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A research hotspot for the last decade, organometal‐halide perovskites are now showing their promise in numerous optoelectronic devices. With power conversion efficiency (PCE) greater than 25%, perovskite solar cells (PSCs) are approaching the status of popular monocrystalline silicon–based solar cells (SCs). However, the presence of a bioaccumulative lead (Pb) in these perovskite compounds hinders their scalability and commercialization. The endeavor on nontoxic alternatives has triggered a new field of perovskites where Pb has been successfully eliminated. Preliminary studies of photovoltaic (PV) devices based on Pb‐free perovskites have shown some promise; however, they failed to exhibit comparable performance and compositional stability. Therefore, to exploit together the advantages of high efficiency and lesser toxicity, combinations of Pb alternatives with each other as well as with conventional Pb are required in the perovskite framework to fabricate hybrid perovskites (HPVKs). The first part of this Review briefly discusses all possible Pb substitutes and their limitations in PV devices. Based on the Pb contents, the second part elaborates on the two different types of HPVKs (i.e., nontoxic and less toxic) and their progress in photovoltaics. The Review concludes with an outlook discussing current challenges in the way of HPVKs and prospective opportunities to assess their future progress. [ABSTRACT FROM AUTHOR]

Two-dimensional phenylethylammonium (PEA, C8H9NH3) Bi–Ag double perovskite (PEA)4BiAgX8 (X = Br, I) microplatelets are synthesized for the first time via a facile self-assembly recrystallization method. Absorption spectra of microplatelets exhibit direct bandgaps and different halide compositions show distinct morphologies and bandgap tunability. Field-effect transistors based on a single (PEA)4BiAgBr8 microplatelet display a p-type semiconducting behavior. [ABSTRACT FROM AUTHOR]

Organometal halide perovskites (OMHPs) have shown promising applications in solar cells, light-emitting diodes, and photodetectors. However, besides the toxic lead, the intensive usage of organic solvents during their fabrication could induce severe environmental pollution. Therefore, green-solvent fabrication of OMHPs is highly desirable but extremely challenging. Herein, we report aqueous phase fabrication and conversion of laurionite-type Pb(OH)Br into CH3NH3PbBr3. The prepared CH3NH3PbBr3 crystals show prominently enhanced environmental and thermal stability compared to those prepared in organic phases. To demonstrate the application of the prepared CH3NH3PbBr3, a resistive switching memory device (ReRAM) is fabricated. The ReRAM devices exhibit good bipolar non-volatile characteristics that can remain unchanged for more than 30 days under ambient conditions. We believe that the aqueous phase-based green fabrication process of OMHPs will not only greatly alleviate the environmental pollution during or after their commercialization process, but will also provide a new concept in stabilizing and improving the performance of OMHP-based devices. [ABSTRACT FROM AUTHOR]

Organometal halide perovskites (PVKs) have demonstrated their potential in photovoltaics in terms of higher photovoltaic efficiency, aiming to achieve the Shockly-Quieser limit of a single-junction solar cell. Understanding the photo-optical and structural properties of PVKs is crucial to further improving their photovoltaic efficiency. Defects-free PVKs with a suitable energy bandgap (E BG ∼ 1.34 eV) are desirable to capture most of the solar radiations; however, the E BG of the state-of-the-art PVKs is not the ideal one. Compositional engineering offers E BG tunability but decreases carrier lifetime and increases material instability. The application of hydrostatic pressure is a green route, which initiates structural changes in the PVKs and tunes their E BG , leading to the emergence of interesting material properties, including piezochromism, metallization, photoresponsivity, and structural stability. Therefore, understanding the interplay between pressure-induced electronic and structural changes is crucial. Herein, the pressure-induced modifications in structural and optoelectronic properties are elaborated. Particularly, pressure-induced properties in single crystals, lower-dimensional PVKs, and all-inorganic PVKs are comprehended. Moreover, PVK amorphization and strain-induced properties of various PVK materials are also summarized. The review is concluded with an outlook discussing the challenges associated with the pressure induction on PVK material and our perspective to resolve these issues and future work. [ABSTRACT FROM AUTHOR]

• Dodecylammonium chloride assisted the formation of compact lead-free perovskites films. • The crystallinity and stoichiometric defects of the films are significantly improved. • Enhanced optical absorption, photoluminescence, and extended carrier lifetime is achieved. • Solar cell device exhibited a highest PCE for the solution-processed Cs 3 Bi 2 I 9 -based devices. • Photovoltaic device demonstrated an enhanced environmental stability in the ambient air. Bismuth is considered as one of the most promising candidates to replace Pb in the organo-lead halide perovskite, a classical material for various optoelectronic applications. When utilized in a photovoltaic cell, the performance of the cell drops due to deterioration in the absorber film and the changes in its crystal structures. In this work, a small amount of dodecylammonium chloride, C 12 H 25 NH 3 Cl (DCl) is added into Cs 3 Bi 2 I 9 (CBI), resulting in a pinhole-free high-quality perovskite (PVK) film via a single-step solution processability, also confirmed by FTIR and XPS analyses. Structural, optical, and microscopic analyses showed that the quality, surface features, and crystallinity of the CBI films are significantly improved by adding DCl. The prepared films are successfully demonstrated in a solar cell and exhibited considerably improved photovoltaic (PV) characteristics (V OC by ~47%, J SC by ~33%, FF by 13%, and PCE by 115%) over pure CBI-based devices. Moreover, the PV device retained more than 95% of its initial PCE in the ambient laboratory environment (relative humidity 55±5%). To the best of our knowledge, this is the highest PCE along with extended environmental stability reported for solution processed CBI-based perovskite solar cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dodecylammonium chloride as an additive helps in the ambient fabrication of perovskite films. • Low-temperature hot-casting is realized in the preparation of perovskite films in an ambient environment. • Perovskite films exhibited better crystallinity and bigger grains (<110 µm) • Low-voltage operational ReRAM devices with a high ON/OFF ratio are realized. Fabricating perovskite (PVK) films with large grains and compact grain boundaries via solution processability is demanding for efficient electronic and optoelectronic devices. Hot-casting produces dense PVK films with bigger and adjacent grains; however, involves higher temperatures and an inert atmosphere that increases the fabrication cost. Herein, using dodecylammonium chloride (DCl) as an additive, combined with hot-casting is utilized and compact bi-cation PVK films with grain size > 110 µm are synthesized at lower temperature and ambient air. It is revealed that the films have a dense microstructure with no voids among the grains. Also, the films are highly crystalline with preferentially orientated crystals and showed greater hydrophobicity and an extended carrier lifetime. Finally, the films are employed in a resistive-memory storage device, which demonstrated a high ON/OFF ratio of > 106 and lower power consumption. Such high-quality films prepared at ambient conditions could be useful for the realization of other highly efficient optoelectronic devices. [ABSTRACT FROM AUTHOR]

The band alignments at the interface of ZnO/HC(NH 2 ) 2 PbI 3 (FAPbI 3 ) heterojunction were measured by X-ray photoelectron spectroscopy. Core levels of Pb 5d and Zn 3d were utilized to align the valence-band offset (VBO). The VBO was determined to be 1.86 ± 0.30 eV, and the conduction-band offset (CBO) was concluded to be 0.05 ± 0.30 eV, manifesting that the ZnO/FAPbI 3 heterojunction has a type-I band alignment. The data of the band alignment of ZnO/FAPbI 3 heterojunction may benefit the design and development of novel perovskite solar cells (PSCs). [ABSTRACT FROM AUTHOR]

• All-inorganic zinc halide perovskite variant Cs2ZnCl4 crystals with Sb3+ doping are synthesized via hydrothermal method • Crystals exhibit self-trapped exciton emission, which is attributed to the transition from 3P1 to 1S0 states of Sb3+. • Temperature-dependent and time-resolved photoluminescence reveal the emission evolution with temperature. • Calculations reveal the influences of Sb3+ doping in Cs2ZnCl4, including bandgap reduction and band edge localization. Halide lead perovskites are considered as one of the most promising optoelectronic materials in decades, but the toxicity and bio-accumulation of lead retard the commercialization. Therefore, seeking suitable lead-free perovskites and their variants are of vital importance. In this work, all-inorganic zinc halide perovskite variant Cs 2 ZnCl 4 crystals with Sb3+ doping are synthesized via hydrothermal method. Transparent millimeter-sized crystals exhibit bright red photoluminescence (PL) under room temperature (RT) on account of self-trapped exciton (STE) emission of Sb3+, from 3P 1 to 1S 0 states. Temperature-dependent PL and time-resolved PL exhibit bimodality and intensity variations, revealing that Jahn-Teller effect of 3P 1 state results two energy minima, and thermal activation may contribute to the spectrum change. Further, DFT calculations are carried out and the influences of Sb3+ doping are revealed. A bandgap reduction is achieved via doping, and the band edges are localized at Sb3+. A combination of experimental and theoretical studies demonstrates well that the soft lattice structure and the 5s2 lone pairs of Sb are vital for the STE emission. [ABSTRACT FROM AUTHOR]