Chloride Incorporation Process in CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> Perovskites via Nanoscale Bandgap Maps

CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> perovskites enable fabrication of highly efficient solar cells. Chloride ions benefit the morphology, carrier diffusion length, and stability of perovskite films; however, whether those benefits stem from the presence of Cl^– in the precursor solution or from their incorporation in annealed films is debated. In this work, the photothermal-induced resonance, an in situ technique with nanoscale resolution, is leveraged to measure the bandgap of CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> films obtained by a multicycle coating process that produces high efficiency (∼16%) solar cells. Because chloride ions modify the perovskite lattice, thereby widening the bandgap, measuring the bandgap locally yields the local chloride content. After a mild annealing (60 min, 60 °C) the films consist of Cl-rich (<i>x</i> < 0.3) and Cl-poor phases that upon further annealing (110 °C) evolve into a homogeneous Cl-poorer (<i>x</i> < 0.06) phase, suggesting that methylammonium-chrloride is progressively expelled from the film. Despite the small chloride content, CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> films show better thermal stability up to 140 °C with respect CH₃NH₃PbI₃ films fabricated with the same methodology

Precursor Engineering Induced High-Efficiency Electroluminescence of Quasi-Two-Dimensional Perovskites: A Synergistic Defect Inhibition and Passivation Approach

Despite light-emitting diodes (LEDs) based on quasi-two-dimensional (Q-2D) perovskites being inexpensive and exhibiting high performance, defects still limit the improvement of electroluminescence efficiency and stability by causing nonradiative recombination. Here, an organic molecule, 1-(o-tolyl) biguanide, is used to simultaneously inhibit and passivate defects of Q-2D perovskites via in situ synchronous crystallization. This molecule not only prevents surface bromine vacancies from forming through hydrogen bonding with the bromine of intermediaries but also passivates surface defects through its interaction with uncoordinated Pb. Via combination of defect inhibition and passivation, the trap density of Q-2D perovskite films can be significantly reduced, and the emission efficiency of the film can be improved. Consequently, the corresponding LED shows an external quantum efficiency of 24.3%, and its operational stability has been increased nearly 15 times

Data for: A study of indoor air quality and passengers’ thermal comfort of metro transfer stations in Beijing

Field test data and experimental calculation data

Synthesis of Cu_2–<i>x</i>Se Nanocrystals by Tuning the Reactivity of Se

In this paper, we demonstrated a modified hot-injection method to synthesize high-quality Cu2–xSe nanocrystals (NCs) in liquid paraffin without using the hazardous and unstable alkylphosphines as the ligand of Se. The key of this method is the capability for tuning the reactivity of Se at the stage of formation of Cu2–xSe nuclei. The low reactivity of Se facilitated the decomposition of copper(II) acetylacetonate into Cu2O, whereas the increase of Se reactivity promoted the reaction between Cu and Se. By control of the experimental variables, such as reaction time, Se concentration, reaction temperature, and, particularly, the addition of the noncoordinating solvent of Se, high-quality Cu2–xSe NCs were prepared. The resultant Cu2–xSe NCs possessed an indirect band-gap absorption around 1050 nm, potentially applicable in photovoltaic investigations. As an example, the optoelectronic properties of Cu2–xSe NCs were investigated, which showed a promising increase in photocurrent under AM 1.5 illumination. Because the current method was convenient and environmentally friendly, it was believed that this work would facilitate the development of a preparation technique and industrial application of copper-based photovoltaic devices

Data for: A study of indoor air quality and passengers’ thermal comfort of metro transfer stations in Beijing

Field test data and experimental calculation data

Charge Carrier Lifetimes Exceeding 15 μs in Methylammonium Lead Iodide Single Crystals

The charge carrier lifetime in organic–inorganic perovskites is one of the most important parameters for modeling and design of solar cells and other types of devices. In this work, we use CH₃NH₃PbI₃ single crystal as a model system to study optical absorption, charge carrier generation, and recombination lifetimes. We show that commonly applied photoluminescence lifetime measurements may dramatically underestimate the intrinsic carrier lifetime in CH₃NH₃PbI₃, which could be due to severe charge recombination at the crystal surface and/or fast electron–hole recombination close to the surface. By using the time-resolved microwave conductivity technique, we investigated the lifetime of free mobile charges inside the crystals. Most importantly, we find that for homogeneous excitation throughout the crystal, the charge carrier lifetime exceeds 15 μs. This means that the diffusion length in CH₃NH₃PbI₃ can be as large as 50 μm if it is no longer limited by the dimensions of the crystallites

Pressure-Induced Emission from All-Inorganic Two-Dimensional Vacancy-Ordered Lead-Free Metal Halide Perovskite Nanocrystals

Although seeking an effective strategy for further improving their optical properties is a great challenge, two-dimensional (2D) halide perovskites have attracted a significant amount of attention because of their performance. In this regard, the pressure-induced emission accompanied by a remarkable pressure-enhanced emission is achieved without a phase transition in 2D vacancy-ordered perovskite Cs3Bi2Cl9 nanocrystals (NCs). Note that the initial Cs3Bi2Cl9 NCs possess extremely strong electron–phonon coupling, leading to the easy annihilation of trapped excitons by the phonon. Upon compression, pressure could effectively suppress phonon-assisted nonradiative decay and give rise to an intriguing emission from “0” to “1”. Both the weakened electron–phonon coupling and the relaxed halide octahedral distortion benefiting from the vacancy-ordered structure contributed to the subsequent enhanced emission. This work not only elucidates the underlying photophysical mechanism but also identifies pressure engineering as a robust means for improving their potential applications in environmentally friendly solid-state lighting at extremes

Hole Extraction Enhancement for Efficient Polymer Solar Cells with Boronic Acid Functionalized Carbon Nanotubes doped Hole Transport Layers

Boronic acid functionalized multiwalled carbon nanotubes (bf-MWCNTs) were synthesized via a facile low temperature process and introduced in PEDOT:PSS as the composite hole transport layer (HTL), which improved the power conversion efficiency (PCE) of polymer solar cells (PSCs). The devices utilized PCDTBT:PC₇₁BM active layers had achieved an optimal PCE of 6.953%, leading to 28% enhancement comparing to the device based on pristine PEDOT:PSS HTL. The PEDOT:PSS:bf-MWCNTs composite HTLs exhibited remarkable enhancement on hole mobility and electrical conductivity, which were beneficial to the hole extraction and transport on interface. Meanwhile, the work function (WF) of HTLs had an increase after bf-MWCNTs doping, which was matched with the highest occupied molecular orbital (HOMO) of the donor material, further improving the hole transport. Therefore, the incorporation of bf-MWCNTs efficiently improved the hole extraction and transport from active layer to the electrode

Self-Trapped Exciton Emission Enhancement in 3D Cationic Lead Halide Hybrids Via Phase Transition Engineering

Three-dimensional (3D) cationic lead halide hybrids constructed by organic ions and inorganic networks via coordination bonds are a promising material for solid-state lighting due to their exceptional environmental stability and broad-spectrum emission. Nevertheless, their fluorescence properties are hindered by the limited lattice distortion from extensive connectivity within the inorganic network. Here, a dramatic 100-fold enhancement of self-trapped exciton (STE) emission is achieved in 3D hybrid material [Pb2Br2]­[O2C­(CH2)4CO2] via pressure-triggered phase transition. Notably, pressure-treated material exhibits a 110 nm redshift with 1.5-fold enhancement compared to the initial state after pressure was completely released. The irreversible structural phase transition intensifies the [PbBr3O3] octahedral distortion, which is highly responsible for the optimization of quenched emission. These findings present a promising strategy for improving the optical properties of 3D halide hybrids with relatively high stability and thus facilitate their practical applications by pressure-driven phase transition engineering