Organic Halide Salts Research Articles

Enhancing efficiency through surface passivation of carbon-based perovskite solar cells

Perovskite solar cells (PSCs) have made significant strides in power conversion efficiency (PCE), but their commercialization remains limited by stability issues. Additionally, the high cost of electrodes like gold necessitates the exploration of more affordable alternatives such as carbon (graphene). In this study, we present an approach that combines material dimensionality control and interfacial passivation using post-device treatment with phenethylammonium iodide (PEAI), an organic halide salt, to enhance the efficiency of carbon-based PSCs. Effective defect passivation is key to further improving the PCE and open-circuit voltage (VOC) of PSCs. Our results show that PEAI successfully passivates defects on the perovskite surface, significantly reducing non-radiative recombination. As a result, we achieved carbon-based PSCs with an impressive efficiency of 19.3%, demonstrating excellent stability under maximum power point tracking (MPPT) for over 900 h.

Dual modification engineering enabled efficient perovskite solar cells with high open-voltage of 1.233 V

Interface engineering take as a crucial role in enhancing the performance of perovskite solar cells (PSCs). Here, we propose a comprehensive strategy to improve the performance and stability of PSCs through dual-interface modification approach. This strategy involves simultaneously introducing lead-free Cs3MnBr5: Ce3+ nanocrystals (NCs) between SnO2 electron transport layer and the perovskite layer, as well as 1H,1H-Perfluorooctylamine iodide (PFOAI) at the interface between perovskite and Spiro-OMeTAD hole transport layer. Firstly, we successfully prepare Cs3MnBr5: Ce3+ NCs, which exhibits an extensive ultraviolet response and effective blue photoluminescence. The photoluminescence quantum yield of Cs3MnBr5: Ce3+ NCs can reach 90 %, demonstrating efficient photon down-conversion ability and efficient defect passivation. Simultaneously, the organic halide salt PFOAI with super-hydrophobic properties efficiently passivates defects on the surface of perovskite and improves moisture-resistance of perovskite films. Taking advantage of these synergistic effects, we achieve efficient PSCs based the Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3 and Cs0.05(FA0.95MA0.05)0.95Pb(I0.95Br0.05)3 with power conversion efficiency (PCE) of 23.88 % and 24.24 %. We also achieved an ultrahigh open-circuit voltage (VOC) of 1.233 V, which represents one of the highest VOC values in a perovskite film with a bandgap of ∼1.60 eV. Additionally, the non-encapsulated double-interface modified PSCs exhibit long time, light and humidity stability. This study explores a novel and comprehensive strategy for manufacturing PSCs with high VOC, high PCE, and good stability.

Synergetic Effect of Aluminum Oxide and Organic Halide Salts on Two‐Dimensional Perovskite Layer Formation and Stability Enhancement of Perovskite Solar Cells (Adv. Energy Mater. 39/2023)

Synergetic Effect of Aluminum Oxide and Organic Halide Salts on Two‐Dimensional Perovskite Layer Formation and Stability Enhancement of Perovskite Solar Cells (Adv. Energy Mater. 39/2023)

Organic halide salts and PbI2 in improving the efficiency of perovskite solar cells

First developed in 2012, perovskite solar cells (PSC) have been attracting enormous attention for their high-power conversion efficiency, low manufacturing cost, easy annealing and fabricating techniques, good stability in ambient environments, and excellent overall performance. Skyrocketing from a PCE of 2.8% to 25.2%, PSCs are deemed as one of the most promising solar energy harvesters in the near future. However, due to the grain boundaries and some poor interface connections, there appear several defects that affect the efficiency and stability of PSCs. In this case, two primary methods are discussed in this review to minimize such limitations: the introduction of (1) PbI2 and (2) organic halide salts as additives to the perovskite film. By filling the vacancies at the grain boundary, promoting spatial electron–hole separation, generating Lewis acid–base reaction, and forming intermolecular interactions like hydrogen bonding, sulfide bonds, pi-conjunctions, etc., these additives serve as promising candidates for reducing the surface recombination of PSCs. Moreover, because of the hydrophobic characteristics of organic halide-based compounds and the thermal annealing process, the stability of PSCs can also be improved in both high-temperature and -humidity environments. Through presenting and compiling the results of recent studies on various additives, this review also proposes further development and next-generation strategies for minimizing the limitations and challenges in the future.

Synergetic Effect of Aluminum Oxide and Organic Halide Salts on Two‐Dimensional Perovskite Layer Formation and Stability Enhancement of Perovskite Solar Cells

AbstractLong‐chain organic halide salts are widely used in perovskite‐based optoelectronic devices for surface passivation owing to their capability to interact with the surface defects of perovskites. Here, aluminum oxide (AlOx) is introduced via atomic layer deposition onto octylammonium iodide (OAI) to exploit the benefits of organic halide salts without generating undesired defects. The devices incorporating AlOx on OAI‐treated perovskite (OAI/AlOx) show enhancement in both device performance and photo‐stability compared to those with only treatment. A diffusion of aluminum from AlOx into the perovskite through surface characterization contributes to a uniform photo‐generated carrier transport in both the surface and the bulk of the perovskite absorber. In addition, it is revealed that light‐induced two‐dimensional perovskite formation on OAI/AlOx. This may be ascribed to preventing the loss of OA cations due to the presence of AlOx, leading to a decrease in the number of iodine anions which suppresses the light‐induced degradation of corresponding devices. Consequently, the devices show over 24% efficiency and retain their efficiency over 1000 hours under continuous light illumination.

2,2,2-Trifluoroethanol-Assisted Construction of 2D/3D Perovskite Heterostructures for Efficient and Stable Perovskite Solar Cells Made in Ambient Air.

To achieve future commercialization of perovskite solar cells (PSCs), balancing the efficiency, stability, and manufacturing cost is required. In this study, we develop an air processing strategy for efficient and stable PSCs based on 2D/3D heterostructures. The organic halide salt phenethylammonium iodide is adopted to in situ construct a 2D/3D perovskite heterostructure, in which 2,2,2-trifluoroethanol as a precursor solvent is introduced to recrystallize 3D perovskite and form an intermixed 2D/3D perovskite phase. This strategy simultaneously passivates defects, reduces nonradiative recombination, prevents carrier quenching, and improves carrier transport. As a result, a champion power conversion efficiency of 20.86% is obtained for air-processed PSCs based on 2D/3D heterostructures. Moreover, the optimized devices exhibit superior stability, remaining more than 91 and 88% of their initial efficiencies after 1800 h of storage under dark condition and 24 h of continuous heating at 100 °C, respectively. Our study provides a convenient method to fabricate all-air-processed PSCs with high efficiency and stability.

Synergistic strategy of rubidium chloride regulated SnO2 and 4-tert-butyl-benzylammonium iodide passivated MAxFA1-xPbI3 for efficient mixed-cation perovskite solar cells

Nowadays, the MA-FA mixed-cation perovskite solar cells (PSCs), demonstrating much higher stability than that of single-cation MAPbI3 or FAPbI3, are still encountering a low-efficiency issue. The main reason is that there existing a lot of defects in SnO2 electron transport layers (ETLs) and perovskite absorbers. Herein, we develop a synergistic strategy of Rubidium Chloride (RbCl) doping and 4-tert-butylbenzylammonium iodide (tBBAI) passivation to fabricate high-performance MAxFA1-xPbI3 mixed-cation PSCs. The alkali halide RbCl is first selected as a novel doping additive to regulate the film properties of SnO2 and perovskites. Research shows that the negative Cl- ions can combine with uncoordinated Sn4+ ions due to their strong bonding ability, which can passivate the oxygen-vacancy-related defects and enhance the charge transport of SnO2 ETLs. Meanwhile, the doped Rb+ and Cl- ions may diffuse into perovskite lattices to promote grain growth and reduce the defects of perovskites. Besides, we employ an organic halide salt tBBAI to passivate perovskites and suppress surface defects. Results of deep level transient spectroscopy (DLTS) indicate that SnO2 and SnO2-RbCl based devices have deeper hole traps and large trap densities (ΔE = 0.92 eV, NT = 1.10 × 1016 cm−3; ΔE = 0.93 eV, NT = 2.16 × 1015 cm−3); while tBBAI-treated SnO2-RbCl-based devices own a shallower hole trap and a smaller trap density (ΔE = 0.72 eV, NT = 2.44 × 1013 cm−3); and the corresponding IPb and I(MA/FA) antisite defeats are also identified. Therefore, our synergistic strategy is effectively able to reduce the defect density and suppress the non-radiative recombination. Consequently, the best-performance MA0.85FA0.15PbI3 PSCs achieve an impressive power conversion efficiency (PCE) of 22.54% with a large open circuit voltage (Voc) of 1.16 V, which are by far the highest values of MA0.85FA0.15PbI3 mixed-cation PSCs.

Multi‐Site Intermolecular Interaction for In Situ Formation of Vertically Orientated 2D Passivation Layer in Highly Efficient Perovskite Solar Cells

AbstractSurface passivation via 2D perovskite is critical for perovskite solar cells (PSCs) to achieve remarkable performances, in which the applied spacer cations play an important role on structural templating. However, the random orientation of 2D perovskite always hinder the carrier transport. Herein, multiple nitrogen sites containing organic spacer molecule (1H‐Pyrazole‐1‐carboxamidine hydrochloride, PAH) is introduced to form 2D passivation layer on the surface of formamidinium based (FAPbI3) perovskite. Deriving from the interactions between PAH and PbI2, the defects of FAPbI3 perovskite are effectively passivated. Interestingly, due to the multiple‐site interactions, the 2D nanosheets are found to grow perpendicularly to the substrate for promotion of charge transfer. Therefore, an impressive power conversion efficiency of 24.6% and outstanding long‐term stability are achieved for the 2D/3D perovskite devices. The findings further provide a perspective in structure design of novel organic halide salts for the fabrication of efficient and stable PSCs.

Regioselective Multisite Atomic-Chlorine Passivation Enables Efficient and Stable Perovskite Solar Cells.

Passivating defects using organic halide salts, especially chlorides, is an effective method to improve power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) arising from the stronger Pb-Cl bonding than Pb-I and Pb-Br bonding. However, Cl- anions with a small radius are prone to incorporation into the perovskite lattice that distorts the lead halide octahedron, degrading the photovoltaic performance. Here, we substitute atomic-Cl-containing organic molecules for widely used ionic-Cl salts, which not only retain the efficient passivation by Cl but also prevent the incorporation of Cl into the bulk lattice, benefiting from the strong covalent bonding between Cl atoms and organic frameworks. We find that only when the distance of Cl atoms in single molecules matches well with the distance of halide ions in perovskites can such a configuration maximize the defect passivation. We thereby optimize the molecular configuration to enable multiple Cl atoms in an optimal spatial position to maximize their binding with surface defects. The resulting PSCs achieve a certified PCE of 25.02%, among the highest PCEs for PSCs, and retain 90% of their initial PCE after 500 h of continuous operation.

Elucidation of the Alternating Copolymerization Mechanism of Epoxides or Aziridines with Cyclic Anhydrides in the Presence of Halide Salts.

Organic halide salts in combination with metal or organic compound are the most common and essential catalysts in ring-opening copolymerizations (ROCOP). However, the role of organic halide salts was neglected. Here, we have uncovered the complex behavior of organic halides in ROCOP of epoxides or aziridine with cyclic anhydride. Coordination of the chain-ends to cations, electron-withdrawing effect, leaving ability of halide atoms, chain-end basicity/nucleophilicity, and terminal steric hindrance cause three types of side reactions: single-site transesterification, substitution, and elimination. Understanding the complex functions of organic halide salts in ROCOP led us to develop highly active and selective aminocyclopropenium chlorides as catalysts/initiators. Adjustable H-bonding interactions of aminocyclopropenium with propagating anions and epoxides create chain-end coordination process that generate highly reactive carboxylate and highly selective alkoxide chain-ends.

Elucidation of the Alternating Copolymerization Mechanism of Epoxides or Aziridines with Cyclic Anhydrides in the Presence of Halide Salts

AbstractOrganic halide salts in combination with metal or organic compound are the most common and essential catalysts in ring‐opening copolymerizations (ROCOP). However, the role of organic halide salts was neglected. Here, we have uncovered the complex behavior of organic halides in ROCOP of epoxides or aziridine with cyclic anhydride. Coordination of the chain‐ends to cations, electron‐withdrawing effect, leaving ability of halide atoms, chain‐end basicity/nucleophilicity, and terminal steric hindrance cause three types of side reactions: single‐site transesterification, substitution, and elimination. Understanding the complex functions of organic halide salts in ROCOP led us to develop highly active and selective aminocyclopropenium chlorides as catalysts/initiators. Adjustable H‐bonding interactions of aminocyclopropenium with propagating anions and epoxides create chain‐end coordination process that generate highly reactive carboxylate and highly selective alkoxide chain‐ends.

Application of lamellar nickel hydroxide membrane as a tunable platform for ionic thermoelectric studies.

The recent trend in thermoelectric literature suggests that ionic thermoelectric (i-TE) materials are ideal for directly converting low-grade waste heat into electricity. Here, we developed a unique platform for i-TE studies by stacking two-dimensional sheets of β-Ni(OH)2 prepared by a bottom-up method. The lamellar membrane of β-Ni(OH)2 (Ni-M) itself does not display significant thermovoltages, but when doped with mobile anion-generating species (like aminopropyl functionalized magnesium phyllosilicate or organic halide salts), it exhibits significant negative Seebeck coefficient (up to -13.7 ± 0.2 mV K-1). Similarly, upon doping with cation-generating species like poly(4-styrene sulfonic acid) (PSS), it displays positive Seebeck coefficient values (up to +12 ± 1.9 mV K-1). The positive and negative i-TE materials prepared by doping Ni-M are assembled into ionic thermopiles capable of generating thermovoltages up to 1 V, at ΔT = 12 K. The Ni-M-based nanofluidic systems demonstrated an additional path of electricity harvesting by connecting colder zones of the positive and negative i-TE materials with other ion conducting membranes. In contrast to organic polymer-based i-TE systems, the Ni-M based system exhibited consistent performance despite being exposed to high temperatures (∼200 °C, 5 minutes).

Synergetic Passivation of Metal‐Halide Perovskite with Fluorinated Phenmethylammonium toward Efficient Solar Cells and Modules

AbstractSurface passivation with organic halide salts is a powerful strategy to enhance the performance of perovskite solar cells. However, the inevitable formed in‐plane favored two‐dimensional perovskite layers with low carrier mobility and high binding energy inhibit the interfacial charge transfer within the device. Herein, a bulky fluorinated phenmethylammonium salt is designed and synthesized to passivate the perovskite film without forming 2D perovskites. A strong interaction which is induced by an electron donation from passivation agent to perovskite not only reduces the defects at the top surface of the perovskite, but also suppresses the recombination reaction at the buried surface due to a permeation of the organic halide salt. Moreover, the results of time resolved photoluminescence and confocal microscopy images suggest that the interfacial charge transfer speed and uniformity are enhanced. As a result, the efficiency of a small‐area device increases from 20.7 ± 0.9% to 22.8 ± 0.4% (aperture: 0.16 cm2). Moreover, a stabilized efficiency of 18.0% (aperture: 10.0 cm2) is achieved for larger‐area modules with 6‐series connected sub‐cells. Equally important, the non‐encapsulated modules show significantly improved stability at ambient conditions (ISOS‐D‐1). These significant improvements provided by a simple and reproducible procedure can be readily adopted in other types of devices.

Organic ligand complementary passivation to Colloidal-quantum-dot surface enables efficient infrared solar cells

Lead sulfide colloidal quantum dot (PbS CQD) solar cells present great potential in infrared (IR) conversion due to high IR absorption coefficient and solution processability. The large-size IR QDs introduce specific nonpolar (100) facets that undisplay in small-size CQDs. The neutrality of (100) facets and reversible ligand exchange process are crucial challenges for IR QD surface passivation. Here, organic halide salt phenethylammonium iodide/bromine (PEAX, X = I/Br) additive ligands are adopted to cooperate with traditional lead halides for QD surface passivation especially for (100) neutral facets. Both nuclear magnetic resonance (NMR) and density functional theory (DFT) simulation reveal that the organic ligand PEAX can bind on PbS QD planes to enhance passivation without compromising transport property. Further device related photophysical studies confirm the suppressed bulk and interface defect concentration. The optimal PEABr based solar cells possess a power conversion efficiency (PCE) of 12.28 % under solar AM1.5G (certified value of 11.98 %). The crystalline Si filtered efficiency reaches 1.42 %. Both efficiencies are the record values for such absorption range QD (excitonic peak ∼1.3 μm) solar cells. Moreover, the supplementary PEAX ligand suppress the migration of halogen ions and elevate device stability.

In Situ Halide Exchange of Cesium Lead Halide Perovskites for Blue Light-Emitting Diodes.

3D perovskites are promising to achieve efficient and bright deep-blue light-emitting diodes (LEDs), which are required for lighting and display applications. However, the efficiency of deep-blue 3D perovskite-based LEDs is limited by high density of defects in perovskites, and their deep-blue emission is not easy to achieve due to the halide phase separation and low solubility of chloride in precursor solutions. Here, an in situ halide exchange method is developed to achieve deep-blue 3D perovskites by spin-coating an organic halide salts solution to treat blue 3D perovskites. It is revealed that the halide-exchange process is mainly determined by halide ion diffusion targeting a concentration equalization, which leads to homogeneous 3D mixed-halide perovskites. By further introducing multifunctional organic ammonium halide salts into the exchange solution to passivate defects, high-quality deep-blue perovskites with reduced trap density can be obtained. This approach leads to efficient deep-blue perovskite LEDs with a peak external quantum efficiency (EQE) of 4.6% and a luminance of 1680cdm-2 , which show color coordinates of (0.131, 0.055), very close to the Rec. 2020 blue standard. Moreover, the halide exchange method is bidirectional, and blue perovskite LEDs can be achieved with color coordinates of (0.095, 0.160), exhibiting a high EQE of 11.3%.

Highly thermally stable multi-porous calcium aluminum hydrotalcite catalyst for efficient carbonate synthesis

In the context of a carbon–neutral era, conversion of greenhouse gas CO2via chemical catalysis is a powerful means. Using CO2and petroleum-derived alkylene oxide as the raw materials to produce high-value carbonate substances has been considered a green and economic path for carbon reduction and energy transition. We discovered a multi-porous calcium aluminum hydrotalcite material (Ca-Al HT), and found that it performs excellent catalytic ability on transesterification (an important reaction in the synthesis of carbonates). Being different from homogeneous basic catalysts such as soluble metal hydroxides and organic halide salts, and well-known solid basic catalyst CaO, which are difficult to recycle and suffer severe deactivation in long-term catalytic process, the robust Ca12Al14O33crystal phase in Ca-Al HT catalyst behaves much more stable catalytic performance during 4000 min efficient catalysis (63 % conversion and 100 % selectivity). The special crystal phase structure of Ca12Al14O33remains stable at even a very high temperature of 900 °C. In contrast, CaO as the reference catalyst is very sensitive to trace H2O in catalytic system, and deactivates immediately. The outstanding catalytic ability of Ca-Al HT is attributed to its super-strong alkali strength, large alkali amount, and quick mass transfer originating from the hierarchical pore system.

Highly thermally stable multi-porous calcium aluminum hydrotalcite catalyst for efficient carbonate synthesis

<h2>Abstract</h2> In the context of a carbon-neutral era, conversion of greenhouse gas CO₂ via chemical catalysis is a powerful means. Using CO₂ and petroleum-derived alkylene oxide as the raw materials to produce high-value carbonate substances has been considered a green and economic path for carbon reduction and energy transition. We discovered a multi-porous calcium aluminum hydrotalcite material (Ca-Al HT), and found that it performs excellent catalytic ability on transesterification (an important reaction in the synthesis of carbonates). Being different from homogeneous basic catalysts such as soluble metal hydroxides and organic halide salts, and well-known solid basic catalyst CaO, which are difficult to recycle and suffer severe deactivation in long-term catalytic process, the robust Ca₁₂Al₁₄O₃₃ crystal phase in Ca-Al HT catalyst behaves much more stable catalytic performance during 4000 min efficient catalysis (63% conversion and 100% selectivity). The special crystal phase structure of Ca₁₂Al₁₄O₃₃ maintains stability at even a very high temperature of 900 °C. In contrast, CaO as the reference catalyst is very sensitive to trace H₂O in catalytic system, and deactivates immediately. The outstanding catalytic ability of Ca-Al HT is attributed to its super-strong alkali strength, large alkali amount, and quick mass transfer originating from the hierarchical pore system.

Hysteresis‐Free Planar Perovskite Solar Module with 19.1% Efficiency by Interfacial Defects Passivation

In few years, perovskite solar devices have reached high efficiency on lab scale cells. Upscaling to module size, effective perovskite recipe and posttreatment are of paramount importance to the breakthrough of the technology. Herein this work, the development of a low‐temperature planar n–i–p perovskite module (11 cm2 aperture area, 91% geometrical fill factor) is reported on, exploiting the defect passivation strategy to achieve an efficiency of 19.1% (2% losses stabilized) with near‐zero hysteresis, that is the most unsolved issue in the perovskite photovoltaic technology. The I/Br (iodine/bromide) halide ion ratio of the triple‐cation perovskite formulation and deposition procedure are optimized to move from small area to module device and to avoid the detrimental effect of dimethyl sulfoxide (DMSO) solvent. The organic halide salt phenethylammonium iodide (PEAI) is adopted as surface passivation material on module size to suppress perovskite defects. Finally, homogeneous and defect‐free layers from cell to module with only 8% relative efficiency losses, high reproducibility, and optimized interconnections are scaled by laser ablation methods. The homogeneity of the perovskite layers and of the full stack was assessed by optical, morphological, and light beam–induced current (LBIC) mapping characterizations.

2D/3D Heterojunction perovskite light-emitting diodes with tunable ultrapure blue emissions

High performance blue light-emitting diodes are indispensable for solid-state lighting and full-color displays. Recently, tremendous efforts have been dedicated to boost the performance for blue perovskite light-emitting diodes (PeLEDs). In this work, we construct an ingenious 2D/3D heterostructure perovskite by long-chain organic halide salt post-treatment in blue perovskites for the first time. Organic halide salt post-treatment can form a 2D capping layer on the original 3D perovskite surface, thus to passivate defects and improve exciton radiative recombination rate. As a result, 2D/3D PeLEDs with tunable blue emissions (465, 475, and 486 nm), ultra-low turn-on voltages (3.0, 2.7, and 2.7 V), high brightness (928, 6727, and 9242 cd m−2), and excellent EQEs (2.11%, 6.29%, and 8.57%) are demonstrated. Moreover, due to the high phase homogeneity, the optimized PeLEDs exhibit ultrapure blue emissions (FWHM < 15 nm), in which the PeLED (465 nm) achieve ≈ 98% coverage of the Rec. 2020 standard.

Surface Passivation of MAPbBr3 Perovskite Single Crystals to Suppress Ion Migration and Enhance Photoelectronic Performance.

Recently, organometal halide perovskites (OHPs) have achieved significant advancement in photovoltaics, light-emitting diodes, X-ray detectors, and transistors. However, commercialization and practical applications were hindered by the notorious ion migration issue of OHPs. Here, we report a simple solvent-based surface passivation strategy with organic halide salts (methylammonium bromide (MABr) and phenylethylammonium bromide (PEABr)) to suppress the ion migration of MAPbBr3 single crystals. The surface passivation effect is evidenced by the stronger photoluminescence (PL) intensity and extended PL lifetime. Using the pulse voltage and continuous voltage current-voltage measurements, we found that single crystals with surface passivation showed negligible hysteresis on the surface due to the suppression of ion migration. As a result, the dark current stability of coplanar structure devices was significantly improved. Moreover, the vertical structure X-ray detectors with PEABr treatment exhibited a high sensitivity of 15 280 μC Gyair-1 cm-2 and a low detection limit of 87 nGyair s-1 under 5 V bias. The proposed technology would be a versatile tool to improve the performance of perovskite photoelectronic devices.