Binary Perovskite Research Articles

Metal-bonded perovskite lead hydride with phonon-mediated superconductivity exceeding 46 K under ambient pressure

In the search for high-temperature superconductivity in hydrides, a plethora of multi-hydrogen superconductors have been theoretically predicted, and some have been synthesized experimentally under ultrahigh pressures of several hundred GPa. However, the impracticality of these high-pressure methods has been a persistent issue. In response, we propose a new approach to achieve high-temperature superconductivity under ambient pressure by implanting hydrogen into lead to create a stable few-hydrogen binary perovskite, Pb4H. This approach diverges from the popular design methodology of multi-hydrogen covalent high critical temperature (Tc ) superconductors under ultrahigh pressure. By solving the anisotropic Migdal–Eliashberg equations, we demonstrate that perovskite Pb4H presents a phonon-mediated superconductivity exceeding 46 K with inclusion of spin–orbit coupling, which is six times higher than that of bulk Pb (7.22 K) and comparable to that of MgB2, the highest Tc achieved experimentally at ambient pressure under the Bardeen, Cooper, and Schrieffer framework. The high Tc can be attributed to the strong electron–phonon coupling strength of 2.45, which arises from hydrogen implantation in lead that induces several high-frequency optical phonon modes with a relatively large phonon linewidth resulting from H atom vibration. The metallic-bonding in perovskite Pb4H not only improves the structural stability but also guarantees better ductility than the widely investigated multi-hydrogen, iron-based and cuprate superconductors. These results suggest that there is potential for the exploration of new high-temperature superconductors under ambient pressure and may reignite interest in their experimental synthesis in the near future.

Improved Efficiency and Stability of Perovskite Solar Cells by Binary Perovskite–Organic Composite Thin Film

Regulating perovskite film crystallization and avoiding bulk defects during the deposition process are essential for achieving perovskite solar cells (PSCs) with excellent power conversion efficiency (PCE) and stability. Herein, the synergistic effects between n‐type, narrow‐bandgap conjugated organic molecules (2,2′‐((2Z,2′Z)‐((5,5′‐(4,4,9,9‐tetrakis(4‐hexylphenyl)‐4,9‐dihydros‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(4‐((2‐ethylhexyl)oxy)thiophene‐5,2‐diyl))bis(methanylylidene))bis(3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile [IEICO]) and perovskites on film surface morphology and stability, and the regulation mechanism on bulk defects in MAPb(I0.97Br0.03)3:IEICO films are explored. The results of theoretical and experimental studies indicate that a large number of electrons on the CO and C≡N surface functional groups of IEICO can function as Lewis bases and exhibit strong interactions with uncoordinated Pb2+ ions, substantially reducing bulk defects. Moreover, the resulting MAPb(I0.97Br0.03)3:IEICO film exhibits an optical response in the near‐infrared region and an increased crystallite size. Consequently, the MAPb(I0.97Br0.03)3:IEICO PSCs with a p–i–n device structure demonstrate a PCE exceeding 20%. In addition, the MAPb(I0.97Br0.03)3:IEICO PSCs possess superior stability and negligible photocurrent hysteresis. These results suggest that the incorporation of near‐infrared organic molecules into perovskites provides a simple method to achieve high‐performance PSCs and realize the utilization of near‐infrared wavelengths.

Ternary-Metal Sn-Pb-Zn Perovskite to Reconstruct Top Surface for Efficient and Stable Less-Pb Perovskite Solar Cells.

Though Sn-Pb alloyed perovskite solar cells (PSCs) achieved great progress, there is a dilemma to further increase Sn for less-Pb requirement. High Sn ratio (>70%) perovskite exhibits nonstoichiometric Sn:Pb:I at film surface to aggravate Sn2+ oxidation and interface energy mismatch. Here, ternary metal alloyed (FASnI3 )0.7 (MAPb1- x Znx I3 )0.3 (x = 0-3%) is constructed for Pb% < 30% perovskite. Zn with smaller ionic size and stronger ionic interaction than Sn/Pb assists forming high-quality perovskite film with ZnI6 4- enriched at surface to balance Sn:Pb:I ratio. Differing from uniform bulk doping, surface-rich Zn with lower lying orbits pushes down the energy band of perovskite and adjusts the interface energy for efficient charge transfer. The alloyed PSC realizes efficiency of 19.4% at AM1.5 (one of the highest values reported for Pb% < 30% PSCs). Moreover, stronger bonding of Zn─I and Sn─I contributes to better durability of ternary perovskite than binary perovskite. This work highlights a novel alloy method for efficient and stable less-Pb PSCs.

Component Distribution Regulation in Sn-Pb Perovskite Solar Cells through Selective Molecular Interaction.

Tin-lead (Sn-Pb) perovskite solar cells (PSCs) with near-ideal bandgap still lag behind the pure lead PSCs. Disordered heterojunctions caused by inhomogeneous Sn/Pb ratio in the binary perovskite film induce large recombination loss. Here, an Sn-Pb perovskite film is reported with homogeneous component and energy distribution by introducing hydrazine sulfate (HS) in Sn perovskite precursor. HS can form hydrogen bond network and coordinate with FASnI3 thus no longer bond with Pb2+ , which reduces the crystallization rate of tin perovskite to the level of lead analog. The strong bonding between SO4 2- and Sn2+ can also suppress its oxidation. As a result, the Sn-Pb PSCs with HS exhibit a significantly improved VOC of 0.91 V along with a high efficiency of 23.17%. Meanwhile, the hydrogen bond interaction network, strong bonding between Sn2+ and sulfate ion also improve the thermal, storage, and air stability of resulting devices.

Sub-millimetre light detection and ranging using perovskites

Light detection and ranging (LiDAR) technology is an active remote-sensing system used in autonomous vehicles, machine vision and augmented reality. Improvements in the speed and signal-to-noise ratio of photodetectors are needed to meet these demanding ranging applications. Silicon electronics have been the principal option for LiDAR photodetectors in the range of 850–950 nm. However, its indirect bandgap leads to a low absorption coefficient in the near-infrared region, as well as a consequent trade-off between speed and efficiency. Here we report solution-processed lead–tin binary perovskite photodetectors that have an external quantum efficiency of 85% at 850 nm, dark current below 10–8 A cm–2 and response time faster than 100 ps. The devices are fabricated using self-limiting and self-reduced tin precursors that enable perovskite crystallization at the desired stoichiometry and prevent the formation of interfacial defects with the hole transport layer. The approach removes oxygen from the solution, converts Sn4+ to Sn2+ through comproportionation, and leaves neither metallic tin nor SnOx residues. To illustrate the potential of these solution-processed perovskite photodetectors in LiDAR, we show that they can resolve sub-millimetre distances with a typical 50 µm standard deviation.

Reducing the Energy Loss to Achieve High Open‐circuit Voltage and Efficiency by Coordinating Energy‐Level Matching in Sn–Pb Binary Perovskite Solar Cells

Tin–lead (Sn–Pb) binary low‐bandgap perovskites are more environmentally friendly than conventional Pb‐based perovskites and promise to deliver high photovoltaic performance by constructing tandem solar cells. However, the energy‐level mismatch between functional layers and tremendous trap states in perovskite films make it challenging to reduce the high open‐circuit voltage (Voc) loss in Sn–Pb binary perovskite solar cells (PSCs). Herein, energy loss reduction at the hole collection interface in Sn–Pb binary PSCs is demonstrated using nickel oxide (NiOx) as the hole transport material (HTM) with optimal poly[(9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctyfluorene)] (PFN) modification, which enables a significantly enhanced Voc compared to the traditional poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)‐based devices. The NiOx/PFN bilayer has a downward‐shifted valence band compared to PEDOT:PSS, providing well‐matched energy‐level alignment with the perovskite material, resulting in more fluent charge transfer and reduced Voc losses. The optimized device has a high Voc of 0.88 V and an efficiency of 19.80%, surpassing the previous results reported for NiOx‐based Sn–Pb PSCs. Moreover, the robust NiOx/PFN substrate and the high‐quality perovskite film grown on it make the device less vulnerable to ambient exposure. This work highlights the significance of ideal hole conductors and interface engineering in efficient and stable Sn–Pb low‐bandgap PSCs.

Preferred Film Orientation to Achieve Stable and Efficient Sn-Pb Binary Perovskite Solar Cells.

The preferred orientation of crystalline films in hybrid perovskite materials is known to influence the performance of perovskite solar cells (PSCs). Although the preferred growth along the (112) directions has been reported to promote charge transport within the Pb-based polycrystalline perovskite films, the preferred orientation growth of this facet is still difficult to be achieved due to the higher formation energy compared with the (110) plane. Herein, Sn-Pb binary perovskite films with a well-controlled orientation along the (224) plane were achieved by introducing a simple ultrasonic treatment (UST) into the additive engineering fabricated method. UST is used to process the perovskite precursor solutions of tartaric acid (TA) modified Sn-Pb binary polycrystalline perovskite films to regulate the interactions between PbI2/SnI2 and TA in the intermediate phases. Meanwhile, TA-modulated MA0.9Cs0.1Pb0.75Sn0.25I3-based perovskite films with a preferred orientation of (224) crystal plane were obtained by precisely controlling the UST time to 15 min. The highest power conversion efficiency (PCE) of 15.59% with less hysteresis and improved stability was achieved, while realizing 8.64 and 25.32% enhancements of PCE compared with that of TA-based and control counterparts with (110) preferred orientation, respectively. Our work provides a promising route to obtain preferred orientation growth of polycrystalline perovskite films. In particular, we have shown that this approach improves the performance of Sn-Pb binary PSCs, while such methodology is quite flexible and could also be applied to other low-/non-toxic PSCs.

Roles of Sn content in physical features and charge transportation mechanism of Pb-Sn binary perovskite solar cells

Tin (Sn)-based perovskites are a low-toxic and eco-friendly alternative because of their faster tendency to form inert oxides which have much lower bio-availability than lead-based perovskites. Therefore, at present paper, different properties of Pb-Sn binary perovskite solar cells (CH3NH3SnxPb1 – xI3 [0 ≤ x ≤ 1]) were investigated under ambient conditions without the use of encapsulation techniques. For the first time, cauliflower-like morphologies of Sn/Pb mixed perovskites were synthesized and their structural quantitatively analyzed using modified (Monshi) Scherrer (M-Sch) and Williamson-Hall (W-H) methods. The electrical characterization of the cells revealed that incorporating Sn ions into the Pb-based perovskite not only dramatically reduces the carrier density but also from the molar ratio of x = 0.25 to higher values, it converts the electrical conduction behavior from p- to n-type. This effect could be considered as one of the effective factors in reducing the efficiency (η) of solar cells from 16.83% for CH3NH3PbI3 to 0.86% for CH3NH3SnI3. Therefore, choosing an appropriate strategy against this electrical conductivity behavior could help us to achieve a new approach to reducing the toxicity of perovskite solar cells with the least reduction in their efficiency.

Catalytic Activity of Lanthanide-Doped Sr2PdO3 for the Hydrogen Evolution Reaction in Fuel Cells

The electrocatalytic activity of Ln0.3Sr1.7PdO3 (Ln = La, Nd, or Gd) perovskites prepared by the citrate combustion method for the hydrogen evolution reaction (HER) was examined by electrochemical techniques. The X-ray diffraction data indicate the formation of Sr2PdO3 and SrPd3O4 as primary and secondary phases, respectively, with the LnPd alloy only appearing in the Gd3+-doped sample. Transmission electron microscopy images clearly show the orthorhombic geometry of Sr2PdO3 in all samples, and the particle size decreased and the Brunauer–Emmett–Teller surface area increased as the dopant ionic size decreased. Potentiodynamic cathodic polarization measurements show that lanthanide doping at the Sr2+ site increased the catalytic activity toward the HER compared to that of the undoped binary perovskite, Sr2PdO3, except for the La3+-doped sample. The order of catalytic activity is Gd0.3Sr1.7PdO3 > Nd0.3Sr1.7PdO3 ≈ Sr2PdO3 > La0.3Sr1.7PdO3, which is consistent with the impedance data and activation energy calculations. This order is probably related to the amount of the secondary phase, SrPd3O4, contained in each sample, which not only contributes to the activity but also prevents the catalyst from being deactivated. Of all the prepared ternary perovskites, Ln0.3Sr1.7PdO3 shows considerable operational stability, making it a promising HER catalyst.

Effect of atomic configuration on band gap behaviour in CH3NH3SnxPb1−xI3 perovskites

The atomic structure and electronic properties of Sn/Pb mixed organometal halide perovskites were investigated by using first-principles method. The structure-dependent band gap behaviour of tetragonal and pseudocubic MASnxPb1−xI3 (0⩽x⩽1) was emphasized. The configurations with two or more adjacent Sn octahedra in the same layer inducing less tilting of neighbouring octahedra have the lower formation energy. For tetragonal or pseudocubic MASn0.5Pb0.5I3, the configuration of Sn octahedra layer alternating with Pb octahedra layer leads to elongated octahedra along the stacking direction, which stimulates the remarkable band splitting due to anomalous hybridization of Pb or Sn orbitals and I orbitals. This arrangement mode of Sn octahedra produces the narrowest band gap of Sn/Pb binary perovskite, whereas the separated and dispersed Sn octahedra significantly broaden the band gap. The results are helpful to understand the abnormal band gap behaviour in Sn/Pb binary perovskite experiments.

Achieving High-Quality Sn-Pb Perovskite Films on Complementary Metal-Oxide-Semiconductor-Compatible Metal/Silicon Substrates for Efficient Imaging Array.

Although Sn-Pb perovskites sensing near-ultraviolet-visible-near-infrared light could be an attractive alternative to silicon in photodiodes and imaging, there have been no clear studies on such devices constructed on metal/silicon substrates, hindering their direct integration with complementary metal-oxide semiconductor (CMOS) and silicon electronics. Typically, high surface roughness and severe pinholes of Sn-rich binary perovskites make it difficult for them to fulfill the requirements of efficient photodiodes and imaging. These issues cause inherently high dark current and poor (dark and photo-) current uniformity. Herein, we propose and demonstrate the room-temperature crystallization in the Sn-rich binary perovskite system to effectively control film crystallization kinetics. With experimental and theoretical studies of the crystallization mechanism, we successfully tune the density and location of nanocrystals in precursor films to achieve compact nanocrystals, which coalesce into high-quality (smooth, dense, and pinhole-free) perovskites with intensified preferred orientation and decreased trap density. The high-quality perovskites reduce dark current and improve (dark and photo-) current uniformity of perovskite photodiodes on CMOS-compatible metal/silicon substrates. Meanwhile, self-powered devices achieve a high responsivity of 0.2 A/W at 940 nm, a large dynamic range of 100 dB, and a fast fall time of 2.27 μs, exceeding those of most silicon-based imaging sensors. Finally, a 6 × 6 pixel integrated photodiode array is successfully demonstrated to realize the imaging application. The work contributes to understanding the fundamentals of the crystallization of Sn-rich binary perovskites and advancing perovskite integration with Si-based electronics.

Sn‐Pb Binary Perovskite Films with High Crystalline Quality for High Performance Solar Cells

Summary of main observation and conclusionAs an environmentally friendly perovskite material with low bandgap, Tin (Sn)‐based perovskite has drawn much attention. A simple and effective method for fabricating high‐quality Sn‐Pb binary perovskite film is highly desired. Here, with methylammonium chloride (MACl) post‐treatment to assist vertical recrystallization, we fabricated high quality FA0.75Cs0.25Pb0.5Sn0.5I3 perovskite film via one‐step processing method. This recrystallization method was first used in Sn‐based perovskite. The obtained film consists of vertically aligned grains with high crystallinity, which contributes to a power conversion efficiency (PCE) of 14.03% in corresponding perovskite solar cell (PVSC). The cells maintained 80% of their initial PCEs after being stored for 30 d in glove‐box. This simple, effective method provides an easy way to fabricate high performance Sn‐Pb binary PVSC.

Excitation dynamics of MAPb(I1-xBrx)3 during phase separation by photoirradiation: Evidence of sink, band filling, and Br-Rich phase coarsening

Here, we report the radiative recombination behavior of a binary perovskite, MAPb(I0.2Br0.8)3, during phase separation by investigating photoluminescence (PL) spectrum modulations under different laser irradiation conditions: power density, wavelength (379 and 470 nm), and irradiation time. During laser irradiation, the original PL spectrum was divided into three PL peaks assigned to the 1st I-rich, 2nd I-rich, and Br-rich phases. The observed modulations of the intensity and wavelength of the PL spectrum could be explained by the multiple effects of the charge carrier sink, band filling, and Br-rich phase coarsening. Under a weak laser power density, the observed PL predominantly showed the sink effects of the charge carriers through the excited state potential minimum. As the laser power density or irradiation time increased, new high-energy PL bands appeared owing to the band filling and Br-rich phase formation. With a further increase in the laser power or irradiation time, the PL from the Br-rich phase was intensified, but its PL peak position was red-shifted owing to the quantum size effect from the Br-rich phase coarsening. These variations in PL intensity and charge carrier behavior were carefully studied using time- and space-resolved fluorescence imaging microscopy.

Improved Efficiency and Stability of Pb/Sn Binary Perovskite Solar Cells Fabricated by Galvanic Displacement Reaction

AbstractHere, a simple and generally applicable method of fabricating efficient and stable Pb‐Sn binary perovskite solar cells (PVSCs) based on a galvanic displacement reaction (GDR) is demonstrated. Different from the commonly used conventional approaches to form perovskite precursor solutions by mixing metal halides and organic halides such as PbI2, SnI2, MAI, FAI, etc., together, the precursor solutions are formulated by reacting pure Pb‐based perovskite precursor solutions with fine Sn metal powders. After the ratios between Pb and Sn are optimized, high PCEs of 15.85% and 18.21% can be achieved for MAPb0.4Sn0.6I3 and (FAPb0.6Sn0.4I3)0.85(MAPb0.6Sn0.4Br3)0.15 based PVSCs, which are the highest PCEs among all values reported to date for Pb‐Sn binary PVSCs. Moreover, the GDR perovskite‐based PVSCs exhibit significantly improved ambient and thermal stability with encapsulation, which can retain more than 90% of their initial PCEs after being stored in ambient (relative humidity (RH) ≈50%) for 1000 h or being thermal annealed at 80 °C for more than 120 h in ambient conditions. These results demonstrate the advantage of using GDR to prepare tunable bandgap binary perovskites for devices with greatly improved performance and stability.

3D low toxicity Cu–Pb binary perovskite films and their photoluminescent/photovoltaic performance

The 3D low-toxic Cu–Pb binary perovskite films with improved geometric symmetry and typical 2 μm grain size have been prepared, which can achieve a six fold increase in PL intensity and a PCE of 5.1% with suppressed hysteresis for planar solar cells.

Highly Efficient Sn/Pb Binary Perovskite Solar Cell via Precursor Engineering: A Two‐Step Fabrication Process

AbstractRegulation of the crystallization of perovskite films and avoiding the oxidation of Sn2+ during the deposition process are very important for achieving Sn/Pb binary perovskite solar cells (PVSCs) with high power conversion efficiency (PCE) and producibility. In this work, a high‐quality HC(NH2)2Pb0.7Sn0.3I3 (FAPb0.7Sn0.3I3) film deposited from the two‐step solution process by introducing methylammonium thiocyanate (MASCN) as a bifunctional additive into the precursor solution containing PbI2 and SnI2 is reported. MASCN can not only tune the morphology of the perovskite film but also stabilize the precursor solution via retarding the oxidation of Sn2+ through a strong coordination between SCN− and Sn2+. The Sn/Pb binary inverted PVSCs based on FAPb0.7Sn0.3I3 present a high fill factor of 0.79 and the best PCE of 16.26% in the case of 0.25 MASCN addition. The device fabrication producibility is also greatly improved due to the stabilized precursor solution with the aid of MASCN. The PCE of the device is almost independent of the storage time of the precursor solution within 124 d in the N2‐filled glove box. These results indicate that the precursor engineering with multifunctionality additive is an effective approach toward highly efficient and producible PVSCs for future commercialization.

Organic-inorganic hybrid Sn-based perovskite photodetectors with high external quantum efficiencies and wide spectral responses from 300 to 1000 nm

Organic-inorganic hybrid perovskites are ideal materials for photodetection owing to their high charge carrier mobility, long charge carrier diffusion length, low dark current density and sharp absorption edge. However, a relatively small band gap (1.6 eV) limits their photon-harvesting efficiency in the near-infrared region. In the present work, we demonstrate a hybrid methylamine iodide and Pb-Sn binary perovskite as the light absorption layer in photodetectors. Experimentally, the wavelength of photoresponse onset for the photodetectors can be extended to as great as 1,000 nm when the Sn content of the hybrid perovskite is increased to 30 mol%. In addition, the photodetectors exhibit a photoresponsivity of 0.39 A W−1, a specific detectivity of 7×1012 Jones, a fast photoresponse with rise and decay time constants and an external quantum efficiency greater than 50% in the wavelength range of 350–900 nm, with a maximum value of about 80% at 550 nm.

Multiferroicity and magnetoelastic coupling in α−Mn2O3 : A binary perovskite

Multiferroics where at least two primary ferroic orders are present and coupled in a single system constitute an important class of materials. They attracted special consideration as they present both intriguing fundamental physics problems and technological importance for potential multifunctional devices. Here, we present the evidence of multiferroicity and magnetoelectric (ME) coupling in alpha-Mn2O3; a unique binary perovskite. Corresponding to the antiferromagnetic (AFM) ordering around 80K, a clear frequency independent transition is observed in the dielectric permittivity. We showed that electric polarization emerges near AFM regime that can be modulated with magnetic field. The detailed structural analysis using synchrotron radiation X-ray diffraction demonstrates the increase in structural distortion with decreasing temperature, as well as changes in the unit cell parameters and bond lengths across the ferroelectric and magnetic ordering temperatures. This observation of multiferroicity and magnetoelastic coupling in alpha-Mn2O3 provides insights for the exploration of ME coupling in related materials.

Spin-induced multiferroicity in the binary perovskite manganite Mn2O3

The ABO3 perovskite oxides exhibit a wide range of interesting physical phenomena remaining in the focus of extensive scientific investigations and various industrial applications. In order to form a perovskite structure, the cations occupying the A and B positions in the lattice, as a rule, should be different. Nevertheless, the unique binary perovskite manganite Mn2O3 containing the same element in both A and B positions can be synthesized under high-pressure high-temperature conditions. Here, we show that this material exhibits magnetically driven ferroelectricity and a pronounced magnetoelectric effect at low temperatures. Neutron powder diffraction revealed two intricate antiferromagnetic structures below 100 K, driven by a strong interplay between spin, charge, and orbital degrees of freedom. The peculiar multiferroicity in the Mn2O3 perovskite is ascribed to a combined effect involving several mechanisms. Our work demonstrates the potential of binary perovskite oxides for creating materials with highly promising electric and magnetic properties.

Mixed-halide Pb-Sn binary perovskite films with various Sn-content for Pb-reduced solar cells

We proposed and examined a material group of methylammonium Pb-Sn mixed halide (MAPb1−xSnxI2.6Br0.4) with various Sn-content (x = 0.2–0.8) for Pb-reduced perovskite solar cells. With suitable Pb-Sn ratio (x = 0.4–0.6), dense coverage of films with better crystallinity was obtained compared with low Sn ratio (x = 0.2). For excess Sn ratio (x = 0.8), poor film-uniformity was found in spite of its enhanced crystallinity. Optimum composition (x = 0.6) provided an impressive power conversion efficiency of 13.4% with remarkable photocurrent output stability, which is related to suppression of trap-assisted recombination regarding the perovskite materials. This promising material paves the way for development of highly efficient, Pb-reduced perovskite photovoltaic cells.