Perovskite solar cells (PSCs) based on the regular n–i–p device architecture have reached above 25% certified efficiency with continuously reported improvements in recent years. A key common factor ...for these recent breakthroughs is the development of SnO2 as an effective electron transport layer in these devices. In this article, the key advances in SnO2 development are reviewed, including various deposition approaches and surface treatment strategies, to enhance the bulk and interface properties of SnO2 for highly efficient and stable n–i–p PSCs. In addition, the general materials chemistry associated with SnO2 along with the corresponding materials challenges and improvement strategies are discussed, focusing on defects, intrinsic properties, and impact on device characteristics. Finally, some SnO2 implementations related to scalable processes and flexible devices are highlighted, and perspectives on the future development of efficient and stable large‐scale perovskite solar modules are also provided.
This review summarizes the recent advances of SnO2‐based perovskite solar cells (PSCs) and the related interface optimization strategies and applications. The fundamental properties of SnO2 are discussed, with a focus on the defect chemistry, and various preparation methods for improving SnO2 and SnO2/perovskite interface. Finally, the challenges and opportunities for further development of SnO2‐based PSCs are provided.
Perovskite solar cells (PSCs) have reached a certified 25.2% efficiency in 2019 due to their high absorption coefficient, high carrier mobility, long diffusion length, and tunable direct bandgap. ...However, due to the nature of solution processing and rapid crystal growth of perovskite thin films, a variety of defects can form as a result of the precursor compositions and processing conditions. The use of additives can affect perovskite crystallization and film formation, defect passivation in the bulk and/or at the surface, as well as influence the interface tuning of structure and energetics. Here, recent progress in additive engineering during perovskite film formation is discussed according to the following common categories: Lewis acid (e.g., metal cations, fullerene derivatives), Lewis base based on the donor type (e.g., O‐donor, S‐donor, and N‐donor), ammonium salts, low‐dimensional perovskites, and ionic liquid. Various additive‐assisted strategies for interface optimization are then summarized; additives include modifiers to improve electron‐ and hole‐transport layers as well as those to modify perovskite surface properties. Finally, an outlook is provided on research trends with respect to additive engineering in PSC development.
Recent progress on additive engineering during perovskite film formation is reported according to the following common categories: Lewis acid, Lewis base, ammonium salts, low‐dimensional perovskites, and ionic liquid. Then, various additive‐assisted strategies for interface optimization are compared. Finally, an outlook on the research trends with respect to additive engineering in perovskite solar cell development is provided.
This paper studies the problem of detecting the information source in a network in which the spread of information follows the popular Susceptible-Infected-Recovered (SIR) model. We assume all nodes ...in the network are in the susceptible state initially, except one single information source that is in the infected state. Susceptible nodes may then be infected by infected nodes, and infected nodes may recover and will not be infected again after recovery. Given a snapshot of the network, from which we know the graph topology and all infected nodes but cannot distinguish susceptible nodes and recovered nodes, the problem is to find the information source based on the snapshot and the network topology. We develop a sample-path-based approach where the estimator of the information source is chosen to be the root node associated with the sample path that most likely leads to the observed snapshot. We prove for infinite-trees, the estimator is a node that minimizes the maximum distance to the infected nodes. A reverse-infection algorithm is proposed to find such an estimator in general graphs. We prove that for g+1-regular trees such that gq > 1, where g+1 is the node degree and q is the infection probability, the estimator is within a constant distance from the actual source with a high probability, independent of the number of infected nodes and the time the snapshot is taken. Our simulation results show that for tree networks, the estimator produced by the reverse-infection algorithm is closer to the actual source than the one identified by the closeness centrality heuristic. We then further evaluate the performance of the reverse infection algorithm on several real-world networks.
Microplastics are emerging pollutants that have recently aroused considerable concern but most toxicological studies have focused on marine biota, with little investigation of the influence of ...microplastics on terrestrial ecosystems. Here, we fed the soil oligochaete Enchytraeus crypticus with oatmeal containing 0, 0.025, 0.5, and 10% (dry weight basis) nano-polystyrene (0.05–0.1 μm particle size) to elucidate the impact of microplastics on the growth and gut microbiome of Enchytraeus crypticus. We observed a significant reduction of weight in the animals fed 10% polystyrene and an increase in the reproduction of those fed 0.025%. More importantly, using 16S rRNA amplification and high-throughput sequencing we found a significant shift in the microbiome of those fed 10% microplastics with significant decreases in the relative abundance of the families Rhizobiaceae, Xanthobacteraceae and Isosphaeraceae. These families contain key microbes that contribute to nitrogen cycling and organic matter decomposition.
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•Exposure to nano-polystyrene disrupted the Enchytraeus crypticus microbiome.•Nano-polystyrene led to a decrease in bacterial diversity and a structural shift.•Exposure to nano-polystyrene altered the weight and reproduction of E. crypticus.
Nano-polystyrene exposure disrupted the microbiome of Enchytraeus crypticus, leading to a decrease in microbial diversity and a structural shift in bacterial composition.
We demonstrate a facile morphology-controllable sequential deposition of planar CH3NH3PbI3 (MAPbI3) film by using a novel volume-expansion-adjustable PbI2·xMAI (x: 0.1–0.3) precursor film to replace ...pure PbI2. The use of additive MAI during the first step of deposition leads to the reduced crystallinity of PbI2 and the pre-expansion of PbI2 into PbI2·xMAI with adjustable morphology, which result in about 10-fold faster formation of planar MAPbI3 film (without PbI2 residue) and thus minimize the negative impact of the solvent isopropanol on perovskites during the MAI intercalation/conversion step. The best efficiency obtained for a planar perovskite solar cell based on PbI2·0.15MAI is 17.22% (under one sun illumination), which is consistent with the stabilized maximum power output at an efficiency of 16.9%.
Hybrid organometallic halide perovskite CH3NH3PbI2Br (or MAPbI2Br) nanosheets with a 1.8 eV band gap were prepared via a thermal decomposition process from a precursor containing PbI2, MABr, and ...MACl. The planar solar cell based on the compact layer of MAPbI2Br nanosheets exhibited 10% efficiency and a single-wavelength conversion efficiency of up to 86%. The crystal phase, optical absorption, film morphology, and thermogravimetric analysis studies indicate that the thermal decomposition process strongly depends on the composition of precursors. We find that MACl functions as a glue or soft template to control the initial formation of a solid solution with the main MAPbI2Br precursor components (i.e., PbI2 and MABr). The subsequent thermal decomposition process controls the morphology/surface coverage of perovskite films on the planar substrate and strongly affects the device characteristics.
Organic and inorganic hybrid perovskites (e.g., CH3NH3PbI3) have emerged as a revolutionary class of light-absorbing semiconductors that has demonstrated a rapid increase in efficiency within a few ...years of active research. Controlling perovskite morphology and composition has been found critical to developing high-performance perovskite solar cells. The recent development of solution chemistry engineering has led to fabrication of greater than 15–17%-efficiency solar cells by multiple groups, with the highest certified 17.9% efficiency that has significantly surpassed the best-reported perovskite solar cell by vapor-phase growth. In this Perspective, we review recent progress on solution chemistry engineering processes and various control parameters that are critical to the success of solution growth of high-quality perovskite films. We discuss the importance of understanding the impact of solution-processing parameters and perovskite film architectures on the fundamental charge carrier dynamics in perovskite solar cells. The cost and stability issues of perovskite solar cells will also be discussed.
We report on the effect of TiO2 film thickness on the charge transport, recombination, and device characteristics of perovskite (CH3NH3)PbI3 sensitized solar cells using iodide-based electrolytes. ...(CH3NH3)PbI3 is relatively stable in a nonpolar solvent (e.g., ethyl acetate) with a low iodide concentration (e.g., 80 mM). Frequency-resolved modulated photocurrent/photovoltage spectroscopies show that increasing TiO2 film thickness from 1.8 to 8.3 μm has little effect on transport but increases recombination by more than 10-fold, reducing the electron diffusion length from 16.9 to 5.5 μm, which can be explained by the higher degree of iodide depletion within the TiO2 pores for thicker films. The changes of the charge-collection and light-absorption properties of (CH3NH3)PbI3 sensitized cells with varying TiO2 film thickness strongly affect the photocurrent density, photovoltage, fill factor, and solar conversion efficiency. Developing alternative, compatible redox electrolytes is important for (CH3NH3)PbI3 or similar perovskites to be used for potential photoelectrochemical applications.
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