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Hybrid bimetallic halides with two different optical activities have exhibited excellent optical properties, which demonstrates great potential in the optoelectronic fields. To develop hybrid cuprous-lead bimetallic halides with unique non-centrosymmetric structures, we introduced the chiral cations R/S-2-C5H14N22+(C5H14N22+= methylpiperazinium) into inorganic frameworks containing two different heterometallic cuprous and lead cations, respectively, and successfully obtained the novel chiral hybrid bimetallic halides of (R/S-2-C5H14N2)3Cu2Pb2I12single crystals by the hydrothermal method. Bimetallic anionic [Cu2Pb2I12]6–framework structures were constructed from two different [PbI6]4–and two different [CuI4]3–twisted polyhedra, and band gap calculations were demonstrated. Most importantly, chiral crystal structures of (R/S-2-C5H14N2)3Cu2Pb2I12were confirmed by circular dichroism (CD), and their anisotropy factor (gCD) values were –5.98 × 10–5and +5.79 × 10–5, respectively. Besides, significant second harmonic generation of (R/S-2-C5H14N2)3Cu2Pb2I12single crystals was also exhibited through the coupling of chiral organic cations and inorganic anionic [Cu2Pb2I12]6–frameworks. This work not only provides guidance for understanding the structure–property relationship of novel chiral hybrid bimetallic halides, but also extends the further optoelectronic applications of these hybrid halide systems.

Mn(II)-based hybrid halides have attracted great attention from the optoelectronic fields due to their nontoxicity, special luminescent properties, and structural diversity. Here, two novel organic–inorganic hybrid Mn(II)-based halide single crystals (1-mpip)MnCl4·3H2O and (1-mpip)2MnCl6(1-mpip = 1-methylpiperazinium, C5H14N2+) were grown by a slow evaporation method in ambient atmosphere. Interestingly, (1-mpip)2MnCl6single crystals exhibit the green emission with a PL peak at 522 nm and photoluminescence quantum yields (PLQYs) of ≈5.4%, whereas (1-mpip)MnCl4·3H2O single crystals exhibit no emission characteristics. More importantly, there exists a thermal-induced phase transformation from (1-mpip)MnCl4·3H2O to emissive (1-mpip)2MnCl6at 372 K. Moreover, a reversible luminescent conversion between (1-mpip)MnCl4·3H2O and (1-mpip)2MnCl6was simply achieved when heated to 383 K and placed in a humid environment or sprayed with water. This work not only deepens the understanding of the thermal-induced phase transformation and humidity-sensitive luminescent conversion of hybrid Mn(II)-based halides, but also provides a guidance for thermal and humidity sensing and anticounterfeiting applications of these hybrid materials.

Introducing electronegative species into organic constituents was considered to be one effective strategy for adjusting crystal symmetry and designing new nonlinear optical (NLO) materials. By substitution of C4 in piperidine (C5H11N) with electronegative oxygen, organic morpholine (C4H9NO) was easily obtained. Therefore, to design NLO crystals, we focused on combinations of stereochemically active lone-pair (SCALP) cation (Pb2+)-based chloride and bromide with morpholine molecules. In this work, two lead halide hybrid perovskite (C4H10NO)PbX3(X = Cl, Br, abbreviated as MPbCl3and MPbBr3, respectively) single crystals with moderate nonlinear optical properties were synthesized by a slow evaporation method. The two title crystals belong to orthorhombic space group P212121with one-dimensional (1D) chainlike perovskite structures. Theoretical calculations revealed that the second harmonic generation (SHG) responses mainly originate from distorted {PbX6} octahedrons of the inorganic framework. Remarkably, moderate phase-matching SHG effects of about 0.70 and 0.81 times KH2PO4, large birefringences of 0.098 and 0.111 at 1064 nm, and large laser damage thresholds (LDTs) of 19.94 and 46.82 MW/cm2were estimated for MPbCl3and MPbBr3, respectively. This work provides a novel strategy for new purpose-designed hybrid NLO crystals by adjustment and modulation of chemical modification.

Acentric materials with bulk photovoltaic effect (BPVE) have recently emerged as a class of promising optoelectronic materials due to broken inversion symmetry. In this review, we mainly aim to provide a comprehensive understanding of acentric single crystals for BPVE-based optoelectronic applications. An overview of research background and recent progress of the acentric materials with BPVE is described. Moreover, the characteristics of BPVE and BPVE-based optoelectronic device applications are illustrated in detail. Finally, possible future research directions and challenges of the acentric single crystals and their optoelectronic devices with BPVE characteristics are proposed with our viewpoints in the emerging optoelectronic field.

To design nonlinear optical (NLO) materials, we focused on combinations of d10metal cation (Cd2+)-based chloride and morpholine molecules to form organic–inorganic hybrids. The O of morpholine containing lone-pair electrons can be integrated with Cd2+by a ligand-to-metal charge transfer (LMCT) strategy to build acentric structures benefiting from the second-order Jahn–Teller effect. Introduction of the high-electronegativity chlorine can make polyhedrons of acentric crystals more distorted and conducive to a strong second harmonic generation (SHG) response. Therefore, (Morpholinium)2Cd2Cl6crystals were constructed and synthesized by a solvent evaporation method. (Morpholinium)2Cd2Cl6belongs to the orthorhombic P212121space group and shows a one-dimensional (1D) structure with distorted [CdCl6] and [CdCl4O2] octahedrons. The short cutoff edge of (Morpholinium)2Cd2Cl6was determined to be about 230 nm. The SHG response of (Morpholinium)2Cd2Cl6exhibited an intensity of approximately 0.73 × KDP as estimated by the powder second harmonic generation technique. Furthermore, related theoretical calculations were performed to study the relationship of the band structure, refractive anisotropy, electronic state, and nonlinear optical response. Besides, (Morpholinium)2Cd2Cl6showed relatively good thermal stability. This work can serve as a guide for the design and synthesis of new large NLO hybrid crystals with d10transition metals.

Lead (Pb)-free halide hybrid materials have received a great deal of attention because of their potential in optoelectronic applications. However, heteroatom-based amine lead-free tin halide hybrid single crystals have not been well investigated yet. Detailed synthetic processes, growth, crystal structures, and stability of (ACH2CH2NH3)2SnBr6(A = OH or SH) and (BCH2CH2NH3)2SnI4(B = I or SH) single crystals were investigated. Interestingly, (IH3NCH2CH2SSCH2CH2NH3)2HPO3exhibited orange-red photoluminescence (PL) at about 620 nm with an average PL lifetime of about 912 ns. (HSCH2CH2NH3)2SnI4single crystals exhibited a PL peak at 620 nm with an average PL lifetime of about 0.607 ns. More importantly, (HSCH2CH2NH3)2SnI4single crystals exhibited reversible red–black color transformations when exposed to a H3PO2solution and an ambient atmosphere, which was attributed to oxidation from Sn2+to Sn4+, rather than from I–to I3–(I2). The intriguing characteristics should provide guidance for further optoelectronic applications of these Pb-free halide hybrid materials.

Chiral halide perovskites have recently emerged as a class of potential optoelectronic materials. In this review, we mainly aim to provide a comprehensive understanding of chiral halide perovskite crystals for optoelectronic applications. An overview of the research background and advancement of chiral halide perovskites is described. Crystal structure, synthesis, and growth methods of chiral halide perovskite single crystals are demonstrated. Moreover, the characteristic properties and optoelectronic applications of chiral halide perovskites are systematically illustrated. Finally, future research opportunities and challenges of chiral halide perovskite single crystals and related devices are provided, concluding with our perspective on the burgeoning optoelectronic field.

To study stability issues of three-dimensional perovskites, there is a strategy to introduce the thiocyanate ion (SCN–) into CH3NH3PbI3(MAPbI3) to solve these problems. Here, we report the bulk growth of layered perovskite MA2Pb(SCN)2I2single crystals by different growth methods in an ambient atmosphere. We also investigate the structural determination and refinements, band gap, and photoluminescence of MA2Pb(SCN)2I2single crystals. More importantly, the phase transition and stability of MA2Pb(SCN)2I2are systematically demonstrated. MA2Pb(SCN)2I2undergo the reversible single-crystal to single-crystal phase transition in the orthorhombic systems from the space group Pmmn(no. 59) to the space group Pmn21(no. 31) at low temperature. Moreover, the temperature-dependent recovery behaviors of MA2Pb(SCN)2I2single crystals, powders, and thin films at high temperature are studied in detail. Besides, the moisture stability of MA2Pb(SCN)2I2is described when exposed to moisture condition by the experiment and theoretical calculations. It would be interesting to not only conduct a comprehensive study on the crystal structures and the phase transition processes of layered perovskites but also provide guidance for further optoelectronic applications of these perovskite materials.

Tin-based perovskite solar cells (PSCs), with more consummate optical band gaps, lower exciton-binding energies, and higher charge-carrier mobility, have not attracted tremendous research efforts compared with the lead-based ones that have a record power conversion efficiency (PCE) of 24.2%. The major challenges for Sn-based research are significantly low open-circuit voltage, poor reproducibility, and environmental instability. It has been identified that the oxidation processes take place during the preparation of precursor solutions and fabrication of films, due to the low redox potential of the stannous absorption layer. Herein, we propose two strategies of crystal-resolving and recrystallization technology to reduce the oxidation process. As a result, PCEs of 8.9% (active area of 0.04 cm2) and 5.5% (active area = 1.01 cm2) are attained using the inverted p-i-n structure, which will lead to a revival of lead-free PSC research.

Chiral lead halide perovskites (chiral LHPs) have emerged as one of the best candidates for opto-spintronics due to their large spin–orbit coupling (SOC) and unique chirality-induced spin selectivity (CISS) even in the absence of a magnetic field. Here, we report the impact of halide composition on circular dichroism (CD) and magneto-photoluminescence (PL) effects of chiral 2D LHPs (R/S-MBA)2PbBrxI4–x(MBA = C6H5CH2(CH3)NH3). By tuning the mixing ratio of Br/I halide anions, we find that (R/S-MBA)2PbBrxI4–xthin films exhibit tunable and wide wavelength range CD signals. Simultaneously, the main CD signals near the exciton absorption band gradually blue shift until they disappear. Moreover, the halogen-dependent negative magneto-PL effects of (R/S-MBA)2PbBrxI4–xthin films excited by left/right circularly polarized light can be detected at room temperature. We demonstrated that the halide composition can effectively modulate exciton splitting and chirality transfer in (R/S-MBA)2PbBrxI4–xowing to the chirality-induced SOC and crystalline structure transition, which lead to the adjustable CD signals. The interplay of Rashba-type band spin splitting and spin mixing among bright triplet exciton states is responsible for the halogen-dependent magneto-PL effect of chiral 2D LHPs. This study enables chiral 2D LHPs with CISS to be a new class of promising opto-spintronics materials for exploring high-performance spin-light-emitting diodes by halide engineering.

Organic–inorganic hybrid metal halides have unique optical and electronic properties, which are advantageous in the study of nonlinear optical materials. To investigate the effect of stereoactive lone pair electrons and the induction of organic cations on the structure of hybrid antimony(III) halides on nonlinear optics, we synthesize two noncentrosymmetric hybrid antimony(III)-based halide single crystals (TMA)3Sb2X9(TMA = NH(CH3)3+, X = Cl, Br) by a room-temperature slow evaporation method, and their single-crystal structures, phase transition, X-ray photoelectron spectroscopy, and energy-band structure calculations are studied. More importantly, second-harmonic generation results of (TMA)3Sb2X9(X = Cl, Br) are about 0.7 and 0.8 × KH2PO4(KDP), respectively. Interestingly, (TMA)3Sb2Cl9single crystals undergo a reversible structural transition from Pc(No. 7) at room temperature to P21/c(No. 14) at 400 K, while the (TMA)3Sb2Br9single crystals belong to the noncentrosymmetric space group R3c (No. 161), which clarifies the previous results. This work not only deepens the understanding of the role in lone pair electrons and organic cations in the structural induction in antimony-based halide perovskite materials but also provides guidance for subsequent nonlinear optical explorations.

In order to reveal the integrated effect of inorganic lattice structure disturbances and chiral ligands on the structure of tin halide hybrid materials, we show the synthesis, crystal growth, dissolution recrystallization structural transformation (DRST), optical properties, energy band structure, and nonlinear optical properties of a class of chiral tin bromide R/S-2-mpip[SnBr3]Br (2-mpip is 2-methylpiperazinium) and R/S-2-mpipSnBr6for the first time. The formation of R/S-2-mpipSnBr6in solution was interestingly caused by irreversible DRST of R/S-2-mpip[SnBr3]Br. The second-harmonic generation response of the new phase R-2-mpipSnBr6is significantly enhanced compared to that of the initial phase R-2-mpip[SnBr3]Br. These structural transformations of chiral tin bromides reflect, to some extent, the DRST commonality of the tin halide family induced by oxidation and serve as a starting point for investigating the structural chirality and asymmetry of chiral metal hybrid halides.

Achieving an excellent electron transport layer is significant for high-performance perovskite solar cells. A TiO2compact film is extensively applied as an electron transport layer. However, some limiting issues, such as unfavorable band offset, unsatisfactory electrical conductivity, low electron mobility, and high-density defects, remain in the TiO2electron transport layer. In this work, yttrium (Y) is proposed as a dopant in the TiO2electron transport layer. It is revealed that the incorporation of Y promotes the Fermi energy level of TiO2shift upward, bringing about more favorable energy-level alignment for the transport of photogenerated carriers. In addition, the device assembled with a Y-TiO2electron transport layer exhibits an increased built-in potential, suggesting a more powerful driving force for charge separation and transport. Eventually, the triple-cation perovskite solar cell equipped with a Y-TiO2electron transport layer acquires an efficiency of 20.09%. It is superior to that of the TiO2-based device (17.28%). The results indicate that Y-ion doping is a promising method to fabricate highly efficient perovskite solar cells.

Organic–inorganic hybrid Pb-halide perovskites have attracted tremendous interest due to their potential application in photovoltaic and optoelectronic fields. However, the toxicity and poor stability of Pb-halide perovskites have become key bottlenecks toward their future commercialization and industrialization. Therefore, in this work, two novel hybrid lead-free perovskite nonlinear optical (NLO) crystals (2-AMP)2BiX7·H2O (X = Cl, Br) with high stability were successfully synthesized. Both the crystals belong to the orthorhombic P212121space group, displaying a zero-dimensional perovskite structure. The thermal, environmental, and solvent atmospheric stabilities were comprehensively investigated, with high thermal stability up to 170 °C and high environmental and high solvent atmospheric stability observed for (2-AMP)2BiBr7·H2O. First-principles calculations were carried out to study the relationship of the structure and properties. A large birefringence of 0.1368@1064 nm was determined for (2-AMP)2BiBr7·H2O, which was derived from the strong aeolotropic conjugated π-electron distribution of planar 2-aminomethylpyridium. A second-harmonic generation (SHG) effect that was 0.25 and 0.32 times that of KH2PO4(KDP) was measured for (2-AMP)2BiCl7·H2O and (2-AMP)2BiBr7·H2O, respectively, and the stronger SHG response of bromide was attributed to the larger distortions of {BiBr6} octahedrons. This work may offer new guidance for exploration of low toxicity and high stability of perovskite NLO materials.

High efficiency and long-term stability are vital for further development of perovskite solar cells (PSCs). PSCs based on cesium lead halide perovskites exhibit better stability but lower power conversion efficiencies (PCEs), compared with organic-inorganic hybrid perovskites. Lower PCE is likely associated with trap defects, overgrowth of partial crystals and irreversible phase transition in the films. Here we introduce a strategy to fabricate high-efficiency CsPbBr3-based PSCs by controlling the ratio of CsBr and PbBr2to form the perovskite derivative phases (CsPb2Br5/Cs4PbBr6) via a vapor growth method. Following post-annealing, the perovskite derivative phases as nucleation sites transform to the pure CsPbBr3phase accompanied by crystal rearrangements and retard rapid recrystallization of perovskite grains. This growth procedure induced by phase transition not only makes the grain size of perovskite films more uniform, but also lowers the surface potential barrier that existsbetween the crystals and grain boundaries. Owing to the improved film quality, a PCE of 10.91% was achieved for n-i-p structured PSCs with silver electrodes, and a PCE of 9.86% for hole-transport-layer-free devices with carbon electrodes. Moreover, the carbon electrode-based devices exhibited excellent long-term stability and retained 80% of the initial efficiency in ambient air for more than 2000 h without any encapsulation.