Spacer Cations Research Articles

Highly Efficient and Stable FA-Based Quasi-2D Ruddlesden-Popper Perovskite Solar Cells by the Incorporation of β-Fluorophenylethanamine Cations.

2D Ruddlesden-Popper (2D RP) perovskite, with attractive environmental and structural stability, has shown great application in perovskite solar cells (PSCs). However, the relatively inferior photovoltaic efficiencies of 2D PSCs limit their further application. To address this issue, β-​fluorophenylethanamine (β-​FPEA) as a novel spacer cation is designed and employed to develop stable and efficient quasi-2D RP PSCs. The strong dipole moment of the β-​FPEA enhancesthe interactions between the cations and [PbI6 ]4- octahedra, thus improving the charge dissociation of quasi-2D RP perovskite. Additionally, the introduction of the β-​FPEA cation optimizesthe energy level alignment, improvesthe crystallinity, stabilizesboth the mixed phase and a-FAPbI3 phase of the quasi-2D RP perovskite film, prolongsthe carrier diffusion length, increasesthe carrier lifetime and decreasesthe trap density. By incorporating the β-​FPEA, the quasi-2D RP PSCs exhibita power conversion efficiency (PCE) of 16.77% (vs phenylethylammonium (PEA)-based quasi-2D RP PSCs of 12.81%) on PEDOT:PSS substrate and achievea champion PCE of 19.11% on the PTAA substrate. It is worth noting that the unencapsulated β-​FPEA-based quasi-2D RP PSCs exhibitconsiderably improved thermal and moisture stability. These findings provide an effective strategy for developing novel spacer cations for high-performance 2D RP PSCs.

Rational Regulation of Organic Spacer Cations for Quasi‐2D Perovskite Solar Cells

Quasi‐two‐dimensional perovskite solar cells (quasi‐2D PSCs) have drawn significant attention and are rapidly developing owing to the impressive stability of the materials and devices. However, there are no reliable guidelines for designing and selecting suitable organic spacer cations to achieve high power conversion efficiency (PCE) in quasi‐2D PSCs. Herein, the effects of the spacer cations with different substituents, i.e., benzylamine (PMA), 4‐methoxybenzylamine (p‐MeOPMA), and 4‐fluorobenzylamine (p‐FPMA), on the optoelectronic properties and device performance of quasi‐2D perovskites are systematically investigated. It is found that the spacer cations with different substituents mainly affect the crystal growth and film quality of quasi‐2D perovskites. Interestingly, quasi‐2D perovskites based on p‐MeOPMA or p‐FPMA exhibit poor crystallinity and crystal orientation, while quasi‐2D perovskite based on the unsubstituted PMA shows improved crystallinity and crystal orientation, which enables suppressed trap densities and efficient charge transport. The PMA‐based quasi‐2D perovskite (nominal n = 3) solar cell exhibits the highest PCE of 13.58%. These results demonstrate that the rational regulation of organic spacer cations plays a crucial role in improving the crystallinity and crystal orientation of perovskite films and elucidate key guiding rules for organic spacer cations for high‐performance quasi‐2D PSCs.

Modification of Two-Dimensional Tin-Based Perovskites by Pentanoic Acid for Improved Performance of Field-Effect Transistors.

Understanding and controlling the nucleation and crystallization in solution-processed perovskite thin films are critical to achieving high in-plane charge carrier transport in field-effect transistors (FETs). This work demonstrates a simple and effective additive engineering strategy using pentanoic acid (PA). Here, PA is introduced to both modulate the crystallization process and improve the charge carrier transport in 2D 2-thiopheneethylammonium tin iodide ((TEA)2 SnI4 ) perovskite FETs. It is revealed that the carboxylic group of PA is strongly coordinated to the spacer cation TEAI and [SnI6 ]4- framework in the perovskite precursor solution, inducing heterogeneous nucleation and lowering undesired oxidation of Sn2+ during the film formation. These factors contribute to a reduced defect density and improved film morphology, including lower surface roughness and larger grain size, resulting in overall enhanced transistor performance. The reduced defect density and decreased ion migration lead to a higher p-channel charge carrier mobility of 0.7 cm2 V-1 s-1 , which is more than a threefold increase compared with the control device. Temperature-dependent charge transport studies demonstrate a mobility of 2.3 cm2 V-1 s-1 at 100 K due to the diminished ion mobility at low temperatures. This result illustrates that the additive strategy bears great potential to realize high-performance Sn-based perovskite FETs.

Multidentate Zwitterionic Ligand-Assisted Formation of Pure Bromide-Based Perovskite Nanosheets and Their Application in Blue Light-Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) have demonstrated rapid development during the past decade, whereas the inferior device performance of blue ones impedes the application in full-color display and lighting. Low-dimensional perovskites turn out to be the most promising blue-emitters owing to their superior stability. In this work, a multidentate zwitterionic l-arginine is proposed to achieve blue emission from pure bromide-based perovskites by in situ-forming low-dimensional nanosheets. First, l-arginine can promote the formation of perovskite nanosheets due to the strong interaction between the peripheral guanidinium cations and [PbBr6]4- octahedral layers, enabling a significant blue-shift. Second, the carboxyl group within l-arginine can passivate uncoordinated Pb2+ ions, improving the device performance. Finally, a blue PeLED is successfully constructed on the basis of the l-arginine-modulated perovskite film, demonstrating a peak luminance of 2152 cd/m2, an external quantum efficiency of 5.4%, and operation lifetime of 13.81 min. Further, the enlightenment from this work is hopefully to be applied in rationally designing spacer cations for low-dimensional perovskite optoelectronic devices.

Impact of organic amine cations on photoluminescence and magnetic properties in Dion-Jacobson hybrid manganese halide perovskites

A strenuous effort has been made to design multifunctional lead-free organic–inorganic hybrid (OIH) halide compounds, which are envisioned as next generation solar cell materials. However, it is challenging to design OIH halides that can exhibit both long-range magnetic ordering and high photoluminescence quantum yield (PLQY) since the dimensionality of the compounds has a contrasting effect on them. In this article, we have shown an approach to enhance PLQY in two-dimensional (2D) Heisenberg antiferromagnets by increasing the alkylene chain length of [H3N–(CH2)m–NH3]MnCl4 (m = 2, 3, and 4) compounds. All these compounds exhibit 2D layers of corner-sharing MnCl6 octahedra where the organic cations are intercalated between them. These compounds exhibit long-range antiferromagnetic ordering confirmed by the DC magnetic susceptibility and heat capacity measurements. The Néel temperature (TN) decreases with increasing the length of spacer cations due to a decrease in interlayer exchange interactions; however, interestingly, the lifetime of photoexcited electrons and PLQY enhances from 24 to 56 µs and 8% to 23%, respectively. Furthermore, the temperature-dependent photoluminescence measurements provide insight into thermal quenching and exciton binding energy. We believe this study can help to design new OIH halides with long-range magnetic ordering and high PLQY.

Selection of Functional Spacer Cations for Efficient 2D/3D Perovskite Solar Cells

Open AccessCCS ChemistryMINI REVIEWS18 Jan 2023Selection of Functional Spacer Cations for Efficient 2D/3D Perovskite Solar Cells Dengxue Li, Zhi Xing, Xiangchuan Meng, Xiaotian Hu, Ting Hu and Yiwang Chen Dengxue Li Google Scholar More articles by this author , Zhi Xing Google Scholar More articles by this author , Xiangchuan Meng Google Scholar More articles by this author , Xiaotian Hu Google Scholar More articles by this author , Ting Hu Google Scholar More articles by this author and Yiwang Chen Google Scholar More articles by this author https://doi.org/10.31635/ccschem.023.202202409 SectionsSupplemental MaterialAboutPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail In recent years, perovskite solar cells (PSCs) have gone through unparalleled rapid expansion and become a candidate for solar cell. Among various PSCs, though typical three-dimensional (3D) halide perovskite-based PSCs deliver the highest efficiency, they are subjected to severe instability, which constrains their commercialization applications. By comparison, the two-dimensional (2D) PSCs have aroused widespread concern due to their superior stability. After that, 2D/3D perovskite materials combining high efficiency and good stability emerge as the times require, which are expected to bring about stable and efficient PSCs. Here, this review focuses on selection of functional spacer cations for efficient and stable 2D/3D PSCs. First, the unique function of different spacer group and the selection of appropriate spacer cations in 2D perovskites was summarized and proposed. Then, by selecting appropriate cations, the role of 2D perovskite was elaborated, including energy level regulation, suppressing ion migration, defect passivation, releasing residual stress and improving stability. Besides, the preparation methods of 2D/3D perovskite were comprehensively summarized. Finally, current challenges and future opportunities for further development of 2D/3D perovskites for solar cells were discussed and prospected. Download figure Download PowerPoint Next article FiguresReferencesRelatedDetails Issue AssignmentNot Yet AssignedSupporting Information Copyright & Permissions© 2023 Chinese Chemical Society Downloaded 0 times PDF downloadLoading ...

The Effects of Mono- and Bivalent Linear Alkyl Interlayer Spacers on the Photobehavior of Mn(II)-Based Perovskites.

Mn(II)-based perovskite materials are being intensively explored for lighting applications; understanding the role of ligands regarding their photobehavior is fundamental for their development. Herein, we report on two Mn (II) bromide perovskites using monovalent (perovskite 1, P1) and bivalent (perovskite 2, P2) alkyl interlayer spacers. The perovskites were characterized with powder X-ray diffraction (PXRD), electron spin paramagnetic resonance (EPR), steady-state, and time-resolved emission spectroscopy. The EPR experiments suggest octahedral coordination in P1 and tetrahedral coordination for P2, while the PXRD results demonstrate the presence of a hydrated phase in P2 when exposed to ambient conditions. P1 exhibits an orange-red emission, while P2 shows a green photoluminescence, as a result of the different types of coordination of Mn(II) ions. Furthermore, the P2 photoluminescence quantum yield (26%) is significantly higher than that of P1 (3.6 %), which we explain in terms of different electron-phonon couplings and Mn-Mn interactions. The encapsulation of both perovskites into a PMMA film largely increases their stability against moisture, being more than 1000 h for P2. Upon increasing the temperature, the emission intensity of both perovskites decreases without a significant shift in the emission spectrum, which is explained in terms of an increase in the electron-phonon interactions. The photoluminescence decays fit two components in the microsecond regime-the shortest lifetime for hydrated phases and the longest one for non-hydrated phases. Our findings provide insights into the effects of linear mono- and bivalent organic interlayer spacer cations on the photophysics of these kinds of Mn (II)-based perovskites. The results will help in better designs of Mn(II)-perovskites, to increase their lighting performance.

Improving the brightness of quasi-2D perovskite light-emitting diode by controlling stoichiometric ratio of perovskite emission layer

The quasi-two-dimensional (quasi-2D) perovskite possesses good film coverage and high photoluminescence quantum efficiency, and exhibits a characteristic of high-level radiation recombination. However, the charge transferring from quasi-2D perovskites is not comparable to that of three-dimensional perovskites due to the insulating nature of large organic cations, thus limits the brightness of quasi-2D perovskite light-emitting diodes (PLEDs). In this work, phenylethylammonium bromide (PEABr) and formamidine hydrobromide (FABr) were strategically introduced as two spacer cations to form quasi-2D perovskite phase, thus weakened the van der Waals gap between individual perovskite layers. The enhanced coupling strength between each layer promoted the energy transfer efficiency and led to an increasing radiative recombination rate of the perovskite films. Meanwhile, an optimized molar ratio of PEABr: FABr: PbBr2 improved perovskite film morphology and passivated its defects, which reduced the nonradiative recombination loss of quasi-2D PLEDs. As a result, a maximum brightness of 32,368 cd m − 2 can be obtained for this kind of devices.

Photoluminescence Modulation of Ruddlesden-Popper Perovskite via Phase Distribution Regulation.

The intrinsic chaotic phase distribution in Ruddlesden-Popper Perovskite (RPP) hinders its further improvement of photoluminescence (PL) emission and limits its application in optical devices. In this work, we achieve the phase distribution regulation of RPP by varying the composition ratio of organic bulky spacer cations 1-naphthylmethylamine (NMA) and phenylethyl-ammonium (PEA), which is controllable and nondestructive for structures of RPP. By suppressing the small n-phase, the PL intensity emission of RPP is further improved. Through the time-resolved PL (TRPL) measurements, we find the PL lifetime of the sample with 66% PEA concentration increases with the temperature initially and possesses the highest values of τ1 and τ2 at ~255 K, indicating the immediate state assisting exciton radiative recombination, and it can be modulated by phase manipulation in RPP. The immediate state may outcompete other non-radiative decay channels for excited carriers, leading to the PL enhancement in RPP, and broadening its further application.

Toward Efficient Two-Photon Circularly Polarized Light Detection through Cooperative Strategies in Chiral Quasi-2D Perovskites.

Organic-inorganic hybrid perovskites carry unique semiconducting properties and advanced flexible crystal structures. These characteristics of organic-inorganic hybrid perovskites create a promising candidacy for circularly polarized light (CPL) detection. However, CPL detections based on chiral perovskites are limited to UV and visible wavelengths. The natural quantum well structures of layered hybrid perovskites generate strong light-matter interactions. This makes it possible to achieve near-infrared (NIR) CPL detection via two-photon absorption in the sub-wavelength region. In this study, cooperative strategies of dimension increase and mixed spacer cations are used to obtain a pair of chiral multilayered perovskites (R-β-MPA)EA2 Pb2 Br7 and (S-β-MPA)EA2 Pb2 Br7 (MPA = methylphenethylammonium and EA = ethylammonium). The distinctive bi-cations interlayer and multilayered inorganic skeletons provide enhanced photoconduction. Moreover, superior photoconduction leads to the prominent NIR CPL response with a responsivity up to 8.1 × 10-5 A W-1 . It is anticipated that this work can serve as a benchmark for the fabrication and optimization of efficient NIR CPL detection by simple chemical design.

Spacer cation engineering in Ruddlesden-Popper perovskites for efficient red light-emitting diodes with recommendation 2020 color coordinates

Ruddlesden-Popper perovskites (RPPs) have been demonstrated as a very promising approach for tuning the emission color of perovskite light-emitting diodes (PeLEDs). However, achieving high-performance red PeLEDs with recommendation 2020 color coordinates is still challenging due to the lack of reasonable control over the properties of RPP films. Here, we demonstrate that the judicious selection of spacer cations in RPPs affords a lever for engineering their film properties, including phase distribution, energy funneling process, trap density, and carrier mobility. Four structurally related spacer cations, benzylammonium (BZA), phenylethylammonium (PEA), 3-phenyl-1-propylammonium (PPA), and phenoxyethylammonium (POEA), are studied. Owing to narrow phase distribution, efficient energy funneling, and low trap density, the POEA-based RPP films enable efficient red PeLEDs with a peak external quantum efficiency of 10.3%, a maximum brightness of 1052 cd m−2, and excellent spectral stability. Significantly, the electroluminescence spectrum represents CIE 1931 color coordinates of (0.71, 0.29), which meets the recommendation 2020 standard (0.708, 0.292). The findings provide useful guidelines for the rational design of new organic spacer cations for RPPs with high performance.

Spacer-Dependent and Pressure-Tuned Structures and Optoelectronic Properties of 2D Hybrid Halide Perovskites.

Compared with their 3D counterparts, 2D hybrid organic-inorganic halide perovskites (HOIPs) exhibit enhanced chemical stabilities and superior optoelectronic properties, which can be further tuned by the application of external pressure. Here, we report the first high-pressure study on CMA2PbI4 (CMA = cylcohexanemethylammonium), a 2D HOIP with a soft organic spacer cation containing a flexible cyclohexyl ring, using UV-visible absorption, photoluminescence (PL) and vibrational spectroscopy, and synchrotron X-ray microdiffraction, all aided with density functional theory (DFT) calculations. Substantial anisotropic compression behavior is observed, as characterized by unprecedented negative linear compressibility along the b axis. Moreover, the pressure dependence of optoelectronic properties is found to be in strong contrast with those of 2D HOIPs with rigid spacer cations. DFT calculations help to understand the compression mechanisms that lead to pressure-induced bandgap narrowing. These findings highlight the important role of soft spacer cations in the pressure-tuned optoelectronic properties and provide guidance to the design of new 2D HOIPs.

Band gap engineering and optoelectronic properties of all-inorganic Ruddlesden-Popper halide perovskites Cs2B(X1-uYu)4 (B = Pb, Sn; X/Y = Cl, Br, I)

In this article two-dimensional Ruddlesden-Popper (2DRP) halide perovskites Cs2B(X1-uYu)4 where B = Pb, Sn; X/Y = Cl, Br, I; and u = 0, 0.25, 0.5, 0.75, 1 are investigated for potential applications in optoelectronic, photoemission and photovoltaic devices. In these compounds the corner sharing B-centered [BX2Y4]4- units build the 2D [BX2Y2]n2n− plane, where the halides occupy the in-plane bridging and out of plane apical site respectively, while the spacer cation (Cs+) balancing the charge and separate the octahedral layers. These compounds have direct band gaps and spin orbit (SOC) calculations split Pb/Sn p-orbital and reduce the band gaps. The wide (1.04–3.45) and direct band gaps enable these materials for futuristic applications in optoelectronics, high speed ultrathin transistors and photodetectors. The anti-bonding lone-pair Pb/Sn-s orbital at the valence band edge is excellent for light absorption and photovoltaic performance. These compounds are good dielectric and optically functional materials for photovoltaic and energy storage devices due to their small values of charge carrier effective masses and large exciton binding energies. Therefore, the optical coefficients like dielectric function (real and imaginary), absorption coefficient and index of refraction are calculated.

Pressure-induced distinct excitonic properties of 2D perovskites with isomeric organic molecules for spacer cations.

Spacer organic cations in two-dimensional (2D) perovskites play vital roles in inducing structural distortion of the inorganic components and dominating unique excitonic properties. However, there is still little understanding of spacer organic cations with identical chemical formulas, and different configurations have an impact on the excitonic dynamics. Herein, we investigate and compare the evolution of the structural and photoluminescence (PL) properties of [CH3(CH2)4NH3]2PbI4 ((PA)2PbI4) and [(CH3)2CH(CH2)2NH3]2PbI4 ((PNA)2PbI4) with isomeric organic molecules for spacer cations by combining steady-state absorption, PL, Raman and time-resolved PL spectra under high pressures. Intriguingly, the band gap is continuously tuned under pressure and decreased to 1.6 eV at 12.5 GPa for (PA)2PbI4 2D perovskites. Simultaneously, multiple phase transitions occur and the carrier lifetimes are prolonged. In contrast, the PL intensity of (PNA)2PbI4 2D perovskites exhibits an almost 15-fold enhancement at 1.3 GPa and an ultrabroad spectral range of up to 300 nm in the visible region at 7.48 GPa. These results indicate that the isomeric organic cations (PA+ and PNA+) with different configurations significantly mediate distinct excitonic behaviors due to different resilience to high pressures and reveal a novel interaction mechanism between organic spacer cations and inorganic layers under compression. Our findings not only shed light on the vital roles of isomeric organic molecules as organic spacer cations in 2D perovskites under pressure, but also open a route to rationally design highly efficient 2D perovskites incorporating such spacer organic molecules in optoelectronic devices.

Photogenerated charge transfer in Dion-Jacobson type layered perovskite based on naphthalene diimide.

Incorporating organic semiconducting spacer cations into layered lead halide perovskite structures provides a powerful approach to mitigate the typical strong dielectric and quantum confinement effects by inducing charge-transfer between the organic and inorganic layers. Herein we report the synthesis and characterization of thin films of novel DJ-phase organic-inorganic layered perovskite semiconductors using a naphthalene diimide (NDI) based divalent spacer cation, which is shown to accept photogenerated electrons from the inorganic layer. With alkyl chain lengths of 6 carbons, an NDI-based thin film exhibited electron mobility (based on space charge-limited current for quasi-layered 〈n〉 = 5 material) was found to be as high as 0.03 cm2 V-1 s-1 with no observable trap-filling region suggesting trap passivation by the NDI spacer cation.

Energy level alignments between organic and inorganic layers in 2D layered perovskites: conjugation vs. substituent.

2D layered hybrid perovskites have attracted huge attention due to their interesting optoelectronic properties and chemical flexibility. Depending upon their electronic structures and properties, these materials can be utilised in various optoelectronic devices like photovoltaics, LEDs and so on. In this context, study of the excited energy levels of the organic spacers can help us to align the excited energy levels of the organic unit with the excitonic level of the inorganic unit according to the requirement of a particular optoelectronic device. We have explored the role of 3-phenyl-2-propenammonium on the electronic structure of a perovskite containing this cation as a spacer. Our results clearly demonstrate the active participation of conjugated ammonium spacers in the electronic structure of a perovskite. Also, we have considered a variety of amines to identify the best alignment with common inorganic units and studied the role of substituents and conjugation on the energy level alignment. Placing the triplet excited level of an organic spacer below the lowest excitonic level of the inorganic unit can induce energy transfer from the inorganic to organic unit, finally resulting in phosphorescence emission. We have shown that the triplet energy level of 3-anthracene-2-propeneamine/3-pyrene-2-propeneamine can be tuned in such a way that there can be an excitonic energy transfer from the Pb2I7/PbI4 inorganic unit-based perovskites. Therefore, perovskite material with such combinations of organic spacer cations will be very useful for light emission applications.

Tuning charge carrier dynamics through spacer cation functionalization in layered halide perovskites: an ab initio quantum dynamics study

Fluorination of spacer cations compacts the layered halide perovskites, weakens the electron–phonon interactions, and suppresses the non-radiative charge carrier recombination processes.

Stabile fluoro-benzene-based spacer for lead-free Dion-Jacobson perovskites.

Two-dimensional perovskite materials have been investigated as potential candidates for next-generation-wide band gap devices and lead-based perovskites are the most common materials within two-and three-dimensional structures due to their superior optoelectronic properties. Nevertheless, the stability and toxic element issues are the two significant shortcomings of device commercialization. The fluoro-benzene-based divalent ammonium spacer cations and replacing Zn2+ with Pb2+ will improve the two-dimensional perovskite stability. These stable lead-free wide band gap two-dimensional structures have better carrier mobility at high-temperature regions. Therefore, lead-free two-dimensional perovskites might be suitable for higher temperatures optoelectronic applications.

Enhanced UV stability of 2D perovskites (HO(CH2)4NH3)2(MA)n−1PbnI3n+1 due to hydrogen bonding

The 2D perovskites (HO(CH2)4NH3)2(MA)n−1PbnI3n+1 showed improved UV stability due to the hydrogen bonds between the hydroxyl groups of the organic spacer cations HO(CH2)4NH3+, compared with that of (CH3(CH2)3NH3)2PbI4 without the hydrogen bonds.

Strain relaxation and phase regulation in quasi-2D perovskites for efficient solar cells

By introducing F-PEA as a second spacer cation, a remarkable PCE of 17.17% is achieved for iso-BA based Q-2D PSCs with PTAA as a hole transport layer, attributed to the released tensile strain and improved charge transport in the iso-BA:F-PEA based film.