Low-dimensional hybrid perovskites containing an organic cation with an extended conjugated system : tuning the excitonic absorption features

Low-dimensional hybrid perovskites are receiving increased attention. One of the advantages of the low-dimensional hybrids over their 3D counterparts is their greater structural flexibility towards the incorporation of bigger, more complex, organic cations. In this communication, we introduce a pyrene derivative as an organic cation containing an extended pi-system for use in a variety of low-dimensional hybrids. We show that materials with different excitonic absorption features can be obtained by tuning the iodide/lead ratio in the precursor solutions, using the same pyrene cation. In this way, hybrids with optical characteristics corresponding to 2D, 1D and 0D hybrid perovskites are obtained. The formation and thermal stability of the different hybrids is analysed and compared

2D layered perovskite containing functionalised benzothieno-benzothiophene molecules : formation, degradation, optical properties and photoconductivity

2D layered hybrid perovskites are currently in the spotlight for applications such as solar cells, light-emitting diodes, transistors and photodetectors. The structural freedom of 2D layered perovskites allows for the incorporation of organic cations that can potentially possess properties contributing to the performance of the hybrid as a whole. In this study, we incorporated a benzothieno[3,2-b]benzothiophene (BTBT) alkylammonium cation into the organic layer of a 2D layered lead iodide perovskite. The formation and degradation of this material are discussed in detail. It is shown that the use of a solvent vapour annealing method significantly enhances the absorption, emission and crystallinity of films of this 2D layered perovskite as compared to regular thermal annealing. The photoconductivity of the films was determined using time-resolved microwave conductivity (TRMC) as well as in a device. In both cases, the solvent vapour annealed films show markedly higher photoconductivity than the films obtained using the regular thermal annealing approach

Low‐Dimensional Hybrid Perovskites Containing an Organic Cation with an Extended Conjugated System: Tuning the Excitonic Absorption Features

Low-dimensional hybrid perovskites are receiving increased attention. One of the advantages of the low-dimensional hybrids over their 3D counterparts is their greater structural flexibility towards the incorporation of bigger, more complex, organic cations. In this communication, we introduce a pyrene derivative as an organic cation containing an extended pi-system for use in a variety of low-dimensional hybrids. We show that materials with different excitonic absorption features can be obtained by tuning the iodide/lead ratio in the precursor solutions, using the same pyrene cation. In this way, hybrids with optical characteristics corresponding to 2D, 1D and 0D hybrid perovskites are obtained. The formation and thermal stability of the different hybrids is analysed and compared

Directing the self-assembly of conjugated organic ammonium cations in low-dimensional perovskites by halide substitution

At present, two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) are drawing significant interest because of their potential use in different optoelectronic applications, that is, photovoltaics and photodetectors. Here, we report on a series of 2D layered HOIPs (Bit-C3)(2)PbX4 (with X = Cl, Br, and I) containing a 2,2'-bithiophene chromophore functionalized with a propylammonium tethering chain as a model molecule. The optical properties, crystal structure, and phase behavior of the 2D layered HOIPs are studied in depth. The crystal structures with the chemical formula (Bit-C3)(2)PbX4 (with X = Cl, and Br) are successfully obtained. Contrastingly, different crystal structures with an inorganic framework containing face- and corner-sharing octahedra were identified for the iodide-based HOIP. The phase diversity and thermal stability of the (Bit-C3)(2)PbX4 (with X = Cl, Br, and I) thin films were investigated via in situ measurements. Here, the presence of lower-dimensional hybrids with reduced electronic dimensionality within the iodide-based thin film is demonstrated. Additionally, we show that the 2D hybrid thermal stability is dependent on the type of lead(II)halide framework employed. We suggest that, via halide substitution from iodide to bromide and chloride, the molecular degrees of freedom of the Bit-C3 ammonium cations are reduced by spatial confinement of a smaller inorganic framework, therefore, limiting the formation of lower-dimensional hybrids besides the targeted 2D layered HOIP. This study illustrates the importance of efficiently utilizing the space supplied by the inorganic framework in which the organic ammonium cations can reside within a 2D layered HOIP. This, in turn, dictates how the organic ammonium cations arrange themselves within the organic layer and influences the adopted crystal structure of the hybrid

Study on the dynamics of phase formation and degradation of 2D layered hybrid perovskites and low‐dimensional hybrids containing mono‐functionalized oligothiophene cations

Low-dimensional (2D or 1D) hybrid perovskites are receiving increased attention due to their structural flexibility and enhanced stability compared to their 3D counterparts. Understanding the phase formation and degradation behavior of these materials is crucial towards their use in optoelectronic devices, since different crystal phases possess different optical and electronic properties. In this communication, we study the phase formation and degradation of a series of hybrids containing bithiophene, terthiophene and quaterthiophene derivatives. We show that two crystal phases can be formed for each of these systems, depending on the processing conditions. One phase corresponds to a 2D layered perovskite and the other phase has optical properties corresponding to a dimensionality intermediate between a 2D and a 1D hybrid

Study on the dynamics of phase formation and degradation of 2D layered hybrid perovskites and low-dimensional hybrids containing mono-functionalized oligothiophene cations

Low-dimensional (2D or 1D) hybrid perovskites are receiving increased attention due to their structural flexibility and enhanced stability compared to their 3D counterparts. Understanding the phase formation and degradation behavior of these materials is crucial towards their use in optoelectronic devices, since different crystal phases possess different optical and electronic properties. In this communication, we study the phase formation and degradation of a series of hybrids containing bithiophene, terthiophene and quaterthiophene derivatives. We show that two crystal phases can be formed for each of these systems, depending on the processing conditions. One phase corresponds to a 2D layered perovskite and the other phase has optical properties corresponding to a dimensionality intermediate between a 2D and a 1D hybrid

2D layered perovskite containing functionalised benzothieno-benzothiophene molecules: Formation, degradation, optical properties and photoconductivity

2D layered hybrid perovskites are currently in the spotlight for applications such as solar cells, light-emitting diodes, transistors and photodetectors. The structural freedom of 2D layered perovskites allows for the incorporation of organic cations that can potentially possess properties contributing to the performance of the hybrid as a whole. In this study, we incorporated a benzothieno[3,2-b]benzothiophene (BTBT) alkylammonium cation into the organic layer of a 2D layered lead iodide perovskite. The formation and degradation of this material are discussed in detail. It is shown that the use of a solvent vapour annealing method significantly enhances the absorption, emission and crystallinity of films of this 2D layered perovskite as compared to regular thermal annealing. The photoconductivity of the films was determined using time-resolved microwave conductivity (TRMC) as well as in a device. In both cases, the solvent vapour annealed films show markedly higher photoconductivity than the films obtained using the regular thermal annealing approach.ChemE/Opto-electronic Material

Degradation of the Formamidinium Cation and the Quantification of the Formamidinium–Methylammonium Ratio in Lead Iodide Hybrid Perovskites by Nuclear Magnetic Resonance Spectroscopy

The highest efficiency in perovskite solar cells is currently achieved with mixed-cation hybrid perovskites. The ratio in which the cations are present in the perovskite structure has an important effect on the optical properties and the stability of these materials. At present, the formamidinium cation is an integral part of many of the highest efficiency perovskite systems. In this work, we introduce a nuclear magnetic resonance (NMR) spectroscopy protocol for the identification and differentiation of mixed perovskite phases and of a secondary phase due to formamidinium degradation. The influence of the cooling rate used in a precipitation method on the FA/MA ratio in formamidinium–methylammonium lead iodide perovskites (FA_<i>x</i>MA_1–<i>x</i>PbI₃) was investigated and compared to the FA/MA ratio in thin films. In order to obtain the FA/MA ratio from fast and accessible liquid-state ¹H NMR spectra, the influence of the acidity of the solution on the line width of the resonances was elucidated. The ratio of the organic cations incorporated into the perovskite structure could be reliably quantified in the presence of the secondary phase through a combination of liquid-state ¹H NMR and solid-state ¹³C NMR spectroscopic analysis

3D Perovskite Passivation with a Benzotriazole-Based 2D Interlayer for High-Efficiency Solar Cells.

2H-Benzotriazol-2-ylethylammonium bromide and iodide and its difluorinated derivatives are synthesized and employed as interlayers for passivation of formamidinium lead triiodide (FAPbI3) solar cells. In combination with PbI2 and PbBr2, these benzotriazole derivatives form two-dimensional (2D) Ruddlesden-Popper perovskites (RPPs) as evidenced by their crystal structures and thin film characteristics. When used to passivate n-i-p FAPbI3 solar cells, the power conversion efficiency improves from 20% to close to 22% by enhancing the open-circuit voltage. Quasi-Fermi level splitting experiments and scanning electron microscopy cathodoluminescence hyperspectral imaging reveal that passivation provides a reduced nonradiative recombination at the interface between the perovskite and hole transport layer. Photoluminescence spectroscopy, angle-resolved grazing-incidence wide-angle X-ray scattering, and depth profiling X-ray photoelectron spectroscopy studies of the 2D/three-dimensional (3D) interface between the benzotriazole RPP and FAPbI3 show that a nonuniform layer of 2D perovskites is enough to passivate defects, enhance charge extraction, and decrease nonradiative recombination

3D Perovskite Passivation with a Benzotriazole-Based 2D Interlayer for High-Efficiency Solar Cells

2H-Benzotriazol-2-ylethylammonium bromide and iodide and its difluorinated derivatives are synthesized and employed as interlayers for passivation of formamidinium lead triiodide (FAPbI3) solar cells. In combination with PbI2 and PbBr2, these benzotriazole derivatives form two-dimensional (2D) Ruddlesden-Popper perovskites (RPPs) as evidenced by their crystal structures and thin film characteristics. When used to passivate n-i-p FAPbI3 solar cells, the power conversion efficiency improves from 20% to close to 22% by enhancing the open-circuit voltage. Quasi-Fermi level splitting experiments and scanning electron microscopy cathodoluminescence hyperspectral imaging reveal that passivation provides a reduced nonradiative recombination at the interface between the perovskite and hole transport layer. Photoluminescence spectroscopy, angle-resolved grazing-incidence wide-angle X-ray scattering, and depth profiling X-ray photoelectron spectroscopy studies of the 2D/three-dimensional (3D) interface between the benzotriazole RPP and FAPbI3 show that a nonuniform layer of 2D perovskites is enough to passivate defects, enhance charge extraction, and decrease nonradiative recombination