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The metal oxide electron transport layers (ETLs) of n-i-p perovskite solar cells (PSCs) are dominated by TiO2 and SnO2, while the efficacy of the other metal oxide ETLs still lags far behind. Herein, an emerging, economical, and environmentally friendly metal oxide, antimony oxide (Sb2Ox, x = 2.17), prepared by chemical bath deposition is reported as an alternative ETL for PSCs. The deposited Sb2Ox film is amorphous and very thin (â¼10 nm) but conformal on rough fluorine-doped tin oxide substrates, showing matched energy levels, efficient electron extraction, and then reduced nonradiative recombination in PSCs. The champion PSC based on the Sb2Ox ETL delivers an impressive power conversion efficiency of 24.7% under one sun illumination, which represents the state-of-the-art performance of all metal oxide ETL-based PSCs. Additionally, the Sb2Ox-based devices show improved operational and thermal stability compared to their SnO2-based counterparts. Armed with these findings, we believe this work offers an optional ETL for perovskites-based optoelectronic devices.
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Colloidal quantum dots with lower surface ligand density are desired for preparing the active layer for photovoltaic, lighting, and other potential optoelectronic applications. In emerging perovskite quantum dots (PQDs), the diffusion of cations is thought to have a high energy barrier, relative to that of halide anions. Herein, we investigate the fast cross cation exchange approach in colloidal lead triiodide PQDs containing methylammonium (MA+) and formamidinium (FA+) organic cations, which exhibits a significantly lower exchange barrier than inorganic cesium (Cs+)-FA+ and Cs+-MA+ systems. First-principles calculations further suggest that the fast internal cation diffusion arises due to a lowering in structural distortions and the consequent decline in attractive cation-cation and cation-anion interactions in the presence of organic cation vacancies in mixed MA+-FA+ PQDs. Combining both experimental and theoretical evidence, we propose a vacancy-assisted exchange model to understand the impact of structural features and intermolecular interaction in PQDs with fewer surface ligands. Finally, for a realistic outcome, the as-prepared mixed-cation PQDs display better photostability and can be directly applied for one-step coated photovoltaic and photodetector devices, achieving a high photovoltaic efficiency of 15.05% using MA0.5FA0.5PbI3 PQDs and more precisely tunable detective spectral response from visible to near-infrared regions.
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Ruddlesden-Popper (RP) interface with defined stacking structure will fundamentally influence the optoelectronic performances of lead-halide perovskite (LHP) materials and devices. However, it remains challenging to observe the atomic local structures in LHPs, especially for multi-dimensional RP interface hidden inside the nanocrystal. In this work, the advantages of two imaging modes in scanning transmission electron microscopy (STEM), including high-angle annular dark field (HAADF) and integrated differential phase contrast (iDPC) STEM, are successfully combined to study the bulk and local structures of inorganic and organic/inorganic hybrid LHP nanocrystals. Then, the multi-dimensional RP interfaces in these LHPs are atomically resolved with clear gap and blurred transition region, respectively. In particular, the complex interface by the RP stacking in 3D directions can be analyzed in 2D projected image. Finally, the phase transition, ion missing, and electronic structures related to this interface are investigated. These results provide real-space evidence for observing and analyzing atomic multi-dimensional RP interfaces, which may help to better understand the structure-property relation of LHPs, especially their complex local structures.
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This study demonstrates an acetate ligand (AcO-)-assisted strategy for the controllable and tunable synthesis of colloidal methylammonium lead iodide (MAPbI3) perovskite nanocrystals (PNCs) for efficient photovoltaic and photodetector devices. The size of colloidal MAPbI3 PNCs can be tuned from 9 to 20 nm by changing the AcO-/MA ratio in the reaction precursor. In situ observations and detailed characterization results show that the incorporation of the AcO- ligand alters the formation of PbI6 octahedral cages, which controls PNC growth. A well-optimized AcO-/MA ratio affords MAPbI3 PNCs with a low defect density, a long carrier lifetime, and unique solid-state isotropic properties, which can be used to fabricate solution-processed dual-mode photovoltaic and photodetector devices with a conversion efficiency of 13.34% and a detectivity of 2 × 1011 Jones, respectively. This study provides an avenue to further the precisely controllable synthesis of hybrid PNCs for multifunctional optoelectronic applications.
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Lead halide perovskite solar cells (PSCs) have made unprecedented progress, exhibiting great potential for commercialization. Among them, inverted p-i-n PSCs provide outstanding compatibility with flexible substrates, more importantly, with silicon (Si) bottom devices for higher efficiency perovskite-Si tandem solar cells. However, even with recently obtained efficiency over 25%, the investigation of inverted p-i-n PSCs is still behind the n-i-p counterpart so far. Recent progress has demonstrated that the fill factor (FF) in inverted PSCs currently still underperforms relative to open-circuit voltage and short-circuit current density, which requires an in-depth understanding of the mechanism and further research. In this review article, the recent advancements in high FF inverted PSCs by adopting the approaches of interfacial optimization, precursor engineering as well as fabrication techniques to minimize undesirable recombination are summarized. Insufficient carrier extraction and transport efficiency are found to be the main factors that hinder the current FF of inverted PSCs. In addition, insights into the main factors limiting FF and strategies for minimizing series resistance in inverted PSCs are presented. The continuous efforts dedicated to the FF of high-performance inverted devices may pave the way toward commercial applications of PSCs in the near future.
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Chemical bath deposited (CBD) SnO2 is one of the most prevailing electron transport layers for realizing high-efficiency perovskite solar cells (PSCs) so far. However, the state-of-the-art CBD SnO2 process is time-consuming, contradictory to its prospect in industrialization. Herein, a simplified yet efficient method is developed for the fast deposition of SnO2 electrodes by incorporating a concentrated Sn source stabilized by the ethanol ligand with antimony (Sb) doping. The higher concentration of Sn source promotes the deposition rate, and Sb doping improves the hole-blocking capability of the CBD SnO2 layer so that its target thickness can be reduced to further save the deposition time. As a result, the deposition time can be appreciably reduced from 3-4 h to only 5 min while maintaining 95% of the maximum efficiency, indicating the power of the method toward high-throughput production of efficient PSCs. Additionally, the CBD SnO2 substrates are recyclable after removing the upper layers of complete PSCs, and the refurbished PSCs can maintain ≈98% of their initial efficiency after three recycling-and-fabrication processes.
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For emerging perovskite quantum dots (QDs), understanding the surface features and their impact on the materials and devices is becoming increasingly urgent. In this family, hybrid FAPbI3 QDs (FA: formamidium) exhibit higher ambient stability, near-infrared absorption and sufficient carrier lifetime. However, hybrid QDs suffer from difficulty in modulating surface ligand, which is essential for constructing conductive QD arrays for photovoltaics. Herein, assisted by an ionic liquid formamidine thiocyanate, we report a facile surface reconfiguration methodology to modulate surface and manipulate electronic coupling of FAPbI3 QDs, which is exploited to enhance charge transport for fabricating high-quality QD arrays and photovoltaic devices. Finally, a record-high efficiency approaching 15 % is achieved for FAPbI3 QD solar cells, and they retain over 80 % of the initial efficiency after aging in ambient environment (20-30 % humidity, 25 °C) for over 600â h.
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The mixed cation colloidal Cs1-XFAXPbI3 perovskite quantum dots (PQDs) obtained by cation exchange between CsPbI3 and FAPbI3 PQDs have been reported to exhibit enhanced photovoltaic performance. However, the cation exchange mechanism requires further in-depth investigation in terms of both material properties and device application. In this work, the impact of PQD weight ratio, PQD concentration, and host solvent polarity during cation exchange is comprehensively investigated for the first time. In addition, the whole exchange process under varying conditions is monitored by photoluminescence spectroscopy. As a result, we observe extremely fast cation exchange (â¼20 min) under a condition at a CsPbI3/FAPbI3 PQD weight ratio of 1:1, a concentration of 70 mg/ml, and a host solvent using toluene. Moreover, we directly fabricate a PQD solar cell device using these obtained mixed cation Cs0.5FA0.5PbI3 PQDs and achieved an enhanced power conversion efficiency of 14.58%. We believe that these results would provide more insights into the cation exchange in emerging PQDs toward efficient photovoltaic fabrication and application.
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Data are a strategic resource for industrial production, and an efficient data-mining process will increase productivity. However, there exist many missing values in data collected in real life due to various problems. Because the missing data may reduce productivity, missing value imputation is an important research topic in data mining. At present, most studies mainly focus on imputation methods for continuous missing data, while a few concentrate on discrete missing data. In this paper, a discrete missing value imputation method based on a multilayer perceptron (MLP) is proposed, which employs a momentum gradient descent algorithm, and some prefilling strategies are utilized to improve the convergence speed of the MLP. To verify the effectiveness of the method, experiments are conducted to compare the classification accuracy with eight common imputation methods, such as the mode, random, hot-deck, KNN, autoencoder, and MLP, under different missing mechanisms and missing proportions. Experimental results verify that the improved MLP model (IMLP) can effectively impute discrete missing values in most situations under three missing patterns.
Assuntos
Algoritmos , Redes Neurais de Computação , Mineração de Dados , Movimento (Física) , Projetos de PesquisaRESUMO
Ruddlesden-Popper phase 2D perovskite solar cells (PSCs) exhibit improved lifetime while still facing challenges such as phase alignment and up-scaling to module-level devices. Herein, polyelectrolytes are explored to tackle this issue. The contact between perovskite and hole-transport layer (HTL) is important for decreasing interfacial non-radiative recombination and scalable fabrication of uniform 2D perovskite films. Through exploring compatible butylamine cations, we first demonstrate poly(3-(4-carboxybutyl)thiophene-2,5-diyl)-butylamine (P3CT-BA) as an efficient HTL for 2D PSCs due to its great hydrophilicity, relatively high hole mobility and uniform surface. More importantly, the tailored P3CT-BA has an anchoring effect and acts as the buried passivator for 2D perovskites. Consequently, a best efficiency approaching 18 % was achieved and we further first report large-area (2×3â cm2 , 5×5â cm2 ) 2D perovskite minimodules with an impressive efficiency of 14.81 % and 11.13 %, respectively.
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α-Formamidinium lead iodide (α-FAPbI3 ) is one of the most promising candidate materials for high-efficiency and thermally stable perovskite solar cells (PSCs) owing to its outstanding optoelectrical properties and high thermal stability. However, achieving a stable form of α-FAPbI3 where both the composition and the phase are pure is very challenging. Herein, we report on a combined strategy of precursor engineering and grain anchoring to successfully prepare methylammonium (MA)-free and phase-pure stable α-FAPbI3 films. The incorporation of volatile FA-based additives in the precursor solutions completely suppresses the formation of non-perovskite δ-FAPbI3 during film crystallization. Grains of the desired α-phase are anchored together and stabilized when 4-tert-butylbenzylammonium iodide is permeated into the α-FAPbI3 film interior via grain boundaries. This cooperative scheme leads to a significantly increased efficiency close to 21 % for FAPbI3 perovskite solar cells. Moreover, the stabilized PSCs exhibit improved thermal stability and maintained ≈90 % of their initial efficiency after storage at 50 °C for over 1600â hours.
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To fine-tune surface ligands towards high-performance devices, we developed an inâ situ passivation process for all-inorganic cesium lead iodide (CsPbI3 ) perovskite quantum dots (QDs) by using a bifunctional ligand, L-phenylalanine (L-PHE). Through the addition of this ligand into the precursor solution during synthesis, the inâ situ treated CsPbI3 QDs display significantly reduced surface states, increased vacancy formation energy, higher photoluminescence quantum yields, and much improved stability. Consequently, the L-PHE passivated CsPbI3 QDs enabled the realization of QD solar cells with an optimal efficiency of 14.62 % and red light-emitting diodes (LEDs) with a highest external quantum efficiency (EQE) of 10.21 %, respectively, demonstrating the great potential of ligand bonding management in improving the optoelectronic properties of solution-processed perovskite QDs.
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We reported a surface ligand manipulation strategy for hybrid MAPbI3 perovskite quantum dots (PeQDs) using methylamine iodide (MAI), methylamine thiocyanate (MASCN) and methylamine acetate (MAAc) salts. After MAI salt post-treatment, a record high efficiency of 14.98% was obtained for MAPbI3 PeQD solar cells together with enhanced ambient stability.
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The lead iodide (PbI2 ) in lead-halide perovskite (LHP) is both a positive additive for material properties and a site for the formation of device defects. Therefore, atomic-level detection of PbI2 and its derived Pb structures are crucial for understanding the performance and stability of the LHP material. In this work, the atomic imaging of the LHP, PbI2 , and Pb lattices is achieved using low-dose integrated differential phase contrast (iDPC) scanning transmission electron microscopy (STEM). Combining it with the traditional high-angle annular dark field (HAADF)-STEM, the Pb precipitation in different LHPs (CsPbI3 , CsPbBr3, and FAPbI3 ) and under different conditions (light, air, and heat) can be investigated in real space. Then, the features of Pb precipitation (positions and sizes) are visually revealed under different conditions and the stabilities of different LHPs. Meanwhile, the pathway of Pb precipitation is directly imaged and confirmed by the iDPC-STEM during an in situ heating process, supporting the detailed mechanism of Pb precipitation. These results provide the visual evidence for analyzing atomic Pb precipitation in LHPs, which helps better understand the structure-property relation induced by Pb impurity.
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Defects around the surface and grain boundaries of perovskite films normally cause severe nonradiative recombination and imbalanced charge carrier transport, further limiting both the efficiency and stability of perovskite solar cells (PSCs). To tackle this critical issue, we propose a chemical bridge strategy to reconstruct the interface using organometallic molecules. The commercially available molecule bis(diphenylphosphino)ferrocene (FcP2), with a unique bridge molecular structure, anchors and chelates Pb atoms by forming strong Pb-P bonds and further passivates both surfaces and grain boundaries. Detailed characterization revealed that bridge molecule FcP2 reconstruction can effectively suppress nonradiative recombination, and the electron delocalization properties of the ferrocene core can further achieve more balanced interfacial carrier transport. The resultant N-i-P PSC device outputs close to 25% efficiency together with one of the best reported operational stabilities, maintaining over 95% of the initial efficiency after 1000 h of continuous operation at the maximum power point under 1-sun illumination.
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Climate change is one of the main challenges, and it poses a tough challenge to the agriculture industry globally. Additionally, greenhouse gas (GHG) emissions are the main contributor to climate change; however, croplands are a prominent source of GHG emissions. Yet this complex challenge can be mitigated through climate-smart agricultural practices. Conservation tillage is commonly known to preserve soil and mitigate environmental change by reducing GHG emissions. Nonetheless, there is still a paucity of information on the influences of conservation tillage on wheat yield, soil properties, and GHG flux, particularly in the semi-arid Dingxi belt. Hence, in order to fill this gap, different tillage systems, namely conventional tillage (CT) control, straw incorporation with conventional tillage (CTS), no-tillage (NT), and stubble return with no-tillage (NTS), were laid at Dingxi, Gansu province of China, under a randomized complete block design with three replications to examine their impacts on yield, soil properties, and GHG fluxes. Results depicted that different conservative tillage systems (CTS, NTS, and NT) significantly (p < 0.05) increased the plant height, number of spikes per plant, seed number per meter square, root yield, aboveground biomass yield, thousand-grain weight, grain yield, and dry matter yield compared with CT. Moreover, these conservation tillage systems notably improved the soil properties (soil gravimetric water content, water-filled pore space, water storage, porosity, aggregates, saturated hydraulic conductivity, organic carbon, light fraction organic carbon, carbon storage, microbial biomass carbon, total nitrogen, available nitrogen storage, microbial biomass nitrogen, total phosphorous, available phosphorous, total potassium, available potassium, microbial counts, urease, alkaline phosphatase, invertase, cellulase, and catalase) while decreasing the soil temperature and bulk density over CT. However, CTS, NTS, and NT had non-significant effects on ECe, pH, and stoichiometric properties (C:N ratio, C:P ratio, and N:P ratio). Additionally, conservation-based tillage regimes NTS, NT, and CTS significantly (p < 0.05) reduced the emission and net global warming potential of greenhouse gases (carbon dioxide, methane, and nitrous oxide) by 23.44, 19.57, and 16.54%, respectively, and decreased the greenhouse gas intensity by 23.20, 29.96, and 18.72%, respectively, over CT. We conclude that NTS is the best approach to increasing yield, soil and water conservation, resilience, and mitigation of agroecosystem capacity.
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In this work, we have reported for the first time a facile route for developing solution-processed Al2O3 film at a greatly reduced processing temperature and studied its applications in producing inverted polymer solar cells (PSCs). These PSCs using Al2O3 thin film as the electron-extraction layer demonstrated improved diode characteristics and achieved a 20% higher power conversion efficiency than devices using the conventional ZnO buffer layer. Furthermore, the low temperature processing of the Al2O3 film makes it compatible with fabrication of flexible organic electronic devices based on plastic substrates.
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Global climate change has led to a significant increase in the frequency of extreme rainfall events in the Qinghai-Tibetan Plateau (QTP), thus potentially increasing the annual rainfall amounts and, consequently, affecting the net soil nitrogen (N) mineralization process. However, few studies on the responses of the soil net N mineralization rates to the increases in rainfall amounts and frequencies in alpine wet meadows have been carried out. Therefore, the present study aims to assess the effects of rainfall frequency and amount changes on the N fixation capacity of wet meadow soils by varying the rainfall frequency and amount in the Gahai wet meadow in the northeastern margin of the QTP during the plant-growing season in 2019. The treatment scenarios consisted of ambient rain (CK) and supplementary irrigation at a rate of 25 mm, with different irrigation frequencies, namely weekly (DF1), biweekly (DF2), every three weeks (DF3), and every four weeks (DF4). According to the obtained results, the increased rainfall frequency and amount decreased the soil mineral N stock and increased the aboveground vegetation biomass (AB) amounts and soil water contents in the wet meadows of the QTP. Ammonium (NH4+-N) and nitrate N (NO3--N) contributed similarly to the mineral N contents. However, the ammonification process played a major role in the soil mineralization process. The effects of increasing rainfall amount and frequency on N mineralization showed seasonal variations. The N mineralization rate showed a single-peaked curve with increasing soil temperature during the rapid vegetation growth phase, reaching the highest value in August. In addition, the N mineralization rates showed significant positive correlations with soil temperatures and NH4+-N contents and a significant negative correlation with AB (P < 0.05). The results of this study demonstrated the key role of low extreme rainfall event frequencies in increasing the net soil N mineralization rates in the vegetation growing season, which is detrimental to soil N accumulation, thereby affecting the effectiveness of soil N contents.
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Despite the simplified fabrication process and desirable microstructural stability, the limited charge transport properties of block copolymers and double-cable conjugated polymers hinder the overall performance of single-component photovoltaic devices. Based on the key distinction in the donor (D)-acceptor (A) bonding patterns between single-component and bulk heterojunction (BHJ) devices, rationalizing the difference between the transport mechanisms is crucial to understanding the structure-property correlation. Herein, the barrier formed between the D-A covalent bond that hinders electron transport in a series of single-component photovoltaic devices is investigated. The electron transport in block copolymer-based devices is strongly dependent on the electric field. However, these devices demonstrate exceptional advantages with respect to the charge transport properties, involving high stability to compositional variations, improved film uniformity, and device reproducibility. This work not only illustrates the specific charge transport behavior in block copolymer-based devices but also clarifies the enormous commercial viability of large-area single-component organic solar cells (SCOSCs).
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Revealing the local structural change of metal halide perovskites (MHPs) induced by external conditions is important to understand its performance and stability in optoelectronic applications. However, previous studies on the properties and structures of MHPs are usually limited by the spatial resolution of the probe, and it is still challenging to obtain its atomic structural information in real space. In this work, the integrated differential-phase-contrast scanning transmission electron microscopy is applied to the low-dose imaging of CsPbI3 quantum dots (QDs). In particular, the local structures in QDs, such as surfaces and interfaces, can be atomically resolved. Then, the structural evolution of CsPbI3 QDs under various external conditions can be unraveled during in situ heating or ex situ treatments, where it lose cubic shapes and fuse to larger particles. The changes in surfaces and interfaces with missing Cs ions and PbI6 octahedrons can be semi-quantitatively studied by profile analysis and bond-length measurement in images. Finally, density functional theory calculations are performed to illustrate the properties and stabilities of the different structures that are observed. These results provide atomic-scale insights into the structural evolution of QDs, which is of great importance to modify the performance of perovskite materials and devices.