Blade-Coating (100)-Oriented α-FAPbI3 Perovskite Films via Crystal Surface Energy Regulation for Efficient and Stable Inverted Perovskite Photovoltaics.

Photoactive formamidinium lead triiodide (α-FAPbI3) perovskite has dominated the prevailing high-performance perovskite solar cells (PSCs), normally for those spin-coated, conventional n-i-p structured devices. Unfortunately, α-FAPbI3 has not been made full use of its advantages in inverted p-i-n structured PSCs fabricated via blade-coating techniques owing to uncontrollable crystallization kinetics and complicated phase evolution of FAPbI3 perovskites. Herein, a customized crystal surface energy regulation strategy has been innovatively developed by incorporating 0.5 mol% of N-aminoethylpiperazine hydroiodide (NAPI) additive into α-FAPbI3 crystal-derived perovskite ink, which enabled the formation of phase-pure, highly-oriented α-FAPbI3 films. We deciphered the phase transformation mechanisms and crystallization kinetics of blade-coated α-FAPbI3 perovskite films via combining a series of in-situ characterizations. Interestingly, the strong chemical interactions between the NAPI and inorganic Pb-I framework help to reduce the surface energy of (100) crystal plane by 42%, retard the crystallization rate and lower the formation energy of α-FAPbI3. The resultant blade-coated inverted PSCs based on (100)-oriented α-FAPbI3 perovskite films realized promising efficiencies up to 24.16% (~26.5% higher than that of the randomly-oriented counterparts), accompanied by improved operational stability. This result represented one of the best performances reported to date for FAPbI3-based inverted PSCs fabricated via scalable deposition methods.

Synergic Electron and Defect Compensation Minimizes Voltage Loss in Lead-Free Perovskite Solar Cells.

Sn perovskite solar cells have been regarded as one of the most promising alternatives to the Pb-based counterparts due to their low toxicity and excellent optoelectronic properties. However, the Sn perovskites are notorious to feature heavy p-doping characteristics and possess abundant vacancy defects, which result in under-optimized interfacial energy level alignment and severe nonradiative recombination. Here, we reported a synergic "electron and defect compensation" strategy to simultaneously modulate the electronic structures and defect profiles of Sn perovskites via incorporating a traced amount (0.1 mol %) of heterovalent metal halide salts. Consequently, the doping level of modified Sn perovskites was altered from heavy p-type to weak p-type (i.e. up-shifting the Fermi level by ∼0.12 eV) that determinately reducing the barrier of interfacial charge extraction and effectively suppressing the charge recombination loss throughout the bulk perovskite film and at relevant interfaces. Pioneeringly, the resultant device modified with electron and defect compensation realized a champion efficiency of 14.02 %, which is ∼46 % higher than that of control device (9.56 %). Notably, a record-high photovoltage of 1.013 V was attained, corresponding to the lowest voltage deficit of 0.38 eV reported to date, and narrowing the gap with Pb-based analogues (∼0.30 V).

Near-Stoichiometric and Homogenized Perovskite Films for Solar Cells with Minimized Performance Variation.

Mixed-cation, small band-gap perovskites via rationally alloying formamidinium (FA) and methylammonium (MA) together have been widely employed for blade-coated perovskite solar cells with satisfied efficiencies. One of the stringent challenges lies in difficult control of the nucleation and crystallization kinetics of the perovskites with mixed ingredients. Herein, a pre-seeding strategy by mixing FAPbI3 solution with pre-synthesized MAPbI3 microcrystals has been developed to smartly decouple the nucleation and crystallization process. As a result, the time window of initialized crystallization has been greatly extended by 3 folds (i.e. from 5 s to 20 s), which enables the formation of uniform and homogeneous alloyed-FAMA perovskite films with designated stoichiometric ratios. The resultant blade-coated solar cells achieved a champion efficiency of 24.31 % accompanied by outstanding reproducibility with more than 87 % of the devices showing efficiencies higher than 23 %.

Monodisperse Adducts-Induced Homogeneous Nucleation Towards High-Quality Tin-Based Perovskite Film.

The classic solvent system can't sufficiently separate one-dimensional edge-sharing SnI2 crystals in solution, which severely restricts the fabrication of high-quality tin-based perovskite film. Herein, a strong Lewis base (hexamethylphosphoramide, HMPA) has been introduced to coordinate Sn2+ to modulate solvation behaviours on perovskite precursor and regulate crystallization kinetics. The large molecular volume of HMPA and stronger bind energy of SnI2 ⋅ 2HMPA (-0.595 eV vs -0.118 eV for SnI2 ⋅ 2DMSO) change the solvation structure of SnI2 from edge-sharing cluster to monodisperse adduct, which contributes to uniform nucleation sites and prolongs crystal growth process. Delightfully, a fully-covered perovskite film is formed on the large-area substrate and tin-based perovskite solar cells processed with HMPA exhibit an excellent efficiency of 13.46 %. This research provides novel insights and directions for the solution preparation of smooth and uniform large-area tin-based perovskite film.

Diammonium Molecular Configuration-Induced Regulation of Crystal Orientation and Carrier Dynamics for Highly Efficient and Stable 2D/3D Perovskite Solar Cells.

The effects from the molecular configuration of diammonium spacer cations on 2D/3D perovskite properties are still unclear. Here, we investigated systematically the mechanism of molecular configuration-induced regulation of crystallization kinetic and carrier dynamics by employing various diammonium molecules to construct Dion-Jacobson (DJ)-type 2D/3D perovskites to further facilitating the photovoltaic performance. The minimum average Pb-I-Pb angle leads to the smallest octahedral tilting of [PbX6 ]4- lattice in optimal diammonium molecule-incorporated DJ-type 2D/3D perovskite, which enables suitable binding energy and hydrogen-bonding between spacer cations and inorganic [PbX6 ]4- cages, thus contributing to the formation of high-quality perovskite film with vertical crystal orientation, mitigatory lattice distortion and efficient carrier transportation. As a consequence, a dramatically improved device efficiency of 22.68 % is achieved with excellent moisture stability.

Multidentate Chelation Heals Structural Imperfections for Minimized Recombination Loss in Lead-Free Perovskite Solar Cells.

Tin-based perovskite solar cells (Sn-PSCs) have emerged as promising environmentally viable photovoltaic technologies, but still suffer from severe non-radiative recombination loss due to the presence of abundant deep-level defects in the perovskite film and under-optimized carrier dynamics throughout the device. Herein, we healed the structural imperfections of Sn perovskites in an "inside-out" manner by incorporating a new class of biocompatible chelating agent with multidentate claws, namely, 2-Guanidinoacetic acid (GAA), which passivated a variety of deep-level Sn-related and I-related defects, cooperatively reinforced the passivation efficacy, released the lattice strain, improved the structural toughness, and promoted the carrier transport of Sn perovskites. Encouragingly, an efficiency of 13.7 % with a small voltage deficit of ≈0.47 V has been achieved for the GAA-modified Sn-PSCs. GAA modification also extended the lifespan of Sn-PSCs over 1200 hours.

Advances in the Application of Perovskite Materials.

Nowadays, the soar of photovoltaic performance of perovskite solar cells has set off a fever in the study of metal halide perovskite materials. The excellent optoelectronic properties and defect tolerance feature allow metal halide perovskite to be employed in a wide variety of applications. This article provides a holistic review over the current progress and future prospects of metal halide perovskite materials in representative promising applications, including traditional optoelectronic devices (solar cells, light-emitting diodes, photodetectors, lasers), and cutting-edge technologies in terms of neuromorphic devices (artificial synapses and memristors) and pressure-induced emission. This review highlights the fundamentals, the current progress and the remaining challenges for each application, aiming to provide a comprehensive overview of the development status and a navigation of future research for metal halide perovskite materials and devices.

Ionic Liquid-Induced Ostwald Ripening Effect for Efficient and Stable Tin-Based Perovskite Solar Cells.

Tin-based perovskite solar cells (PVSCs) are regarded as the most promising alternative among lead-free PVSCs. However, the rapid crystallization for tin-based perovskite tends to cause inferior film morphology and abundant defect states, which make poor photovoltaic performance. Here, 1-butyl-3-methylimidazolium bromide (BMIBr) ionic liquids (ILs) with strong polarity and a low melting point are first employed to produce the Ostwald ripening effect and obtain high-quality tin-based perovskite films with a large grain size. Meanwhile, the non-radiative recombination ascribed from defect states can also be effectively reduced for BMIBr-treated perovskite films. Consequently, a photoelectric conversion efficiency (PCE) of 10.09% for inverted tin-based PVSCs is attained by the Ostwald ripening effect. Moreover, the unencapsulated devices with BMIBr retain near 85% of the original PCE in a N2 glovebox beyond 1200 h and about 40% of the original PCE after exposure to air for 48 h.

Regulated Crystallization of Efficient and Stable Tin-Based Perovskite Solar Cells via a Self-Sealing Polymer.

Tin-based perovskite solar cells (PVSCs) have emerged as the most promising lead-free perovskite materials owing to their superior optoelectronic properties. However, the deficiency of accurate control of the tin-based perovskite crystallization process increases the possibility of unexpected perovskite film morphology and defects, resulting in inferior power conversion efficiency (PCE). Meanwhile, the poor environmental stability of tin-based perovskite films hinders its further development. In this work, a unique polymer [poly(ethylene-co-vinyl acetate) (EVA)] is introduced into anti-solvent during spin coating of formamidinium tin tri-iodide (FASnI3) precursor solution. The C═O groups contained in EVA have a powerful Lewis acid-base complexation with uncoordinated tin atoms in perovskite grains, which can greatly improve the grain size, optimize the grain orientation, and decrease the surface defects of FASnI3 films. This strategy offers an impressive PCE of 7.72% with favorable reproducibility. More importantly, the PVSC devices based on FASnI3-EVA absorbers have a self-encapsulation effect, which exhibits distinguished moisture and oxygen barrier property, thereby retaining 62.4% of the original efficiency value after aging for 48 h in the air with a humidity of 60%. Such a convenient strategy provides a new inspiration for the establishment of stable and high-performance tin-based PVSCs.

Preparation of efficient inverted tin-based perovskite solar cells via the bidentate coordination effect of 8-hydroxyquinoline.

The N and O atoms in the bidentate ligand 8-hydroxyquinoline (8-HQ) can simultaneously coordinate with Sn2+, which greatly inhibits the oxidation of Sn2+. The formation of complexes improves the quality of FASnI3 films and reduces defect states, resulting in improvements in the efficiency and stability of FASnI3-based perovskite solar cells.

Controlling Crystal Growth via an Autonomously Longitudinal Scaffold for Planar Perovskite Solar Cells.

Sequential deposition is certified as an effective technology to obtain high-performance perovskite solar cells (PVSCs), which can be derivatized into large-scale industrial production. However, dense lead iodide (PbI2 ) causes incomplete reaction and unsatisfactory solution utilization of perovskite in planar PVSCs without mesoporous titanium dioxide as a support. Here, a novel autonomously longitudinal scaffold constructed by the interspersion of in situ self-polymerized methyl methacrylate (sMMA) in PbI2 is introduced to fabricate efficient PVSCs with excellent flexural endurance and environmental adaptability. By this strategy perovskite solution can be confined within an organic scaffold with vertical crystal growth promoted, effectively inhibiting exciton accumulation and recombination at grain boundaries. Additionally, sMMA cross-linked perovskite network can release mechanical stress and occupy the main channels for ion migration and water/oxygen permeation to significantly improve operational stability, which opens up a new strategy for the commercial development of large-area PVSCs in flexible electronics.