Hybrid Lead Halide Research Articles

Influence of Cl Incorporation in Perovskite Precursor on the Crystal Growth and Storage Stability of Perovskite Solar Cells.

Solar cells based on organic-inorganic hybrid lead-halide perovskites are very promising because of their high performance and solution process feasibility. Elemental engineering on perovskite composition is a facile path to obtain high-quality crystals for efficient and stable solar cells. It was found that partially substituting I- with Cl- in the perovskite precursor promoted crystal growth, with the grain size larger than the layer thickness, and facilitated the generation of a self-passivation layer of PbI2. Whereas the residual Cl- ions were suspected to diffuse to the hole-transport layer consisting of ubiquitously spiro-OMeTAD, the formation of highly bounded ionic pairing of Cl- with the oxidized state of spiro-OMeTAD led to insufficient charge extraction and severely reversible performance degradation. This issue was effectively alleviated upon Br- doping owing to the generation of Pb-Br bonds in the lattice that strengthened the phase stability by improving the binding energy between each unit. The binary halide (Br-/Cl-)-doped perovskites resulted in a champion power conversion efficiency of 20.2% with improved long-term storage stability.

Fe2+/Fe3+ Doped into MAPbCl3 Single Crystal: Impact on Crystal Growth and Optical and Photoelectronic Properties

As one type of organic–inorganic hybrid lead halide perovskites, MAPbX3 has attracted immense interests in applications of optoelectronic devices because of its remarkable properties. However, the ...

Enhanced Seebeck Effect of a MAPbBr3 Single Crystal by an Organic and a Metal Modified Layer

AbstractThe organic–inorganic hybrid lead halide perovskite single crystal has drawn much attention of researchers for excellent characteristics, such as more excellent stability than the polycrystalline film. However, during the crystal preparation process, there are inevitably generated surface defect states, which seriously affect the charge transport properties of the single crystal. In this article, the MAPbBr3 single crystal is prepared by the inverse temperature crystallization method, the semiconductor characteristics of the crystal surface defect states are studied by the Seebeck effect method, and the crystal Seebeck coefficient is enhanced. It is confirmed that there are N‐type defect states on the surface of the MAPbBr3 single crystal. Then the organic semiconductor layer and metal surface modified layer are utilized to reduce the concentration of defects and got the enhancement of the Seebeck coefficient of MAPbBr3 single crystal. At last, the Au/MAPbBr3/PFO/Au structure device is designed and prepared to improve the thermoelectric properties of the MAPbBr3 single crystal. Results show that the thermal voltage keeps increasing, and the Seebeck coefficient is also enhanced.

Organic cation directed hybrid lead halides of zero-dimensional to two-dimensional structures with tunable photoluminescence properties

A series of new inorganic–organic hybrid lead halides have been solvothermally synthesized and characterized with tunable luminescence properties from yellow, orange to red emissions with the largest reported Stokes shift.

Patterned films of a hybrid lead halide perovskite grown using space-confined conversion of metallic lead by reactive polyiodide melts.

A unique technique for preparation of thin patterned perovskite films is suggested based on an interaction of reactive polyiodide melts with metallic lead coatings using a patterned die with a given relief. The growth of perovskite in confined space results in pin-hole free textured films.

Environmentally Benign All-inorganic Perovskite Solar Cells

Organic/inorganic hybrid lead halide perovskite solar cells have recently emerged as the forerunner in the next generation of photovoltaic technology due to unprecedented progress in power conversion efficiency from their debut of 3.8% in 2009 to the currently certified 23.3%. Mixed PSC solar cells are subject to compositional degradation when exposed to ambient surroundings, which thwarts their real-world applications. Moreover, lead-based compounds pose environmental/health hazards. Very recently, all-inorganic lead-free perovskites have attracted enormous attention because this type successfully dismantles two roadblocks—instability and toxicity, which would accelerate the commercialization. In this outlook, we offered our perspective on the most recent developments in material sciences of halides all inorganic perovskites with possible alternatives to lead, the synthesis approaches, assessment of various device configurations and their progress in solar cells. For the sake of comparison, we also reviewed some all-inorganic but lead-based counterparts in order to motivate researchers to explore all the potentials. Surveying recent developments toward lead-free all-inorganic perovskite solar cells would offer a roadmap for developing new materials and navigate uncharted territory in solar energy fields.

PbX2(OOCMMIm) (X = Cl, Br): photoluminescent organic-inorganic hybrid lead halide compounds with high proton conductivity.

Differences in the electronegativity and hydrophilicity of halogens lead to differences in proton-conducting and photoluminescence properties in hybrid organic-inorganic lead halide compounds of [PbX2(OOCMMIm)]n (X = Cl (1), Br (2), HOOCMMIm = 1-carboxymethyl-3-methylimidazolium).

Mixed phononic and non-phononic transport in hybrid lead halide perovskites: glass-crystal duality, dynamical disorder, and anharmonicity

First-principles and classical modeling reveal a glass-crystal duality in the nature of vibrational transport in lead halide hybrid perovskites.

Melting temperature suppression of layered hybrid lead halide perovskites via organic ammonium cation branching.

Hybrid organic-inorganic lead halide perovskites have attracted broad interest because of their unique optical and electronic properties, as well as good processability. Thermal properties of these materials, often overlooked, can provide additional critical information for developing new methods of thin film preparation using, for example, melt processing-i.e., making films of hybrid perovskites by solidification of a thin layer of the melt liquid. We demonstrate that it is possible to tune the melting temperature of layered hybrid lead iodide perovskites over the range of more than 100 degrees by modifying the structures of alkylammonium-derived organic cations. Through the introduction of alkyl chain branching and extending the length of the base alkylammonium cation, melting temperatures of as low as 172 °C can be achieved and high quality thin films of layered hybrid lead iodide perovskites can be made using a solvent-free melt process with no additives and in ambient air. Additionally, we show that a similar concept can be translated to the corresponding layered bromides, with slightly higher observed melting temperatures. The design rules established here can guide the discovery of new melt-processable perovskite materials for low-cost high performance devices.

Tuning the bandgap of Cs2AgBiBr6 through dilute tin alloying

The promise of lead halide hybrid perovskites for optoelectronic applications makes finding less-toxic alternatives a priority. The double perovskite Cs2AgBiBr6 (1) represents one such alternative, offering long carrier lifetimes and greater stability under ambient conditions. However, the large and indirect 1.95 eV bandgap hinders its potential as a solar absorber. Here we report that alloying crystals of 1 with up to 1 atom% Sn results in a bandgap reduction of up to ca. 0.5 eV while maintaining low toxicity. Crystals can be alloyed with up to 1 atom% Sn and the predominant substitution pathway appears to be a ∼2 : 1 substitution of Sn2+ and Sn4+ for Ag+ and Bi3+, respectively, with Ag+ vacancies providing charge compensation. Spincoated films of 1 accommodate a higher Sn loading, up to 4 atom% Sn, where we see mostly Sn2+ substitution for both Ag+ and Bi3+. Density functional theory (DFT) calculations ascribe the bandgap redshift to the introduction of Sn impurity bands below the conduction band minimum of the host lattice. Using optical absorption spectroscopy, photothermal deflection spectroscopy, X-ray absorption spectroscopy, 119Sn NMR, redox titration, single-crystal and powder X-ray diffraction, multiple elemental analysis and imaging techniques, and DFT calculations, we provide a detailed analysis of the Sn content and oxidation state, dominant substitution sites, and charge-compensating defects in Sn-alloyed Cs2AgBiBr6 (1:Sn) crystals and films. An understanding of heterovalent alloying in halide double perovskites opens the door to a wider breadth of potential alloying agents for manipulating their band structures in a predictable manner.

Lead-free, stable, and effective double FA4GeIISbIIICl12 perovskite for photovoltaic applications

Organic-inorganic hybrid lead halide perovskite solar cells emerge as a breakthrough photovoltaic technology with high power conversion efficiency. However, some inherent shortcomings impede their further industrialization: 1) the toxicity of Pb, 2) unstable, sensitive to moisture and/or light. To circumvent these issues, we study the lead-free and solution-processed photovoltaic devices based on the double-metals <111>-oriented 2D layered formamidinium germanium-antimony halide perovskites (FA4GeIISbIIICl12) in this contribution. Compared with benchmark MAPbI3, the larger formamidinium is selected to replace methylammonium to form a more stable crystal structure while the double metals germanium-antimony (GeII-SbIII) are chosen to replace Pb under the considerations that expanding the possible metal combinations in the design of new perovskite with analogous photovoltaic performance. The FA4GeIISbIIICl12 perovskite behaves as a stable and efficient semiconductor with direct bandgap of ~ 1.3 eV and its conductivity is one order of magnitude higher than that of MAPbI3. Meanwhile, FA4GeIISbIIICl12 based solar cell with power conversion efficiency up to 4.7% can be achieved without use of any additives. This approach opens up new possibilities of exploiting lead-free perovskite that incorporates metals in different valence states and offers great potential application in photoelectric field.

Lifetime-shortened acoustic phonons and static order at the Brillouin zone boundary in the organic-inorganic perovskite CH3NH3PbCl3.

Lead halide hybrid perovskites consist of an inorganic framework hosting a molecular cation located in the interstitial space. These compounds have been extensively studied as they have been identified as promising materials for photovoltaic applications with the interaction between the molecular cation and the inorganic framework implicated as influential for the electronic properties. CH3NH3PbCl3 undergoes two structural transitions from a high temperature cubic unit cell to a tetragonal phase at 177 K and then a subsequent orthorhombic transition at 170 K. We have measured the low-frequency lattice dynamics using neutron spectroscopy and observe an energy broadening in the acoustic phonon linewidth towards the high-symmetry point when approaching the transitions. Concomitant with these zone boundary anomalies is a hardening of the entire acoustic phonon branch measured in the limit near the (2, 0, 0) Bragg position with decreasing temperature. Measurements of the elastic scattering at the Brillouin zone edges , and show Bragg peaks appearing below these structural transitions. Based on selection rules of neutron scattering, we suggest that the higher 177 K transition is displacive with a distortion of the local octahedral environment and the lower transition is a rigid tilt transition of the octahedra. We do not observe any critical broadening in energy or momentum, beyond resolution, of these peaks near the transitions. We compare these results to the critical properties reported near the structural transitions in other perovskites and particularly CsPbCl3 [Y. Fujii, S. Hoshino, Y. Yamada, and G. Shirane, Phys. Rev. B 9, 4549 (1974)]. We suggest that the simultaneous onset of static resolution-limited Bragg peaks at the zone boundaries and the changes in acoustic phonon energies near the zone center is evidence of a coupling between the inorganic framework and the molecular cation. The results also highlight the importance of displacive transitions in organic-inorganic hybrid perovskites.

Impact of Organic Spacers on the Carrier Dynamics in 2D Hybrid Lead-Halide Perovskites

We have carried out nonadiabatic molecular dynamics simulations combined with time-dependent density functional theory calculations to compare the properties of the two-dimensional (2D) (BA)2(MA)Pb2I7 and three-dimensional (3D) MAPbI3 (where MA = methylammonium and BA = butylammonium) materials. We evaluate the different impacts that the 2D-confined spacer layer of butylammonium cations and the 3D-confined methylammonium cations have on the charge carrier dynamics in the two systems. Our results indicate that, while both the MA+ and BA+ cations play important roles in determining the carrier dynamics, the BA+ cations exhibit stronger nonadiabatic couplings with the 2D perovskite framework. The consequence is a faster hot-carrier decay rate in 2D (BA)2(MA)Pb2I7 than in 3D MAPbI3. Thus, tuning of the functional groups of the organic spacer cations in order to reduce the vibronic couplings between the cations and the Pb–I framework can offer the opportunity to slow down the hot-carrier relaxations and increa...

Screening Approach for the Discovery of New Hybrid Perovskites with Efficient Photoemission

AbstractOwing to quantum confinement, low‐dimensional hybrid perovskite materials have recently shown a great potential for applications in optoelectronics. Such compounds can exhibit broad‐ or narrow‐band light emission, low‐temperature solution processability, high thermal stability, and relatively high photoluminescence quantum yields (PLQY). However, the search for efficient phosphors with a specific set of characteristics remains difficult because the family of hybrid perovskites consists in an extremely large chemical system (i.e., different halides, metals, and organic molecules), and optical properties are not predictable prior to material synthesis and characterization. Here, is proposed a simple approach to screen a significant amount of new hybrid lead halide perovskites. The synthetic method by fast crystallization at low temperature enables the rapid identification of the materials exhibiting the targeted photoluminescence properties. This approach is tested for the discovery of hybrid lead halide perovskites with efficient white‐light emission. Among 100 newly synthesized compounds, 5 exhibit intense white emission, and the in‐depth characterization of a selected candidate shows high color rendering index (CRI) = 78 and a PLQY of 9%, which is equivalent to the record reported for hybrid perovskites. This compound exhibits a new structure type for warm white‐light emitting hybrid perovskites with chains of corner‐sharing PbX6.

Carrier cascade: Enabling high performance perovskite light-emitting diodes (PeLEDs)

In recent years, hybrid lead-halide perovskites have emerged as promising solution-processed semiconductors for thin-film optoelectronics with a growing focus on light-emitting diode applications. Perovskites exhibit remarkable flexibilities in structure and composition tuning and possess excellent intrinsic properties such as band gap tunability over a visible range, high colour purity emission, high photoluminescence quantum yield (PLQY) and high exciton binding energies. Recently, perovskite-based light-emitting diodes (PeLEDs) have exhibited external quantum efficiency of 14.36% and revealed the potential for further improvement. High PLQY is a key requirement for better PeLED performance. This can be realised by controlling the grain-size of the perovskite films with optimum active layer thickness and utilising reduced-dimensionality perovskite emitters to spatially confine charge carriers for enhanced radiative recombination. In this short review, we discuss the critical parameters required for efficient PeLEDs, the recent progress mainly highlighting the energy transfer mechanism within Ruddlesden Popper structures and graded size nanoparticle films. We also outline the recommendations and strategies for further improvement.

PIN Diodes Array Made of Perovskite Single Crystal for X‐Ray Imaging

Recently, lead (Pb) halide hybrid perovskites have emerged as sensitive X‐ray detectors due to their desirable charge transport properties and high absorption of ionizing photons. This work reports on a facile methodology for fabrication of highly efficient X‐ray PIN diodes based on MAPbBr3 (MA, methylammonium; Pb, lead; Br, bromide) single crystals to detect X‐ray energies ranging from 30 to 100 keV. The 2 mm thickness PIN diode exhibits a low dark current density of 20 nA cm−2 at 150 V cm−1 and high X‐ray sensitivity of 23.6 μC mGyair−1 cm−2. Besides, a large‐area array based on 30 mm × 28 mm × 7 mm MAPbBr3 single crystal is fabricated for X‐ray imaging. When augmented with signal processing, selective higher and lower energy X‐ray signals can be separated simultaneously to satisfy different requirements for soft and hard organs and tissues in one exposure. This approach offers a new pathway for a one‐time radiation dose applied to the human body to achieve X‐ray images for tissues and blood vessels concurrently.

Inorganic and Lead-Free AgBiI4 Rudorffite for Stable Solar Cell Applications

Organic–inorganic hybrid lead halide perovskites have recently realized significant development. However, the toxicity of lead (Pb) and the poor stability might eventually hamper the commercialization of perovskite solar cells (PSCs). Here, we present an environment friendly and stable all inorganic rudorffite AgBiI4 as solar absorber by solution-based synthesis of thin-films. AgBiI4 films fabricated by 0.6 M solution and annealed at 150 °C show dense grains and high surface coverage. Furthermore, the AgBiI4 films exhibit greater thermal stability and photostability than CH3NH3PbI3. Ultimately, by judiciously choosing the hole transport material with appropriate energy level, the solar cell device demonstrates high carrier extraction efficiency and achieve a power conversion efficiency (PCE) of 2.1% under standard 1 sun (AM 1.5). The devices also show excellent long-term air stability and still maintain 96% of its initial PCE even after 1000h at relative humidity of 26%. This work highlights new direction...

Elastic Softness of Hybrid Lead Halide Perovskites.

Much recent attention has been devoted towards unraveling the microscopic optoelectronic properties of hybrid organic-inorganic perovskites. Here we investigate by coherent inelastic neutron scattering spectroscopy and Brillouin light scattering, low frequency acoustic phonons in four different hybrid perovskite single crystals: MAPbBr_{3}, FAPbBr_{3}, MAPbI_{3}, and α-FAPbI_{3} (MA: methylammonium, FA: formamidinium). We report a complete set of elastic constants characterized by a very soft shear modulus C_{44}. Further, a tendency towards an incipient ferroelastic transition is observed in FAPbBr_{3}. We observe a systematic lower sound group velocity in the technologically important iodide-based compounds compared to the bromide-based ones. The findings suggest that low thermal conductivity and hot phonon bottleneck phenomena are expected to be enhanced by low elastic stiffness, particularly in the case of the ultrasoft α-FAPbI_{3}.

Flexible and Biocompatibility Power Source for Electronics: A Cellulose Paper Based Hole‐Transport‐Materials‐Free Perovskite Solar Cell

Flexible, biocompatible, and light‐weight power sources are urgently required due to their promising application in wearable electronics. Organic‐inorganic hybrid lead halide perovskite solar cells (PSCs) with their impressive efficiency and scalable processing capability have emerged as promising candidates for efficient and reliable power sources for wearable electronics. However, the progress in developing low‐cost and efficient flexible PSCs has been confined to Poly(ethylene terephthalate) or metal foil substrates and difficulty to design PSCs on other easily accessible low‐cost substrates such as cellulose paper. Herein, the authors report the hole transport material (HTM)‐free flexible PSCs fabricated on abundant, low‐cost, and biocompatible cellulose paper substrate for the first time. The highest PCE of 9.05% for the paper based flexible HTM‐free PSC is achieved and the device could maintain over 75% of its initial PCE after 1000 bending cycles, demonstrating good stability against bending deformation. Our findings provide an avenue to fabricate reliable power source for wearable electronics.

Nanocomposite perovskite based optical sensor with broadband absorption spectrum

Recently, organic-inorganic hybrid lead halide perovskite optical sensors have attracted lots of attention for their unique and remarkable optoelectronic properties like low-cost solution process deposition. Also, inorganic nanoparticles with narrow bandgap as photocarrier generator has been used in high efficiency low cost optical sensors to increase absorption spectrum. In this paper, we designed and fabricated a solution processed optical sensor by using nanocomposite of Methylammonium lead iodide and PbS nanoparticles as the active layer. It has high absorption in the broad range of spectrum that can work in small driving voltages (less than 1 V). It has low dark current and high photocurrent that are important parameters in optical sensors. This device achieves excellent photoresponsivity and high external quantum efficiency for broad range of wavelength from 370 nm to 940nm.