Chiroptical Devices Using Pb(II)/Bi(III)/Te(IV)-Based One-Dimensional Helical Perovskites

One-dimensional (1D) anisotropic crystal structures with broken spatial inversion symmetry exhibit unique spin-induced physical phenomena and have garnered significant attention. This study focuses on 1D helical lead halide perovskites incorporating organic chiral molecules, demonstrating the controlled generation of helical and polar structures for circularly polarized light (CPL) detection [1] and bulk photovoltaic effects [2]. The 1D structure consists of face-sharing (PbI6)4- octahedral chains, with the helicity of the chains strongly influenced by chiral cations with aromatic structures. In this work, R-(+)- and S-(-)-1-(1-naphtyl)ethylamine (R- and S-NEA+) were selected as chiral cations in the 1D perovskite. The large π-conjugated naphthalene skeleton in NEA+ interacts with neighboring molecules within the crystal, significantly affecting the helicity of the (PbI6)4- octahedral chains. The resulting helical 1D perovskites with NEA+ exhibit the largest circular dichroism (CD) signals ever reported in chiral perovskites with 1D or 2D structures. First-principles calculations revealed the indirect transition nature of the helical 1D structure, leading to unique electronic properties that contribute to its giant CD properties. Photodetectors fabricated using thin films of the helical 1D perovskite demonstrate extremely sensitive CPL detection, achieving a high polarization extinction ratio (R L/R R = 25.4). The high photoconductivity and strong polarization exciton ratio under CPL irradiation are attributed to the polarized electronic spin generated by selective CPL absorption and the large spin-orbit coupling of Pb and I, which are consistent with spin-dependent optical selection rules.The crystal structure acting as a CPL detector adopts a chiral but non-polar P212121 space group, which can be converted into a chiral and polar C2 space group through a thermally controlled crystallization process. Notably, the 1D helical perovskite crystals with a chiral and polar structure exhibit an anomalous bulk photovoltaic effect, characterized by zero-bias photocurrent generation and open-circuit voltages of up to 15 V, five times larger than the bandgap. The unique polarization direction along the helical axis suggests potential ferroelectric properties. This study highlights how the polar and helical arrangement induced by organic chiral molecules enhances both chiral optical and polar properties, offering promising applications in photovoltaics, photodetection, and spintronics.Reference：[1] A. Ishii, T. Miyasaka, Science Adv., 2020, 6, eabd3274. [2] A. Ishii, et al., in Review. Figure 1

Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics

Probing pi-conjugated polymers with circularly polarized light

Triplet Sensitization by Lead Halide Perovskite Thin Films for Efficient Solid-State Photon Upconversion at Subsolar Fluxes

The homochirality of life remains one of the most enigmatic issues in the study of the origin of life. A proposed mechanism for symmetry breaking involves irradiation by circularly polarized light (CPL). To investigate the photoreaction of amino acids under CPL irradiation, a vacuum ultraviolet (VUV) CPL irradiation system was developed at the synchrotron light source UVSOR-III. Hydrogen Lyman-α CPL (121.6 nm) is considered a potential asymmetric source in space. Therefore, racemic alanine film samples were irradiated with Lyman-α CPL to explore the photoreaction of biomolecules. Circular dichroism (CD) spectra measurements revealed that irradiation with right- (left-) handed CPL induced a positive (negative) anisotropy factor g in the wavelength range of 180-240 nm. However, the spectra differed from those of enantiopure alanine, exhibiting broad wavelength ranges and no sign change. Liquid chromatography-mass spectrometry (LC-MS) measurements indicate formation of larger molecules, such as oligomeric alanine adducts or modified oligomers after the Lyman-α CPL irradiation. Additionally, CPL irradiation considerably changes the microstructure of the alanine film surface, leading to the formation of circular network aggregates on the scale of 100 nm. The morphology changes in the alanine film and/or the formation of the larger molecules could be possible causes of the modified anisotropy factor spectra compared to those of enantiopure alanine. These findings highlight the need for further research on the photoreaction of biomolecules in solid states under VUV CPL irradiation, particularly in the photoionization energy range, to validate the cosmic scenario of homochirality.

Due to their high efficiency and low cost, organic-inorganic hybrid perovskite solar cells are attracting growing interest recently. For the most commonly studied perovskite CH3NH3PbI3, optimization of the morphology and crystallinity of CH3NH3PbI3 thin films can greatly improve the efficiency of perovskite solar cells. A homogenous and uniform perovskite film can prevent direct contact between the hole transport layer and the electron transport layer, and thus can significantly reduce charge recombination. And the high crystallinity perovskite film facilitates fast charge transportation and injection. Various studies have proved that solvent has a critical influence on both the morphology and the crystallinity of perovskite thin films. In this work, we thoroughly studied the influence of the normally used N, N-Dimethylformamide (DMF) and r-butyrolactone (GBL) solvents on perovskite morphology, crystallinity, as well as the solar cells efficiency. When using DMF as the solvent, the efficiency is only 2.8%, while the efficiency of the cell obtained based on GBL can reach 10.1%. SEM and HRTEM are employed to study the morphology and crystallinity of these two kinds of perovskite films. The perovskite film prepared using solvent DMF shows a rough capping layer consisting of strip-like perovskite crystals, and the filling of meso-TiO2 is poor. Compared with DMF, the GBL perovskite film shows a better capping layer structure consisting of large perovskite domains, and the filling of meso-TiO2 is improved as well. This great difference in capping layer morphology and meso-TiO2 filling is one reason for the different performance. Besides morphology, different defect concentrations in these two kinds of perovskite films are another crucial issue. By Combined XRD and UV techniques, the mechanisms how perovskite precipitats from DMF and GBL solutions can be disclosed. In DMF, because of its low spoiling point of 153 ℃, most of DMF solvent volatilize by spin-coating, and an intermediate MOF structure of PbI2: MAI: xDMF is formed. During thermal annealing, the unstable MOF structure breaks down and a large amount of dislocations form in perovskite films, which highly restrict the charge transport. However, the spoil point of GBL (206 ℃) is higher than that of DMF, which makes it hard to be fully volatilized by spin-coating. During the following thermal treatment, the solubility of perovskite is lowered with increasing temperature. So perovskite crystallites precipitate from the GBL first and then gradually grow up with the volatilization of the excess solvent. We finally find that coordination between the solvent and the PbI2 plays a big role on the morphology and the crystallinity of the solution-processed perovskite film, and this is responsible for the difference of the device performance.

Influence of Charge Transport Layers on Capacitance Measured in Halide Perovskite Solar Cells

Large-area perovskite solar cells

Small grains as recombination hot spots in perovskite solar cells

At present, there are many reports on the preparation of large area CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> perovskite solar cells based on ink-jet printing. These researches focus mainly on the ink-jet printing and electrode printing of perovskite active layer films. The hole transport layer, electron transport layer and other modified layers in the cell structure are still completed by spin coating or coating. In this work, we successfully realize large area CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> perovskite solar cells based on full ink-jet printing, including pen/Ag NWs bottom electrode, agnws top electrode, PEDOT: PSS hole transport layer, etc. It is found that the full inkjet printing can greatly reduce the material cost and simplify the production process, and obtain PC<sub>61</sub>BM layer, PEDOT: PSS layer, PEI layer and CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> perovskite thin film with high density and good uniformity. On this basis, we prepare the CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> perovskite solar cells with areas of 60, 80 and 100 cm<sup>2</sup>, respectively. The results show that when the concentration of perovskite ink is 1 mol/L, the printing speed is 30 mm/s and the substrate temperature is 50 ℃, the surface of perovskite film is smooth and the grain size is in a range of 500–600 nm. The surface roughness of the film is only 10 nm, so high-quality perovskite film can be obtained. The power conversion efficiency of the perovskite solar cell with an effective area of 60 cm<sup>2</sup> is as high as 14.25% (<i>V</i><sub>OC</sub> = 1.03 V, <i>J</i><sub>SC</sub> = 19.21 mA/cm<sup>2</sup>, FF = 72%), which is the highest efficiency of perovskite solar cell prepared by full ink-jet printing method reported so far. In addition, when the device is placed in the air for 12 months without packaging, the photoelectric conversion efficiency is reduced to 80% of the initial value. However, the photoelectric conversion efficiency of FTPU package is reduced only by 5%, demonstrating good device stability.

The ability to photoinduce enantiomeric excess from the chirality of circularly polarized light (CPL) is pertinent to the study of the origin of homochirality in biomolecules. Such CPL-induced reactions, including both chirality generation and formation of partial enantiomeric imbalance, from nonchiral starting compounds have been known, however, only for the conversion of diarylolefins into chiral helicenes. In this study we synthesized three different prochiral molecules, each featuring a pair of photoisomerizable phenylazo moieties arranged symmetrically upon the phenyl rings of an sp3-hybridized carbon atom (1), the phenyl rings of [2.2]paracyclophane (2), and the ortho positions of a phenyl ring bearing a naphthyl unit (3), and then investigated the possibility of photoinducing enantiomeric excess under CPL. Irradiation of 1-3 with light induced E ↔ Z photoisomerizations of their azobenzene moieties, giving mixtures of their EE, EZ, and ZZ isomers in the photostationary state (PSS). Among these regioisomers, the EZ forms are chiral and existed as racemic mixtures of R and S stereoisomers. Upon CPL irradiation of 3, circular dichroism (CD) revealed enantiomeric enrichment of one of the EZ stereoisomers; furthermore, irradiation with r- or l-CPL gave CD signals opposite in sign, but with equal intensity, in the PSS. In contrast, 1 and 2 did not give any detectable induced CD upon CPL irradiation. These experimental results can be explained by considering the different Kuhn anisotropy factors (g) of the (R)-EZ and (S)-EZ stereoisomers of 1-3, assuming that the origin of the enantiomeric excess is the enantio-differentiating photoisomerization from EZ stereoisomers to nonchiral EE or ZZ regioisomers by r- or l-CPL. In short, we demonstrate the simultaneous induction of chirality and enantiomeric excess from a prochiral azobenzene dimer via a chiral regioisomer formed in situ upon CPL irradiation.

To achieve fabrication and cost competitiveness in organic optoelectronic devices that include organic solar cells (OSCs) and organic light-emitting diodes (OLEDs), it is desirable to have one type of material that can simultaneously function as both the electron and hole transport layers (ETLs and HTLs) of the organic devices in all device architectures (i.e., normal and inverted architectures). We address this issue by proposing and demonstrating Cs-intercalated metal oxides (with various Cs mole ratios) as both the ETL and HTL of an organic optoelectronic device with normal and inverted device architectures. Our results demonstrate that the new approach works well for widely used transition metal oxides of molybdenum oxide (MoOx) and vanadium oxide (V2Ox). Moreover, the Cs-intercalated metal-oxide-based ETL and HTL can be easily formed under the conditions of a room temperature, water-free and solution-based process. These conditions favor practical applications of OSCs and OLEDs. Notably, with the analyses of the Kelvin Probe System, our approach of Cs-intercalated metal oxides with a wide mole ratio range of transition metals (Mo or V)/Cs from 1∶0 to 1∶0.75 can offer significant and continuous work function tuning as large as 1.31 eV for functioning as both an ETL and HTL. Consequently, our method of intercalated metal oxides can contribute to the emerging large-scale and low-cost organic optoelectronic devices. Caesium-intercalated metal oxides can act as both hole and electron transport layers in organic optoelectronic devices, shown by a team in China. The use of a single material for both layers will reduce the cost of fabricating organic solar cells (OSCs) and organic light-emitting diodes (OLEDs). The researchers, who are from the University of Hong Kong and the Chinese Academy of Sciences, use molybdenum and vanadium oxides intercalated with different caesium mole ratios for both hole and electron transport layers; previously, these metal oxides have generally been used for the hole transport layer only. The results reveal that these caesium-intercalated metal oxides provide efficient performance and good adaptability for OSCs and OLEDs with both conventional and inverted device architectures. This approach can simplify the fabrication of OSCs and OLEDs and has great potential for organic optoelectronic devices.

Low-dimensional hybrid organic-inorganic perovskites (HOIPs) containing chiral organic ligands have recently emerged as promising candidates for circularly polarized light (CPL) detection, which can distinguish left- and right-handed CPL directly. However, the increase in responsivity and realization of self-powered CPL photodetector remain a challenge. Meanwhile, there is a trade-off between the photocurrent responsivity and the ability to differentially absorb CPL in detectors based on these low-dimensional perovskites. Herein, we report the CPL photodetector based on chiral quasi-2D perovskite films (S/R-MBA)2MAPb2I7 and propose a crystallization regulation method using dimethyl sulfoxide (DMSO) and methylammonium thiocyanate (MASCN). We found that the photoelectric response capability and circular dichroism (CD) intensities of chiral quasi-2D perovskite can be enhanced simultaneously by the improved crystallinity and surface morphology of chiral films. Meanwhile, the formation of the tetragonal perovskite structure leads to symmetry-breaking distortion of the inorganic frameworks, further enhancing the chirality of the perovskite films. In addition, the distribution of n-phase can be tuned by DMSO and MASCN to form graded band alignment, effectively promoting the charge transfer in perovskite. As a result, a self-powered CPL photodetector with a high responsivity of 0.82 A/W and an anisotropy factor of 0.09 at 0 V bias is obtained. To the best of our knowledge, it is the first attempt to enhance the CD characteristics of chiral quasi-2D perovskite films. We believe our work further advances the research of low-dimensional chiral perovskite films in the field of CPL detection.

ABSTRACTPerformance of a perovskite based solar cell is highly determined by the crystalline qualities of the perovskite thin film sandwiched between an electron and a hole transport layer, such as grain size and uniformity of the film. Here, we demonstrated a new hybrid physical-chemical vapor deposition (HPCVD) technique to synthesis high quality perovskite films. First, a PbI2 precursor film was spin-coated on a mesoporous TiO2 (m-TiO2)/compact TiO2 (c-TiO2)/FTO substrate in ambient environment. Then, purified CH3NH3I crystal material was evaporated and the vapor reacted with the PbI2 precursor film in a vacuum pressure/temperature accurately controlled quartz tube furnace. In this technique, high vacuum (2mTorr) and low temperature (100°C) were applied to decrease perovskite film growth rate and reduce perovskite film defects. After vapor reaction, the perovskite film was annealed at 100°C for 10min in 20mTorr vacuum to recrystallize and remove CH3NH3I residue in order to further improve crystal quality of the thin film. Crystal quality of this perovskite thin film was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). SEM and AFM results illustrate perovskite thin films synthesized by this technique have larger grain sizes and more uniformity (RMS 11.6nm/Ra 9.3nm) superior to most existing methods. Strong peaks shown in the XRD chart at 14.18°, 28.52°, 31.96°, which were assigned to (110), (220), (330) miller indices of CH3NH3PbI3 perovskite crystal, indicate the complete reaction between CH3NH3I vapor and PbI2 precursor layer. High power conversion efficiency (PCE) up to 12.3% and stable efficiencies under four hours illumination of AM1.5 standard were achieved by these solar cells. This vacuum/vapor based technique is compatible with conventional semiconductor fabrication techniques and high quality perovskite film could be achieved through delicate process control. Eventually, perovskite based solar cells could be mass produced in low cost for large scale applications by this novel technique.

Two-dimensional Bi2OS2 doping improves the performance and stability of perovskite solar cells