Lead-free Hybrid Perovskites Research Articles

Pyro-phototronic Effect Enhanced Self-Powered Photoresponse in Lead-Free Hybrid Perovskite.

Pyro-phototronic effect (PPE) can significantly boost the performance of hybrid perovskite (HPs) photodetectors due to the effective modulation of photogenerated charge carrier separations, transportation, and extraction. However, there are few reports on the application of PPE in lead-free HPs. Herein, a polar lead-free HP (1,3-BMACH)BiBr5 [1,3-BMACH = 1,3-bis(aminomethyl)cyclohexane] is synthesized and realized broadband self-powered photoresponse from X-rays to near-infrared (NIR) through the PPE. Particularly, this light-induced PPE in lead-free HPs breaks the limitation of the optical band gap, making them suitable for broadband self-powered photodetection. Under 405 nm illumination, compared with a purely photovoltaic system, Iphoto+pyro is boosted by 3100%, and R and D* are both enhanced by 260% after coupled PPE. It is particularly interesting that an obvious X-ray-induced PPE phenomenon is also observed, which endows (1,3-BMACH)BiBr5 with a high sensitivity of 154 μC Gy-1 cm-2 and a low detection limit of 307 nGy s-1 under the self-powered mode. The implementation of light-induced PPE from X-rays to NIR in lead-free HPs provides a new approach for constructing environmentally friendly, broadband, and self-powered optoelectronic devices in the future.

Durable Photo-Pyroelectric Detection in a Diamine-Constructed Lead-Free Hybrid Perovskite Ferroelectric.

As a subcategory of pyroelectric materials, hybrid perovskite ferroelectrics possess substantial pyroelectric properties and exceptional light absorption characteristics, demonstrating significant potential in the photo-pyroelectric (PPE) detection field. Despite the significant advantages of hybrid perovskite ferroelectric materials for PPE detection, both the lead issue and the weak stability from van der Waals interactions in monoamines have hindered their further application. Here, 1D lead-free ferroelectric (BDA)SbBr5 (1, where BDA is 1,4-butanediammonium) is fabricated to achieve PPE detection. Compound 1 exhibits significant symmetry breaking attributed to the order-disorder transition of organic cations and octahedral distortions. Specifically, compound 1 enables broad-spectrum PPE detection from UV to near-infrared (377-980nm) and further realizes switchable pyroelectric current after polarization. More importantly, the stability of the pyroelectric current is preserved without degradation over three months, attributed to the hydrogen bonding interactions of butanediamide. Further theoretical calculations of compound 1 reveal a more negative energy of formation than its monoamine homologs (BA)2SbBr5 (where BA is n-butylammonium), which is evidence of its stability. These findings highlight 1 as a promising candidate for high-stability and environmentally friendly PPE wide-spectrum detection, representing a noteworthy advancement in the ferroelectric field.

Narrow-Bandgap Tellurium-Based Chiral Hybrid Perovskite Single Crystals with Rashba-Dresselhaus Effect and Piezoelectricity.

Chiral hybrid perovskites have aroused great interest due to their unique versatile properties. However, designing chiral perovskites with narrow bandgaps is challenging, with their electronic properties such as the Rashba-Dresselhaus effect and piezoelectricity remaining unclear. Herein, single crystals of zero-dimensional (0D) tellurium-based chiral hybrid perovskite, (R-/S-α-PEA)2TeI6 and (R-/S-α-PEA)2TeBr6 (PEA = phenylethylammonium), with sizes of over 5 mm are grown by seed-crystal-assisted solution-temperature-lowering. The optical bandgaps are about 1.60 and 2.18 eV for the iodide and bromide analogues, respectively, which are the lowest among various chiral lead-free hybrid perovskites with the same halide ions in the X-site to the best of our knowledge. First-principles calculations reveal that (R-/S-α-PEA)2TeBr6 shows a larger Rashba-Dresselhaus spin-splitting than (R-/S-α-PEA)2TeI6, probably thanks to the greater distortion of [TeBr6] octahedra. Moreover, the piezoelectric coefficients d33 of (R-/S-α-PEA)2TeI6 and (R-/S-α-PEA)2TeBr6 are about 2.6 and 1.8 pC N-1, respectively. This work deepens the understanding of physical properties of 0D tellurium-based chiral perovskites with potential multifunctionality, including spintronic and piezoelectric performances.

Band-Gap Narrowing and Electric Transport Regulation of Hybrid Perovskites via Pressure Engineering.

Lead-free organic-inorganic hybrid perovskites are one class of promising optoelectronic materials that have attracted much attention due to their outstanding stability and environmentally friendly nature. However, the intrinsic band gap far from the Shockley-Queisser limit and the inferior electrical properties largely limit their applicability. Here, a considerable band-gap narrowing from 2.43 to 1.64 eV with the compression rate up to 32.5% is achieved via high-pressure engineering in the lead-free hybrid perovskite MA3Sb2I9. Meanwhile, the electric transport process changes from the initial interaction of both ions and electrons to only the contribution of electrons upon compression. The alteration in electrical characteristics is ascribed to the vibration limitation of organic ions and the enhanced orbital overlap, resulting from the reduction of the Sb-I bond length through pressure-induced phase transitions. This work not only systematically investigates the correlation between the structural and optoelectronic properties of MA3Sb2I9 but also provides a potential pathway for optimizing electrical properties in lead-free hybrid perovskites.

Exploring the potential applications of lead-free organic–inorganic perovskite type [NH3(CH2)nNH3]MCl4 (n = 2, 3, 4, 5, and 6; M = Mn, Co, Cu, Zn, and Cd) crystals

The organic–inorganic hybrid perovskite compounds have been extensively studied since the dawn of a new era in the field of photovoltaic applications. Up to now, perovskites have proven to be the most promising in terms of power conversion efficiency; however, their main disadvantages for use in solar cells are toxicity and chemical instability. Therefore, it is essential to develop a hybrid perovskite that can be replaced with lead-free materials. This review focuses on the possibility of applying lead-free organic–inorganic perovskite types [NH3(CH2)nNH3]MCl4 (n = 2, 3, 4, 5, and 6; M = Mn, Co, Cu, Zn, and Cd) crystals. We are seeking organic–inorganic hybrid perovskite materials with very high temperature stability or without phase transition temperature, and thermal stability. Thus, by considering the characteristics according to the methylene lengths and the various transition metals, we aim to identify improved materials meeting the criteria mentioned above. Consequently, the physicochemical properties of organic–inorganic hybrid perovskite [NH3(CH2)nNH3]MCl4 regarding the effects of various transition metal ions of the anion and the methylene lengths of the cation are expected to promote the development and application of lead-free hybrid perovskite solar cells.

Piezoelectricity of lead-free hybrid perovskite monolayer (ATHP)2XY4 (X = Ge, Sn; Y = Cl, Br, I): Cross-scale calculation and simulation

Two-dimensional (2D) piezoelectric material is the core part of all kinds of micro-piezoelectric devices (piezoelectric energy harvesters, piezoelectric sensors, etc.). Based on the first principle, this paper theoretically predicts a kind of organic–inorganic lead-free hybrid perovskite monolayer (ATHP)2XY4 (X = Ge, Sn; Y = Cl, Br, I) with a large out-of-plane piezoelectric coefficient (d31). Combined with the finite element simulation, it shows excellent performance in the piezoelectric energy harvester. Through the first-principles theoretical calculation, the density, elastic tensor, piezoelectric stress tensor, and dielectric coefficient of the (ATHP)2XY4 monolayer can be obtained. The thermodynamic stability and mechanical stability of the materials are judged by ab initio molecular dynamics and stress–strain relationship analysis, respectively. The piezoelectric coefficient of the material is calculated, in which the d31 of (ATHP)2SnBr4 is the largest (d31 = 35.04 pm/V), which is still 7 times that of the bulk AlN and at least one order of magnitude larger than that of other 2D materials. The finite element simulation results of a simple piezoelectric beam show that the voltage output of the piezoelectric beam reaches 27.79 V. Our research shows that lead-free hybrid perovskite monolayer (ATHP)2XY4 has strong competitiveness in the application of environment-friendly and bio-friendly micro-piezoelectric devices. In addition, the cross-scale simulation method from the first principles to the finite element method is of great significance for the optimization of micro-piezoelectric devices.

A Polar Two-Dimensional Lead-Free Hybrid Perovskite for Self-Powered Polarization-Sensitive Photodetection

Two-dimensional (2D) lead hybrid perovskites have attracted great attention due to their excellent stability and unique physical and chemical properties. Nevertheless, the toxicity of lead remains an urgent issue. Lead-free...

Structural geometry and molecular dynamics by nuclear magnetic resonance of organic-inorganic perovskite [NH3(CH2)6NH3]CuBr4 crystal near phase transition temperature

The structural, thermal, and physical properties of newly developed lead-free hybrid perovskite solar cells are discussed for [NH3(CH2)6NH3]CuBr4. The hybrid material undergoes a phase transition at 269 K (TC), and is thermodynamically stable until approximately 472 K. The crystal structure determined by single-crystal X-ray diffraction is monoclinic and triclinic above and below TC, respectively. The 1H and 13C nuclear magnetic resonance spectra, recorded as a function of the temperature, revealed considerable changes in the 1H chemical shifts of NH3 and the 13C chemical shifts of the carbon atoms close to N as a result of the structural phase transition. The large difference in the activation energy, obtained from the 13C spin-lattice relaxation time above and below TC, also appears to be related to energy transfer changes in 13C. The thermal stabilities of [NH3(CH2)nNH3]CuBr4 (n = 3, 4, and 6) were compared by varying the number of methylene units, and the temperature with 2 % weight loss was shown to decrease as the number of methylene units increases. This in-depth analysis of the physical properties is expected to promote the development and application of lead-free hybrid perovskite solar cells.

Spectroscopic Evidence of Localized Small Polarons in Low-Dimensional Ionic Liquid Lead-Free Hybrid Perovskites.

Rational design is an important approach to consider in the development of low-dimensional hybrid organic-inorganic perovskites (HOIPs). In this study, 1-butyl-1-methyl pyrrolidinium (BMP), 1-(3-aminopropyl)imidazole (API), and 1-butyl-3-methyl imidazolium (BMI) serve as prototypical ionic liquid components in bismuth-based HOIPs. Element-sensitive X-ray absorption spectroscopy measurements of BMPBiBr4 and APIBiBr5 reveal distinct resonant excitation profiles across the N K-edges, where contrasting peak shifts are observed. These 1D-HOIPs exhibit a large Stokes shift due to the small polaron contribution, as probed by photoluminescence spectroscopy at room temperature. Interestingly, the incorporation of a small fraction of tin (Sn) into the APIBiBr5 (Sn/Bi mole ratio of 1:3) structure demonstrates a strong spectral weight transfer accompanied by a fast decay lifetime (2.6 ns). These phenomena are the direct result of Sn-substitution in APIBiBr5, decreasing the small polaron effect. By changing the active ionic liquid, the electronic interactions and optical responses can be moderately tuned by alteration of their intermolecular interaction between the semiconducting inorganic layers and organic moieties.

Structure characterization and physical properties of some novel lead-free hybrid perovskites for multifunctional applications

Structure characterization and physical properties of some novel lead-free hybrid perovskites for multifunctional applications

The effect of cations in electronic, and optical properties of lead-free halide perovskites based on Sn–Ge

In this work, the electronic and optical properties of three-dimensional (3D) lead-free hybrid perovskites [Formula: see text][Formula: see text] with organic and inorganic cations [Formula: see text], Cs ([Formula: see text]) have been investigated using density functional theory (DFT). The nature of the cations in the 3D perovskite structure has a significant impact on the electronic and optical properties of the 3D structures because octahedral [Formula: see text] is so sensitive to them. The results revealed that by replacing the organic cation with the inorganic cation, the band gap has increased, and also in the optical properties, an increase in the absorption coefficient and a decrease in reflection have been observed. According to the obtained results, the [Formula: see text] compound is a better candidate for optoelectronic devices and solar cells applications than [Formula: see text], due to its higher band gap, higher absorption coefficient, lower reflection, and cheaper price. These findings are crucial for comprehending how cations affect lead-free perovskite halides, and we hope it will be a useful guide for improving the photovoltaic efficiency of lead-free perovskite solar cells. In addition to the absorber layer of solar cells, 3D perovskites are used in laser and thermoelectric applications, topological insulation, and radiation detection.

Spectrally Selective Polarization-Sensitive Photodetection Based on a 1D Lead-Free Hybrid Perovskite Ferroelectric

Green, self-powered, flexible, and tunable features have been greatly desired to satisfy the increasing demands for next-generation photodetectors and sensors. Here, we report a 1D lead-free perovskite ferroelectric HDA-BiI5 (HDA = hexane-1,6-diammonium) based photodetector showing a spectrally selective linear polarized light response due to a unique linear dichroic conversion behavior. The HDA-BiI5 single crystal device shows an orthogonal reverse of polarization-sensitive photocurrent and can distinguish linearly polarized light in different wavelength ranges with the photocurrent anisotropy ratio ω of about 1.37 at 405 nm, 1.00 at 490 nm, and 1.17 at 530 nm. Importantly, the device achieves a ferroelectricity-driven self-powered detection with an excellent ω (∼1.28 at 405 nm) and a high detectivity D* of 5.3 × 108 Jones. This research provides a pathway for the design of future integratable polarization-sensitive photodetectors.

Centimeter-Sized Piezoelectric Single Crystal of Chiral Bismuth-Based Hybrid Halide with Superior Electrostrictive Coefficient.

The lead-free hybrid perovskite piezoelectrics possess advantages of easy processing, light weight, and low-toxicity over inorganic ceramics. However, the lack of understanding in structure-property relationships hinders exploration of new molecular piezoelectric crystals with excellent performances. Herein, by introducing chiral α-phenylethylammonium (α-PEA+ ) cations into bismuth-based hybrid halides, centimeter-sized (R-α-PEA)4 Bi2 I10 and (S-α-PEA)4 Bi2 I10 single crystals with a superior piezoelectric voltage coefficient g22 of 309mV m N-1 , are obtained. Structural rigidity in crystals leads to a remarkable electrostrictive coefficient Q22 of 25.8 m4 C-2 , nearly 20 times higher than that of poly(vinylidene fluoride) (PVDF), which is beneficial to improve piezoelectricity with the synergistic effect of chirality. Moreover, the as-grown crystals show outstanding phase stability from 173 K to ≈470 K. This work suggests a design strategy based on rigidity and chirality to exploit novel piezoelectrics among hybrid metal halides.

One-dimensional lead-free perovskite single crystals with high X-ray response grown by liquid phase diffusion

A liquid phase diffusion method has been developed. Adopting this method, large-sized lead-free hybrid perovskite (1,5-pentanediamine)BiI5 single-crystals were obtained, exhibiting a high X-ray response sensitivity of 8120 μC Gyair−1 cm−2 at −80 V.

0D triiodide hybrid halide perovskite for X-ray detection.

In the relentless pursuit of developing high-performance, stable and environmentally friendly materials for X-ray detection, we present a new class of Bi-based hybrid organic-inorganic perovskites. An X-ray detector based on a new zero-dimensional (0D) triiodide-induced lead-free hybrid perovskite, (DPA)2BiI9 (DPA = C5H16N22+), has been developed demonstrating outstanding detection performance, including high X-ray sensitivity (20 570 μC Gyair-1 cm-2), low detectable dose rate (0.98 nGyair s-1), fast response time (154/162 ns) and excellent long-term stability.

A two-dimensional lead-free hybrid perovskite semiconductor with reduced melting temperature.

1-Methylhexylammonium tin iodide yields the lowest reported melting temperature (Tm = 142 °C) to date among lead-free hybrid perovskite semiconductors. Molecular branching near the organic ammonium group coupled with tuning of metal/halogen character suppresses Tm and facilitates effective melt-based deposition of films with 568 nm absorption onset.

Self-Assembly of 2D Hybrid Double Perovskites on 3D Cs2 AgBiBr6 Crystals towards Ultrasensitive Detection of Weak Polarized Light.

We report the self-assembly of 2D double perovskite (BLA)2 CsAgBiBr7 (BLA=benzylammonium) on 3D Cs2 AgBiBr6 crystals, providing the first demonstration of polarization-sensitive photodetection using lead-free double perovskite heterocrystals (HCs). The (BLA)2 CsAgBiBr7 /Cs2 AgBiBr6 HC successfully combines the anisotropy of 2D double perovskites with the well-defined interface provided by heterogeneous integration. Driven by the built-in electric field in junction, photodetectors of HCs exhibit unique polarization dependence of zero-bias photocurrent with a large anisotropy ratio up to 9, which is 6 times amplified as compared to the pristine 2D (BLA)2 CsAgBiBr7 . More importantly, the present devices can remain polarization-sensitive with incident light intensity down to the nW cm-2 level. Our study on lead-free hybrid perovskite HCs marks a step toward establishing robust material foundations for fundamental scientific investigations and the development of optoelectronic devices.

Advances in physicochemical characterization of lead-free hybrid perovskite [NH3(CH2)3NH3]CuBr4 crystals

To support the development of eco-friendly hybrid perovskite solar cells, structural, thermal, and physical properties of the lead-free hybrid perovskite [NH3(CH2)3NH3]CuBr4 were investigated using X-ray diffraction (XRD), differential scanning calorimetry, thermogravimetric analysis, and nuclear magnetic resonance spectroscopy. The crystal structure confirmed by XRD was monoclinic, and thermodynamic stability was observed at approximately 500 K without any phase transition. The large changes in the 1H chemical shifts of NH3 and those in C2 close to N are affected by N–H∙∙∙Br hydrogen bonds because the structural geometry of CuBr4 changed significantly. The 1H and 13C spin–lattice relaxation times (T1ρ) showed very similar molecular motions according to the Bloembergen–Purcell–Pound theory at low temperatures; however, the 1H T1ρ values representing energy transfer were about 10 times lesser than those of 13C T1ρ. Finally, the 1H and 13C T1ρ values of [NH3(CH2)3NH3]MeBr4 (Me = Cu, Zn, and Cd) were compared with those reported previously. 1H T1ρ was affected by the paramagnetic ion of the anion, while 13C T1ρ was affected by the MeBr4 structure of the anion; 13C T1ρ values in Me = Cu and Cd with the octahedral MeBr6 structure had longer values than those in Me = Zn with the tetrahedral MeBr4 structure. We believe that these detailed insights on the physical properties will play a crucial role in the development of eco-friendly hybrid perovskite solar cells.

Zn2+ and Cu2+ doping of one-dimensional lead-free hybrid perovskite ABX3 for white light emission and green solar cell applications

The one-dimensional ABX3 hybrid perovskite (A=(CH3)2NH2=DMA, B=Cd and X=Cl) was synthesized and structurally characterized. The optical analysis showed that the material has a direct band-gap nature with a gap energy of 5.36 eV. The obtained compound exhibited a “cold” white-light emission under an excitation wavelength of 240 nm with a color-rendering index up to 92 and a correlated color temperature (CCT) of 7582 K. The doping of the crystal with Cu2+ ions decreased the gap energy toward 2.51 eV. The partial substitution of the Cd atoms with Cu atoms decreased the intensity of the emitted white-light under 240 nm and led to a “cold” white-light emission with a CCT of 7117 K. The doping of the material with Zn2+ yielded a blue-shift and the emitted light revealed a CCT of 11,028 K. On the other hand, by incorporating Cu2+ions into the B site a broad absorption band is observed in the visible region resulting from the d-d transitions around the copper atoms which makes the material a good visible-light absorber. Hence, the Cu doped compound could be suitable for both white-light emission and photovoltaic solar cells.

Realization of In-Plane Polarized Light Detection Based on Bulk Photovoltaic Effect in A Polar Van Der Waals Crystal.

2D van der Waals materials are widely explored for in-plane polarized light detection owing to their distinctive in-plane anisotropic feature. However, most of these polarized light-sensitive devices root in their low symmetry of in-plane structure and work depending on external power sources, which greatly impedes the simplification of integrated devices and sustainable development. Bulk photovoltaic effect (BPVE), which separates photoexcited carriers via built-in electric field without an external power source and shows an angle-dependence on light polarization, is promising for self-powered polarized light detection to break through the restriction of in-plane anisotropy. Herein, a 2D lead-free van der Waals perovskite (Cl-PMA)2 CsAgBiBr7 (1, Cl-PMA = 4-Chlorobenzylamine) is successfully designed through the dimension reduction strategy. 1 exhibits BPVE with an open-circuited photovoltage up to ≈0.5V. Driven by the BPVE, self-powered in-plane polarized light detection with a large polarization ratio of 1.3 is obtained for 1. As far as it is known, the first in-plane polarized light detection in hybrid perovskites based on BPVE is realized here. This work highlights the strategy of designing lead-free hybrid perovskite with BPVE and opens an avenue for exploiting in-plane highly sensitive polarized light detection in 2D van der Waals materials.