Hybrid Lead Halide Perovskites Research Articles

Single-Source Vapor-Deposited Cs2AgBiBr6 Thin Films for Lead-Free Perovskite Solar Cells.

Lead-free double perovskites have been considered as a potential environmentally friendly photovoltaic material for substituting the hybrid lead halide perovskites due to their high stability and nontoxicity. Here, lead-free double perovskite Cs2AgBiBr6 films are initially fabricated by single-source evaporation deposition under high vacuum condition. X-ray diffraction and scanning electron microscopy characterization show that the high crystallinity, flat, and pinhole-free double perovskite Cs2AgBiBr6 films were obtained after post-annealing at 300 °C for 15 min. By changing the annealing temperature, annealing time, and film thickness, perovskite Cs2AgBiBr6 solar cells with planar heterojunction structure of FTO/TiO2/Cs2AgBiBr6/Spiro-OMeTAD/Ag achieve an encouraging power conversion efficiency of 0.70%. Our preliminary work opens a feasible approach for preparing high-quality double perovskite Cs2AgBiBr6 films wielding considerable potential for photovoltaic application.

Effects of alkylamine chain length on perovskite nanocrystals after washing and perovskite light-emitting diodes

Organic–inorganic hybrid lead halide perovskite nanocrystals (PeNCs) have received great attention as a light source for perovskite LEDs (PeLEDs) owing to the superior optical properties. However, PeNCs typically use octylamine (OAm) as capping ligands which have insulating properties. Exploring a desirable short alkylamine instead of OAm is required for the improvement of PeLEDs. Here, as one of the strategies to solve this issue, the effects of alkylamine chain length for optical properties of PeNCs and PeLED characteristics are investigated. Pentylamine is an optimal short alkylamine and precipitate luminescent PeNCs with high PLQY values of 90%. Importantly, pentylamine maintains a relatively high PLQY of 48% after spin-coating, due to the durability pentylamine has to ethyl acetate as a washing solvent. PeNCs capped with pentylamine also demonstrate an external quantum efficiency of over 1% with luminance of over 2000 cd cm−2, indicating that pentylamine has the potential to overcome the insulator properties of PeNC thin film.

Steric Mixed-Cation 2D Perovskite as a Methylammonium Locker to Stabilize MAPbI3.

The reduced dimension perovskite including 2D perovskites are one of the most promising strategies to stabilize lead halide perovskite. A mixed-cation 2D perovskite based on a steric phenyltrimethylammonium (PTA) cation is presented. The PTA-MA mixed-cation 2D perovskite of PTAMAPbI4 can be formed on the surface of MAPbI3 (PTAI-MAPbI3 ) by controllable PTAI intercalation by either spin coating or soaking. The PTAMAPbI4 capping layer can not only passivate PTAI-MAPbI3 perovskite but also act as MA+ locker to inhibit MAI extraction and significantly enhance the stability. The highly stable PTAI-MAPbI3 based perovskite solar cells exhibit a reproducible photovoltaic performance with a champion PCE of 21.16 %. Such unencapsulated devices retain 93 % of initial efficiency after 500 h continuous illumination. This steric mixed-cation 2D perovskite as MA+ locker to stabilize the MAPbI3 is a promising strategy to design stable and high-performance hybrid lead halide perovskites.

Additives in metal halide perovskite films and their applications in solar cells

Abstract The booming growth of organic-inorganic hybrid lead halide perovskite solar cells have made this promising photovoltaic technology to leap towards commercialization. One of the most important issues for the evolution from research to practical application of this technology is to achieve high-throughput manufacturing of large-scale perovskite solar modules. In particular, realization of scalable fabrication of large-area perovskite films is one of the essential steps. During the past ten years, a great number of approaches have been developed to deposit high quality perovskite films, to which additives are introduced during the fabrication process of perovskite layers in terms of the perovskite grain growth control, defect reduction, stability enhancement, etc. Herein, we first review the recent progress on additives during the fabrication of large area perovskite films for large scale perovskite solar cells and modules. We then focus on a comprehensive and in-depth understanding of the roles of additives for perovskite grain growth control, defects reduction, and stability enhancement. Further advancement of the scalable fabrication of high-quality perovskite films and solar cells using additives to further develop large area, stable perovskite solar cells are discussed.

Understanding the Ligand Effects on Photophysical, Optical, and Electroluminescent Characteristics of Hybrid Lead Halide Perovskite Nanocrystal Solids.

There has been a tremendous amount of interest in developing high-efficiency light-emitting diodes (LEDs) based on colloidal nanocrystals (NCs) of hybrid lead halide perovskites. Here, we systematically investigate the ligand effects on EL characteristics by tuning the hydrophobicity of primary alkylamine ligands used in NC synthesis. By increasing the ligand hydrophobicity, we find (i) a reduced NC size that induces a higher degree of quantum confinement, (ii) a shortened exciton lifetime that increases the photoluminescence quantum yield, (iii) a lowering of refractive index that increases the light outcoupling efficiency, and (iv) an increased thin-film resistivity. Accordingly, ligand engineering allows us to demonstrate high-performance green LEDs exhibiting a maximum external quantum efficiency up to 16.2%. The device operational lifetime, defined by the time lasted when the device luminance reduces to 85% of its initial value, LT85, reaches 243 min at an initial luminance of 516 cd m–2.

Dual excitonic emissions and structural phase transition of octylammonium lead iodide 2D layered perovskite single crystal

Two dimensional (2D) layered hybrid lead halide perovskites exhibit interesting electronic and optical properties because of their repeating quantum well structure. These materials are now being explored for various optoelectronic applications, including solar cells and light emitting diodes. But still there are surprises regarding the basic band gap or excitonic absorption and emission of these layered hybrid perovskites. Recently, we showed possibility of dual band gaps or dual excitonic emissions from 2D butylammonium lead iodide (BA2PbI4). In the present paper, we extend the study to octylammonium lead iodide (OA)2PbI4 single crystals. The longer organic cations in (OA)2PbI4 separates the adjacent inorganic Pb-I layers further, reducing any possible electronic interactions between the inorganic layers. Interestingly, (OA)2PbI4 also exhibits dual excitonic emission at room temperature. A minor structural inhomogeneity between near-surface and interior regions of (OA)2PbI4 single crystals might be responsible for the two different excitonic emissions. To explore the correlation between crystal structure and excitonic emissions, we have studied single crystal XRD and photoluminescence at variable temperatures. The results show a small change in tilting of Pb-I6 octahedra can distinctly change the band gap and the excitonic emission energy.

Modulation of Electronic States of Hybrid Lead Halide Perovskite Embedded in Organic Matrix

The modulation of electronic states of MAPbX3 perovskite nanocrystals (PNCs) (MA = CH3NH3+ and X = Br− and I−) is presented as a function of crystallite size in organic semiconductor matrix forming a type‐I heterostructure with bulk perovskites. Organic semiconductor molecule (4,4′‐bis[9‐dicarbazolyl]‐2,2′‐biphenyl [CBP] and bathocuproine [BCP]) precursors are mixed in different volumetric ratios with MAPbX3 perovskite precursors to prepare thin films. This results into an easy growth of MAPbX3 PNCs of tunable sizes from ≈110 to ≈10 nm in organic semiconductor matrix. A blue shift is observed in the photoluminescence peak (PLmax) energy over a range of ≈200 meV for MAPbI3 PNCs embedded in the BCP matrix. However, PLmax energy tunes over ≈32 meV only with a similar volumetric concentration in the case of MAPbBr3 PNCs in the same BCP matrix. Moreover, the PL blue shift is even lower in the case of CBP matrix in comparison with BCP matrix for both the perovskites. This discrepancy could be resolved by determining the resultant crystallite size using X‐ray diffraction studies and the Debye–Scherrer formula. Results about blue shift in the PL peak can be explained using the classic particle‐in‐a‐box versus excitonic Bohr radius model under a weak confinement regime.

Mechanoperovskites for Photovoltaic Applications: Preparation, Characterization, and Device Fabrication.

Hybrid organic-inorganic metal halide perovskites (MHPs) have emerged as excellent absorber materials for next generation solar cells owing to their simple solution-processed synthesis and high efficiency. This breakthrough in photovoltaics along with an accompanying impact in light-emitting applications prompted a renaissance of interest in the broad family of MHPs. Notably, the optoelectronic properties and the photovoltaic parameters of MHPs are highly sensitive to the adopted synthetic strategy. The preparation of MHPs has commonly relied on solution-based methods requiring elevated temperatures for homogeneity of reaction mixtures. While the solution-based approach is relatively versatile, it faces challenges such as limitations in compositional engineering of MHPs or their long-term storage among others. Therefore, there is a continuous great challenge to develop efficient synthetic strategies affording various high-quality MHP materials for numerous technological optoelectronic applications. In the past decade, mechanochemistry has appeared as a green alternative to traditional synthesis. This solid-state, re-emerging efficient synthetic methodology mediated by direct absorption of mechanical energy is growing explosively across organic and inorganic chemistry and materials science. In this Account, we describe our shared interest in the productive use of mechanical force in chemistry of MHPs, as well as assembly of the respective solar cell devices. We highlight the milestones achieved by our groups along with the seminal contributions by other groups. In particular, we demonstrate that mechanochemistry efficiently allows the formation of various phase pure hybrid lead and lead-free halide perovskite compositions (called hereafter "mechanoperovskites"). The progress in solvent-free solid-state synthesis is greatly enhanced by the integration of advanced methods of solid-state analysis like powder X-ray diffraction (pXRD), solid-state nuclear magnetic resonance (ss-NMR) and UV-vis spectroscopies, and we aim to illustrate this ongoing integration through appropriate examples. Furthermore, we show that thin films based on mechanoperovskites have the advantage of providing a higher degree of control of the stoichiometry and higher reproducibility, stability, and material phase purity. The impact of using powdered mechanoperovskite as a precursor for thin film formation on the electrochemical and photovoltaic properties of the solar cells is also discussed. Finally, our view of current challenges and future directions in this emerging interdisciplinary area of research is provided.

Molecularly imprinted polymers and PEG double engineered perovskite: an efficient platform for constructing aqueous solution feasible photoelectrochemical sensor

Herein, a kind of dual polymers, molecularly imprinted polymers (MIPs) and polyethylene glycol (PEG), coated perovskite (MIP-PEG/CH3NH3PbI3) was synthesized and used to construct a photoelectrochemical (PEC) sensor for salicylic acid (SA) detection. A selective MIP layer for SA recognition was anchored on the PEG modified CH3NH3PbI3 through a facile UV-polymerization process. PEG benefits the water-resistant ability of CH3NH3PbI3 and MIPs endows the photoactive CH3NH3PbI3 good selectivity. Thanks to the protection from PEG and MIPs, the MIP-PEG/CH3NH3PbI3 product showed stable photocurrents in aqueous solution. Furthermore, methylammonium iodide (MAI) contained electrolyte was used in which MAI could restore the degraded part of CH3NH3PbI3 to improve its stability. SA was detected by monitoring the photocurrent signal changes of the PEC sensor resulting from the reaction between SA and MIPs. The as-fabricated PEC sensor showed good performance in terms of sensitivity and selectivity. The linear range between the photocurrent changes and the concentrations of SA was from 1.0 × 10-15 to 7.0 × 10-11 M. This work unveiled the promise of organic-inorganic hybrid lead halide perovskite based structure for PEC sensors and inspired more interests in the development of diverse perovskite-based materials for advanced PEC analysis.

Sputtered Transparent Electrodes (IO:H and IZO) with Low Parasitic Near-Infrared Absorption for Perovskite–Cu(In,Ga)Se2 Tandem Solar Cells

Hybrid lead halide perovskite solar cells (PSCs) in tandem application with copper indium gallium diselenide (CIGS) solar cells represent one of the most promising all-thin-film technologies for ne...

Deconstruction-assisted perovskite formation for sequential solution processing of Cs0.15(MA0.7FA0.3)0.85PbI3 solar cells

Organic-inorganic hybrid lead halide perovskite has shown to be one of the best light-harvesting materials for solar cell in the last decade. However, there still is needed a deeper understanding of phase and film formation for better control of device fabrication. In this work, we visualise the formation mechanism of Cs0.15(MA0.7FA0.3)0.85PbI3 perovskite by the sequential spin-coating method and how changes in the dispensing timing and substrate motion affect the formation process and properties of the final film quality. In particular, this is the first time that we are able to visualise and identify the different stages of the film formation: i) “initial formation”; ii) “perovskite deconstruction” and iii) “perovskite re-crystallisation”. This particularly applies to films that are sequentially spin-coated and involve the use of dimethyl sulfoxide (DMSO) as the “deconstruction” is caused by the formation of intermediate-DMSO-complex. These findings are validated by FTIR and XRD measurements. Comparison among processes also suggests that motion causes an earlier onset of deconstruction, which will lead to a slower re-crystallisation resulting in better quality perovskite film with less non-perovskite phase. This can be achieved by motion dispensing and dynamic processing (where there is no stoppage between the two sequential steps). Reasons for the earlier onset of deconstruction are the higher kinetic energy supplied by the dynamic process. This work has provided more insights into the complex stages involved in perovskite conversion specific to sequential processing. The knowledge will aid future process optimisation for better device fabrication.

Common acoustic phonon lifetimes in inorganic and hybrid lead halide perovskites

The acoustic phonons in the organic-inorganic lead halide perovskites have been reported to have anomalously short lifetimes over a large part of the Brillouin zone. The resulting shortened mean free paths of the phonons have been implicated as the origin of the low thermal conductivity. We apply neutron spectroscopy to show that the same acoustic phonon energy linewidth broadening (corresponding to shortened lifetimes) occurs in the fully inorganic CsPbBr3 by comparing the results on the organic-inorganic CH3NH3PbCl3. We investigate the critical dynamics near the three zone boundaries of the cubic Brillouin zone of CsPbBr3 and find energy and momentum broadened dynamics at momentum points where the Cs-site (A-site) motions contribute to the cross section. Neutron diffraction is used to confirm that both the Cs and Br sites have unusually large thermal displacements with an anisotropy that mirrors the low temperature structural distortions. The presence of an organic molecule is not necessary to disrupt the low-energy acoustic phonons at momentum transfers located away from the zone center in the lead halide perovskites and such damping may be driven by the large displacements or possibly disorder on the A site.

Enhanced Electrons Extraction of Lithium-Doped SnO$_{2}$ Nanoparticles for Efficient Planar Perovskite Solar Cells

Hybrid lead halide perovskite solar cells (PSCs) are amongst those efficient solar cell technologies which are developing rapidly. The rapid advancement in PSCs technology is because of favorable properties of perovskite materials and addition of charge selective layers. Here, we report lithium-doped SnO $_{2}$ electron transport layer (ETL) to improve electrons extraction from the perovskite absorbing layer. The lithium-doped SnO $_{2}$ not only shows relatively higher conductivity, reduced oxygen-deficient regions, improved oxidation state, but also induces a larger grain size of perovskite films. This leads to an improvement in all related photovoltaic parameters of the methylammonium lead iodide (MAPbI3) planar heterojunction PSCs. The champion device yields a power conversion efficiency of 19.09%. The simple solution and lower annealing processed ETLs are compatible with almost all substrates used in PSCs and other perovskite-based devices.

Lead-Free Antimony-Based Light-Emitting Diodes through the Vapor-Anion-Exchange Method.

Hybrid lead halide perovskites continue to attract interest for use in optoelectronic devices such as solar cells and light-emitting diodes. Although challenging, the replacement of toxic lead in these systems is an active field of research. Recently, the use of trivalent metal cations (Bi3+ and Sb3+) that form defect perovskites A3B2X9 has received great attention for the development of solar cells, but their light-emissive properties have not previously been studied. Herein, an all-inorganic antimony-based two-dimensional perovskite, Cs3Sb2I9, was synthesized using the solution process. Vapor-anion-exchange method was employed to change the structural composition from Cs3Sb2I9 to Cs3Sb2Br9 or Cs3Sb2Cl9 by treating CsI/SbI3 spin-coated films with SbBr3 or SbCl3, respectively. This novel method facilitates the fabrication of Cs3Sb2Br9 or Cs3Sb2Cl9 through solution processing without the need of using poorly soluble precursors (e.g., CsCl and CsBr). We go on to demonstrate electroluminescence from a device employing Cs3Sb2I9 emitter sandwiched between ITO/PEDOT:PSS and TPBi/LiF/Al as the hole and electron injection electrodes, respectively. A visible-infrared radiance of 0.012 W·Sr-1·m-2 was measured at 6 V when Cs3Sb2I9 was the active emitter layer. These proof-of-principle devices suggest a viable path toward low-dimensional, lead-free A3B2X9 perovskite optoelectronics.

Energetics of Solvent-Based Deposition of Fullerene Derivative on the Inorganic–Organic Hybrid Lead Halide Perovskite Surface

The elementary processes that govern particle deposition on substrates during solution processing of thin films are not well understood due to the complex interactions between solute–solvent, solute–substrate, and solvent–substrate. This study presents a fundamental step-by-step systematic analysis of the deposition of a rather complex molecule, the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), with seemingly infinite orientational configurations, on the (110) surface of methylammonium lead iodide (CH3NH3PbI3) perovskite in a solvated environment. We employed the adaptive biasing force (ABF) method in conjunction with classical molecular dynamics (MD) simulations to determine the potential of mean force (PMF) and corresponding configurations of deposited PCBM in the presence of chlorobenzene (CB) and vacuum. Our calculations underscore the impact of solvent on the energetics of deposition and the resulting configurations of deposited PCBM. In the presence of solvent, the most energetically favorable ...

Lead-Halide Perovskites Meet Donor–Acceptor Charge-Transfer Complexes

Low-dimensional lead halide hybrid perovskites are nowadays in the spotlight because of their improved stability and extensive chemical flexibility compared to their 3D perovskite counterparts, the...

A Lead-Free Hybrid Iodide with Quantitative Response to X-ray Radiation

Single crystals of lead halide hybrid perovskites (e. g., CH3NH3PbI3 and CsPbBr3) have been developed as promising candidates for X-ray detection, owing to their excellent attributes including low ...

Prospects for the use of carbon-based perovskite solar cells

For the first time, perovskite solar cells were demonstrated in 2009, and since then have been the subject of intense study. Due to the fact that perovskite has a band gap zone with direct transitions, it absorbs light more efficiently than silicon, and a thin layer is required to produce a solar cell, which can be obtained by precipitation from solution, which significantly reduces the cost of production of perovskite solar cells. Recently organic-inorganic hybrid lead-halide perovskite solar cells (PSCs) achieved a certified energy conversion efficiency of 23.7%. Among the various types of PSCs, carbon-based hole-conductor-free perovskite solar cells (CPSCs) were gradually recognized as the most promising for the commercialization with the advantages of low cost, high stability and easy fabrication. Here we review the latest developments in the field of printable carbon-based hole-conductor-free perovskite solar cells.

Supramolecular Coordination of Pb2+ Defects in Hybrid Lead Halide Perovskite Films Using Truxene Derivatives as Lewis Base Interlayers.

Truxene derivatives, due to their molecular structure and properties, are good candidates for the passivation of defects when deposited onto hybrid lead halide perovskite thin films. Moreover, their semiconductor characteristics can be tailored through the modification of their chemical structure, which allows-upon light irradiation- the interfacial charge transfer between the perovskite film and the truxene molecules. In this work, we analysed the use of the molecules as surface passivation agents and their use in complete functional solar cells. We observed that these molecules reduce the non-radiative carrier recombination dynamics in the perovskite thin film through the supramolecular complex formation between the Truxene molecule and the Pb2+ defects at the perovskite surface. Interestingly, this supramolecular complexation neither affect the carrier recombination kinetics nor the carriers collection but induced noticeable hysteresis on the photocurrent vs voltage curves of the solar cells under 1 sun illumination.

Giant Enhancement of Photoluminescence Emission in WS2-Two-Dimensional Perovskite Heterostructures.

Transition metal dichalcogenides (TMDCs) and two-dimensional organic and inorganic hybrid lead halide perovskites (2DPVSKs) have emerged as highly promising materials for ultralight and ultrathin optoelectronics application. They both exhibit tunability of electronic properties such as band structure, and they can form heterostructures with various types of two-dimensional materials for novel physical properties not observed in single components. However, TMDCs exhibit poor emission efficiency due to defect states and direct-to-indirect interband transition, and 2DPVSKs suffer from poor stability in ambient atmosphere. Here we report that fabrication of TMDC-on-2DPVSK heterostructures using a solvent-free process leads to novel optical transitions unique to the heterostructure which arise from the hybrid interface and exhibit a strong photoluminescence. Moreover, a two orders of magnitude enhancement of the photoluminescence as compared to WS2 emission is observed. The TMDC on top of 2DPVSK also significantly improves the stability as compared to bare 2DPVSK. Enhanced emission can be explained by electronic structure modification of TMDC by novel interfacial interactions between TMDC and 2DPVSK materials, which shows promise of the heterostructure for high efficiency and stable optoelectronic devices.