Perovskite Crystal Growth Research Articles

Temperature effects on surface textures of CsPbIBr2 films for perovskite solar cells

The quality of perovskite crystallization directly determines the performance of perovskite solar cells (PSCs). However, there is a lack of research on the bottom crystallization of perovskite films of PSCs. Here, by simply controlling the annealing temperature of perovskite films, CsPbIBr2 films with different surface textures on both the top and bottom sides were obtained, respectively. It is found that dimethyl sulfoxide (DMSO), which is widely used to enhance the crystallization of perovskite films, cannot be completely removed under 160 °C, leading to the formation of snowflower-like textures (SFT) composed of countless pinholes on the upper and lower surfaces of the perovskite film and the existence of obvious cavities between the perovskite layer and the TiO2 layer. This is mainly due to the dissolution of CsPbIBr2 in the residual DMSO. On the contrary, CsPbIBr2 films with compact and smooth surface textures (CST) on both the top and bottom sides can be achieved under 250 °C. For PSCs, the CST-based champion device (9.66%) exhibits higher efficiency and better stability than the SFT-based one (3.69%), primarily due to the high quality film with superior carrier separation and migration properties. The proposed understanding and accurate control of the perovskite crystal growth process are of great significance to the future development of PSCs.

Modulated crystal growth enables efficient and stable perovskite solar cells in humid air

The preparation of high-quality perovskite thin film in ambient air is crucial for achieving low-cost commercialization of perovskite solar cells (PSCs). However, it is difficult to obtain high-performance PSCs in high-humidity atmosphere because the perovskite films based on universal PbI2 lead source face the challenges of sluggish crystallization rate and high defect density. Herein, we report an effective additive method by incorporating volatile methylamine salts into the perovskite precursor solution to facilitate the fabrication of efficient and stable MAPbI3 PSCs in ambient air irrespective of the humidity. The addition of various compositional volatile methylamine salts (MACl, MASCN and MAAc) can modulate perovskite crystal growth in different degrees and improve the film quality with enhanced crystallinity and enlarged crystal grains. By comparison, the device with MACl additive achieves the highest power conversion efficiency (PCE) of 20.06% with almost no hysteresis owing to the significantly reduced defect state density in the film. Meanwhile, the device with MASCN addition delivers the second-best PCE (19.19%). Notably, the according perovskite film exhibits the strongest crystallinity that renders excellent photovoltaic performance even in ultrashort annealing duration or without annealing, indicating a prospect for the rapid upscaling of PSCs in ambient air. Furthermore, the PSCs without encapsulation show greatly enhanced air stability after the film growth modulation. Our work demonstrates the possibility of fabricating efficient and stable PSCs in humid atmosphere with PbI2 lead source and should be informative for industrial production in the future.

Additive Engineering in Antisolvent for Widening the Processing Window and Promoting Perovskite Seed Formation in Perovskite Solar Cells.

The chlorobenzene (CB) antisolvent is widely used to fabricate high-efficiency perovskite solar cells (PSCs). However, the narrow processing window and the strict volume ratio of a binary mixed solvent limit the fabrication of large-area and high-quality perovskite films. In this work, by systematic investigation of additives with the CB antisolvent, a universal guideline is achieved wherein a small amount of additive with a donor number between 9.0 and 27.0 kcal/mol can significantly widen the antisolvent treating time slot from 2 to 40 s while simultaneously enlarging the processor binary mixed solvent (dimethylformamide/dimethyl sulfoxide) from 7:3 to 0:10. Moreover, this process facilitates the formation of perovskite seeds as templates for perovskite crystal growth, effectively reducing the bulk defects in perovskite films. Finally, the obtained PSCs show remarkable power conversion efficiencies (PCEs) of 22.22 and 19.74% for rigid and flexible devices, respectively.

Time‐Resolved Orientation and Phase Analysis of Lead Halide Perovskite Film Annealing Probed by In Situ GIWAXS

AbstractScalable thin‐film deposition methods are increasingly important for hybrid lead halide perovskite thin films. Understanding the structure evolution during non‐equilibrium processes helps to find suitable materials and processing parameters to produce films with well‐performing optoelectronic properties. Here, spin‐cast and slot‐die coated bilayers of lead iodide (PbI2) and methylammonium iodide (MAI) are investigated by in situ grazing‐incidence wide‐angle X‐ray scattering during the thermal annealing process, which converts the bilayer into methylammonium lead iodide (MAPI). Photoluminescence (PL) and UV/Vis measurements show increasing crystallinity during the annealing process and a slight PL red‐shift of the spin‐cast film, attributed to crystallite coalescence that is not prominent for the slot‐die coated film. The disintegration of the solvent‐precursor complex (MA)2(Pb3I8) ⋅ 2 DMSO and conversion into perovskite are followed in situ and differences in the morphology and time evolution are observed. In both, spin‐cast and slot‐die coated thin‐films, the isotropic orientation is dominant, however, in the slot‐die coated films, the perovskite crystallites have an additional face‐on orientation ((110) parallel to substrate) that is not detected in spin‐cast films. An Avrami model is applied for the perovskite crystal growth that indicates reduced dimensionality of the growth for the printed thin films.

Reducing the Trap Density in MAPbI3 Based Perovskite Solar Cells via Bromide Substitution.

The past decade has witnessed tremendous advancement in the field of halide perovskite (PSK) as a choice of material for high-performing solar cells fabrication. Here, we investigate the impact of the halide exchange through N-bromosuccinimide (NBS) treatment in MAPbI3 based solar cells. We observed the partial halide exchange (I- to Br- ) or the filling of halide (X- ) vacancy upon treatment of different NBS concentrations experimentally by spectroscopic and diffractogram studies. We noted that halide exchange impacts the crystallization and is beneficial in improving the photovoltaic performance. The optimized 0.5 % NBS treated PSC exhibited a power conversion efficiency of 17.87 % due to an increment in open-circuit voltage (Voc ) and short circuit current (Jsc ). We noted improved perovskite crystal growth upon Br- substitution; eventually, it helps to lower the trap density, reducing non-radiative recombination and renders the enhancement of long-term stability of PSC.

Combining Perovskites and Quantum Dots: Synthesis, Characterization, and Applications in Solar Cells, LEDs, and Photodetectors

AbstractMetal halide perovskites having high defect tolerance, high absorption characteristics, and high carrier mobility demonstrate great promise as potential light harvesters in photovoltaics and optoelectronics and have experienced an unprecedented development since their occurrence in 2009. Semiconductor quantum dots (QDs), on the other hand, have also been proved to be very flexible toward shape, dimension, bandgap, and optical properties for constructing optoelectronic devices. Of late, a strategic combination of both materials has demonstrated extraordinary promise in photovoltaic applications and optoelectronic devices. Combining QDs and perovskites has proved to be quite an effective strategy toward the formation of pinhole‐free and more stable perovskite crystals along with tunability of other properties. To boost this exciting research field, it is imperative to summarize the work done so far in recent years to provide an intriguing insight. This review is a critical account of the advanced strategy toward combining these two fascinating materials, including their different synthetic approaches regarding heteroepitaxial growth of perovskite crystals on QDs, carrier dynamics at the interface and potential application in the field of solar cells, light emitting diodes, and photodetectors.

Manipulating Crystallization Kinetics in High-Performance Blade-Coated Perovskite Solar Cells via Cosolvent-Assisted Phase Transition.

Manipulating the perovskite solidification process, including nucleation and crystal growth, plays a critical role in controlling film morphology and thus affects the resultant device performance. In this work, a facile and effective ethyl alcohol (EtOH) cosolvent strategy is demonstrated with the incorporation of EtOH into perovskite ink for high-performance room-temperature blade-coated perovskite solar cells (PSCs) and modules. Systematic real-time perovskite crystallization studies uncover the delicate perovskite structural evolutions and phase-transition pathway. Time-resolved X-ray diffraction and density functional theory calculations both demonstrate that EtOH in the mixed-solvent system significantly promotes the formation of an FA-based precursor solvate (FA2 PbBr4 ·DMSO) during the trace-solvent-assisted transition process, which finely regulates the balance between nucleation and crystal growth to guarantee high-quality perovskite films. This strategy efficiently suppresses nonradiative recombination and improves efficiencies in both 1.54 (23.19%) and 1.60eV (22.51%) perovskite systems, which represents one of the highest records for blade-coated PSCs in both small-area devices and minimodules. An excellent VOC deficit as low as 335mV in the 1.54eV perovskite system, coincident with the measured nonradiative recombination loss of only 77mV, is achieved. More importantly, significantly enhanced device stability is another signature of this approach.

Effect of chlorine and bromine on the perovskite crystal growth in mesoscopic heterojunction photovoltaic device

Organic-inorganic hybrid perovskite solar cells are within the emerging photovoltaic technologies. The combination of different halogen ions, in certain fill fractions, is one of the methods to improve the perovskite film properties. Herein, fabrication and characterization of perovskite cells in standard mesoscopic architecture using one-step deposition method has been done. The role of the halogen ions (Chlorine or Bromine) on crystal structure growth and photoelectric performance has been investigated. X-ray diffraction, scanning electron microscopy, atomic force microscopy and optical microscopy analysis were performed. The microstructure, composition and morphology of CH3NH3PbI1.8Br1.2 and CH3NH3PbI1.8Cl1.2 films are dissimilar, although identical fabrication method was used. Same holds for optical properties, band gap energies of 1.84 eV and 1.63 eV, respectively, being obtained. Integrated in solar cells, the maximum power conversion efficiency of the Br based devices is beyond 10%, while for those based on Cl, the efficiency drops around 5%.

Chemical Polishing of Perovskite Surface Enhances Photovoltaic Performances.

The benefits of excess PbI2 on perovskite crystal nucleation and growth are countered by the photoinstability of interfacial PbI2 in perovskite solar cells (PSCs). Here we report a simple chemical polishing strategy to rip PbI2 crystals off the perovskite surface to decouple these two opposing effects. The chemical polishing results in a favorable perovskite surface exhibiting enhanced luminescence, prolonged carrier lifetimes, suppressed ion migration, and better energy level alignment. These desired benefits translate into increased photovoltages and fill factors, leading to high-performance mesostructured formamidinium lead iodide-based PSCs with a champion efficiency of 24.50%. As the interfacial ion migration paths and photodegradation triggers, dominated by PbI2 crystals, were eliminated, the hysteresis of the PSCs was suppressed and the device stability under illumination or humidity stress was significantly improved. Moreover, this new surface polishing strategy can be universally applicable to other typical perovskite compositions.

Preparation and performance of perovskite solar cells with two dimensional MXene as active layer additive

In this paper, two-dimensional titanium carbide (Ti3C2Tx) and vanadium carbide (V2CTx) MXene with appropriate mass content are incorporated into PbI2 precursor solution to fabricate perovskite film via one-step coating method. The effects of the addition of MXene with different mass ratio on the morphology, crystallinity, light absorption property and stability of the CH3NH3PbI3 film and the photovoltaic performance and stability of the corresponding devices are further investigated. The results demonstrate that the introduction of Ti3C2Tx and V2CTx additive can improve the morphology of perovskite film, increase the grain size of perovskite film, enhance the hydrophobicity of the perovskite layer. As a result, improved photovoltaic performance can be achieved. By modifying the proportion of additives, the power conversion efficiency (PCE) of V2CTx MXene modified solar cells is better than those of the devices with Ti3C2Tx additive and the pristine one. Compared with the control device without additive, perovskite solar cells incorporating V2CTx additive with an optimized concentration of 0.0013 wt% achieve a PCE of 17.61% (increased by 17%). Moreover, for perovskite film incorporating V2CTx additive, unique morphology with uniform grain size and ordered layered crystal particle can be noted. This means the V2CTx additive can regulate the perovskite crystal film growth. In addition, the V2CTx additive incorporated devices can retain 68.29% of the initial PCE after 15 days, which is higher than the devices without additives (by 9.69%) and with Ti3C2Tx as additive (by 47.16%), owing to the better crystallinity and higher quality of perovskite film. Our work provides an effective method for improving performance of perovskite solar cells and expands the applications areas of V2CTx in photovoltaics.

Boost the efficiency of nickel oxide-based formamidinium-cesium perovskite solar cells to 21% by using coumarin 343 dye as defect passivator

Inverted perovskite solar cells (PSCs) based on formamidinium-cesium (FACs) perovskites with nickel oxide as hole transport layer (HTL) have attracted much attention due to their good stability. However, their open-circuit voltage (VOC) and efficiencies lag far behind those of inverted PSCs based on organic HTLs. Here, we introduce an organic dye coumarin 343 (C343) as a molecular additive into the perovskite to reduce VOC loss and improve the efficiency of nickel oxide-based inverted PSCs. We demonstrate that the strong coordination between the carboxyl groups in C343 and under-coordinated Pb2+ not only optimizes perovskite crystal growth during perovskite formation, but also reduces the defects densities within perovskite films. As a result, our C343 doped PSCs achieve an optimal efficiency of 20.9% (certified 20.2%), which is one of the highest efficiencies for FACs perovskite and nickel oxide based inverted PSCs reported so far. Moreover, the utilization of C343 also benefits devices’ stability, making the devices maintain over 94% and 95% of the initial PCE after aging at 85 °C for 500 h in N2 glovebox and operation under continuous 1 sun illumination with the maximum power point (MPP) tracking at the temperature around 65 °C in ambient air for 500 h, respectively.

Unveiling the effect of amino acids on the crystallization pathways of methylammonium lead iodide perovskites

Multifunctional additives are widely used to improve crystallization and to passivate defects in perovskite solar cells. The roles of these additives are usually related to the various functional groups contained in such additives. Here, we introduce a serious of analogues of amino acids into methylammonium lead iodide perovskites and find they play different roles in the crystallization process despite the fact that these additives share exactly the same terminal groups, namely one amino group and one carboxyl group. The corresponding crystallization pathways are established for the first time via monitoring the time-resolved phase formation and transformation. We find that avoiding the rapid formation of perovskites from precursor solution can facilitate the uniform nucleation and growth of perovskite crystals with enhanced crystallinity and reduced defects. Further, we find the different crystallization behaviors probably arise from the inherent structural characteristic of these additives, leading to different interactions in the precursors. This study unveils the effects of amino acids on the liquid–solid crystallization process and helps better understand the role of multifunctional additives beyond their functional groups.

Photo-enhanced growth of lead halide perovskite crystals and their electro-optical properties.

Organic-inorganic hybrid perovskites have attracted much attention for opto-electronic applications due to their low trap density, strong light absorption, and superior charge transport performance. Generally, the high efficiency of perovskite electro-optical thin films depends on their high-quality perovskite single crystals. In this work, the external illumination is applied on the perovskite single crystals growing in solution. It was shown that larger size CH3NH3PbI3 single crystals can be obtained under illumination conditions. In addition, CH3NH3PbI3 films are prepared by a one-step spin coating process under illumination, the crystal size and film quality of which have been obviously improved due to the effect of illumination in the film forming process. The efficiency of the average cells based on CH3NH3PbI3 films increased from 15.2% for the normal conditions to 17.7% for the illumination one, which is consistent with the light enhanced growth of CH3NH3PbI3 single crystals in their solution. The "photo-inhibition nucleation" mechanism is proposed to explain the light-induced enhancement of perovskite crystal growth.

Controllable metastable growth of perovskite single crystals for highly sensitive X-ray detection

MAPbBr3 single crystals (SCs) were obtained by a low-temperature controllable metastable crystallization method, which regulates the growth process to low temperature and ensures excellent optoelectronic properties of the as-prepared SCs.

Anisotropy Growth of Perovskite Crystal Induced by Layered Double Hydroxide for Efficiency Enhancement of Solar Cell

Anisotropy Growth of Perovskite Crystal Induced by Layered Double Hydroxide for Efficiency Enhancement of Solar Cell

Size-tunable MoS2nanosheets for controlling the crystal morphology and residual stress in sequentially deposited perovskite solar cells with over 22.5% efficiency

MoS2nano-scaffolds are introduced into the PbI2skeleton during a sequential deposition process to realize the homogeneous growth of perovskite crystals through expanding the physical volume of the PbI2layer and reducing film residual stress.

Resonance-Mediated Dynamic Modulation of Perovskite Crystallization for Efficient and Stable Solar Cells.

Manipulating perovskite crystallization to prepare high-quality perovskite films is the key to achieving highly efficient and stable perovskite solar cells (PSCs). Here, a dynamic strategy is proposed to modulate perovskite crystallization using a resonance hole-transporting material (HTM) capable of fast self-adaptive tautomerization between multiple electronic states with neutral and charged resonance forms for mediating perovskite crystal growth and defect passivation in situ. This approach, based on resonance variation with self-adaptive molecular interactions between the HTM and the perovskite, produces high-quality perovskite films with smooth surface, oriented crystallization, and low charge recombination, leading to high-performance inverted PSCs with power conversion efficiencies approaching 22% for small-area devices (0.09cm2 ) and up to 19.5% for large-area devices (1.02cm2 ). Also, remarkably high stability of the PSCs is observed, retaining over 90%, 88%, or 83% of the initial efficiencies in air with relative humidity of 40-50%, under continuous one-sun illumination, or at 75°Cannealing for 1000 h without encapsulation.

Influence of molar ratio of MAI and PbI2 on synthesis of perovskite film

This study explores the influence of molar ratio of the synthetic solution of methylammonium iodide (MAI) and PbI2 on perovskite solar cells. The complete perovskite crystals must be produced in a low-humidity environment. The substrate is spin-coated in the adjusted MAPbI3 synthesis solution and annealed by using a nitrogen furnace tube to form perovskite crystals. During the crystallization of MAPbI3, some of the PbI2 remains, which improves the efficiency of the perovskite solar cell. Therefore, we adjust the molar concentration of MAI to find the appropriate amount of the PbI2 residual. We fix the MAI molar concentration at 1 M and adjust the PbI2 molar concentration from 0.8 M to 1.4 M. The molar ratios of MAI and PbI2 are, then, 1:0.8, 1:1, 1:1.2, and 1:1.4, respectively. Then, we use UV–vis, FE-SEM, and photoelectric conversion efficiency (PCE) measurements for comparing the growth of perovskite crystals and their photoelectric characteristics. The results show that 1.2 M of PbI2 is the most appropriate concentration for perovskite solar cells among the adjusted concentrations.

Interface Chelation Induced by Pyridine‐Based Polymer for Efficient and Durable Air‐Processed Perovskite Solar Cells

AbstractPolymer doping is a significant approach to precisely control nucleation and crystal growth of perovskites and enhance electronic quality in perovskite solar cells (PSC) prepared in air. Here, a brand‐new self‐healing polysiloxane (SHP) with dynamic 2,6‐pyridinedicarboxamide (PDCA) coordination units and plenty of hydrogen bonds was designed and incorporated into perovskite films. PDCA units, showing strong intermolecular Pb2+‐Namido, I−‐Npyridyl, and Pb2+‐Oamidocoordination interactions, were expected to enhance crystallinity and passivate the grain boundary. In addition, abundant hydrogen bonds in SHP afforded the self‐healing of cracks at grain boundaries for fatigue PSCs. Significantly, the doped device demonstrated a champion efficiency of 19.50 % with inconspicuous hysteresis, almost rivaling those achieved in control atmosphere. This strategy of heterocyclic‐based macromolecular doping in PSCs will pave a way for realizing efficient and durable crystalline semiconductors.

Interface Chelation Induced by Pyridine-Based Polymer for Efficient and Durable Air-Processed Perovskite Solar Cells.

Polymer doping is a significant approach to precisely control nucleation and crystal growth of perovskites and enhance electronic quality in perovskite solar cells (PSC) prepared in air. Here, a brand-new self-healing polysiloxane (SHP) with dynamic 2,6-pyridinedicarboxamide (PDCA) coordination units and plenty of hydrogen bonds was designed and incorporated into perovskite films. PDCA units, showing strong intermolecular Pb2+ -Namido , I- -Npyridyl , and Pb2+ -Oamido coordination interactions, were expected to enhance crystallinity and passivate the grain boundary. In addition, abundant hydrogen bonds in SHP afforded the self-healing of cracks at grain boundaries for fatigue PSCs. Significantly, the doped device demonstrated a champion efficiency of 19.50 % with inconspicuous hysteresis, almost rivaling those achieved in control atmosphere. This strategy of heterocyclic-based macromolecular doping in PSCs will pave a way for realizing efficient and durable crystalline semiconductors.