Carbon-based interlayers in perovskite solar cells

Perovskites are solution-processed, high-performance semiconductors of interest in low-cost photovoltaics. The interfaces between the perovskite photoactive layers and the top and bottom contacts are crucial for efficient charge transport and minimizing trapping. Control of the collection of charge carriers at these interfaces is decisive to device performance. Here, we review recent progress in the realization of efficient perovskite solar cells using cheap, easily processed, stable, carbon-based interlayers. Interface materials including graphene, carbon nanotubes, fullerenes, graphene quantum dots and carbon dots are introduced and their influence on device performance is discussed

Photoluminescence of Lead Sulfide Quantum Dots of Different Sizes in a Nanoporous Silicate Glass Matrix

The optical properties of lead sulfide quantum dots (QDs) of different sizes embedded in a nanoporous silicate glass matrix (NSM) are investigated by steady-state and transient photoluminescence spectroscopy. The use of this matrix allows the fabrication of samples with reproducible optical characteristics, for both isolated and close-packed QDs. Low-temperature PL analysis of isolated QDs with sizes of 3.7 and 4.5 nm shows that the coefficient of temperature shift of the PL position changes sign with reducing QD size because of size-dependent contributions from thermal expansion, mechanical strain, and electron–phonon coupling. The PL intensity is determined by size-dependent splitting of the lowest energy electronic state

Beyond Charge Transfer: The impact of auger recombination and FRET on PL quenching in an rGO-QDs system

PL intensity quenching and the PL lifetime reduction of fluorophores located close to gra‐ phene derivatives are generally explained by charge and energy transfer processes. Analyzing the PL from PbS QDs in rGO/QD systems, we observed a substantial reduction in average PL lifetimes with an increase in rGO content that cannot be interpreted solely by these two processes. To explain the PL lifetime dependence on the rGO/QD component ratio, we propose a model based on the Auger recombination of excitations involving excess holes left in the QDs after the charge transfer process. To validate the model, we conducted additional experiments involving the external engi‐ neering of free charge carriers, which confirmed the role of excess holes as the main QD PL quench‐ ing source. A mathematical simulation of the model demonstrated that the energy transfer between neighboring QDs must also be considered to explain the experimental data carefully. Together, Au‐ ger recombination and energy transfer simulation offers us an excellent fit for the average PL life‐ time dependence on the component ratio of the rGO/QD system

Ytterbium-Doped Lead–Halide Perovskite Nanocrystals: Synthesis, Near-Infrared Emission, and Open-Source Machine Learning Model for Prediction of Optical Properties

Lead–halide perovskite nanocrystals are an attractive class of materials since they can be easily fabricated, their optical properties can be tuned all over the visible spectral range, and they possess high emission quantum yields and narrow photoluminescence linewidths. Doping perovskites with lanthanides is one of the ways to widen the spectral range of their emission, making them attractive for further applications. Herein, we summarize the recent progress in the synthesis of ytterbium-doped perovskite nanocrystals in terms of the varying synthesis parameters such as temperature, ligand molar ratio, ytterbium precursor type, and dopant content. We further consider the dependence of morphology (size and ytterbium content) and optical parameters (photoluminescence quantum yield in visible and near-infrared spectral ranges) on the synthesis parameters. The developed open-source code approximates those dependencies as multiple-parameter linear regression and allows us to estimate the value of the photoluminescence quantum yield from the parameters of the perovskite synthesis. Further use and promotion of an open-source database will expand the possibilities of the developed code to predict the synthesis protocols for doped perovskite nanocrystals

Band Structure and Intersubband Transitions of Three-Layer Semiconductor Nanoplatelets

This paper presents the first general theory of electronic band structure and intersubband transitions in three-layer semiconductor nanoplatelets. We find a dispersion relation and wave functions of the confined electrons and use them to analyze the band structure of core/shell nanoplatelets with equal thicknesses of the shell layers. It is shown that the energies of electrons localized inside the shell layers can be degenerate for certain electron wave vectors and certain core and shell thicknesses. We also show that the energies of intersubband transitions can be nonmonotonic functions of the core and shell thicknesses, exhibiting pronounced local minima and maxima which can be observed in the infrared absorption spectra. Our results will prove useful for the design of photonic devices based on multilayered semiconductor nanoplatelets operating at infrared frequencies

Improved One- and Multiple-Photon Excited Photoluminescence from Cd2+-Doped CsPbBr3 Perovskite NCs

Metal halide perovskite nanocrystals (NCs) attract much attention for light-emitting applications due to their exceptional optical properties. More recently, perovskite NCs have begun to be considered a promising material for nonlinear optical applications. Numerous strategies have recently been developed to improve the properties of metal halide perovskite NCs. Among them, B-site doping is one of the most promising ways to enhance their brightness and stability. However, there is a lack of study of the influence of B-site doping on the nonlinear optical properties of inorganic perovskite NCs. Here, we demonstrate that Cd2+ doping simultaneously improves both the linear (higher photoluminescence quantum yield, larger exciton binding energy, reduced trap states density, and faster radiative recombination) and nonlinear (higher two- and three-photon absorption cross-sections) optical properties of CsPbBr3 NCs. Cd2+ doping results in a two-photon absorption cross-section, reaching 2.6 × 106 Goeppert-Mayer (GM), which is among the highest reported for CsPbBr3 NCs

Functionalized rGO Interlayers Improve the Fill Factor and Current Density in PbS QDs-Based Solar Cells

Graphene-quantum dot nanocomposites attract significant attention for novel optoelectronic devices, such as ultrafast photodetectors and third-generation solar cells. Combining the remarkable optical properties of quantum dots (QDs) with the exceptional electrical properties of graphene derivatives opens a vast perspective for further growth in solar cell efficiency. Here, we applied (3-mercaptopropyl) trimethoxysilane functionalized reduced graphene oxide (f-rGO) to improve the QDs-based solar cell active layer. The different strategies of f-rGO embedding are explored. When f-rGO interlayers are inserted between PbS QD layers, the solar cells demonstrate a higher current density and a better fill factor. A combined study of the morphological and electrical parameters of the solar cells shows that the improved efficiency is associated with better layer homogeneity, lower trap-state densities, higher charge carrier concentrations, and the blocking of the minor charge carriers