented to illustrate both the existence of 3D/2D interfaces in CdTe, CIGS, and PSCs, and their correlation with improved passivation and device performance. This suggests that 3D/2D passivation may be a heretofore unappreciated key to successful polycrystalline thin-film PV. Finally, the desired attributes of successful low-dimensional layers are presented with rational design strategies for next generation polycrystalline solar cells.