Passivating Grain Boundaries via Graphene Additive for Efficient Kesterite Solar Cells.

Grain boundaries (GBs)-triggered severe non-radiative recombination is recently recognized as the main culprits for carrier loss in polycrystalline kesterite photovoltaic devices. Accordingly, further optimization of kesterite-based thin film solar cells critically depends on passivating the grain interfaces of polycrystalline Cu2 ZnSn(S,Se)4 (CZTSSe) thin films. Herein, 2D material of graphene is first chosen as a passivator to improve the detrimental GBs. By adding graphene dispersion to the CZTSSe precursor solution, single-layer graphene is successfully introduced into the GBs of CZTSSe absorber. Due to the high carrier mobility and electrical conductivity of graphene, GBs in the CZTSSe films are transforming into electrically benign and do not act as high recombination sites for carrier. Consequently, benefitting from the significant passivation effect of GBs, the use of 0.05 wt% graphene additives increases the efficiency of CZTSSe solar cells from 10.40% to 12.90%, one of the highest for this type of cells. These results demonstrate a new route to further increase kesterite-based solar cell efficiency by additive engineering.

Managing Multiple Halide-Related Defects for Efficient and Stable Inorganic Perovskite Solar Cells.

Halide-related surface defects on inorganic halide perovskite not only induce charge recombination but also severely limit the long-term stability of perovskite solar cells. Herein, adopting density functional theory calculation, we verify that iodine interstitials (Ii ) has a low formation energy similar to that of the iodine vacancy (VI ) and is also readily formed on the surface of all-inorganic perovskite, and it is regarded to function as an electron trap. We screen a specific 2,6-diaminopyridine (2,6-DAPy) passivator, which, with the aid of the combined effects from halogen-Npyridine and coordination bonds, not only successfully eliminates the Ii and dissociative I2 but also passivates the abundant VI . Furthermore, the two symmetric neighboring -NH2 groups interact with adjacent halides of the octahedral cluster by forming hydrogen bonds, which further promotes the adsorption of 2,6-DAPy molecules onto the perovskite surface. Such synergetic effects can significantly passivate harmful iodine-related defects and undercoordinated Pb2+ , prolong carrier lifetimes and facilitate the interfacial hole transfer. Consequently, these merits enhance the power-conversion efficiency (PCE) from 19.6 % to 21.8 %, the highest value for this type of solar cells, just as importantly, the 2,6-DAPy-treated CsPbI3-x Brx films show better environmental stability.

Fluorine-Containing Passivation Layer via Surface Chelation for Inorganic Perovskite Solar Cells.

Minimizing surface defect is vital to further improve power conversion efficiency (PCE) and stability of inorganic perovskite solar cells (PSCs). Herein, we designed a passivator trifluoroacetamidine (TFA) to suppress CsPbI3-x Brx film defects. The amidine group of TFA can strongly chelate onto the perovskite surface to suppress the iodide vacancy, strengthened by additional hydrogen bonds. Moreover, three fluorine atoms allow strong intermolecular connection via intermolecular hydrogen bonds, thus constructing a robust shield against moisture. The TFA-treated PSCs exhibit remarkably suppressed recombination, yielding the record PCEs of 21.35 % and 17.21 % for 0.09 cm2 and 1.0 cm2 device areas, both of which are the highest for all-inorganic PSCs so far. The device also achieves a PCE of 39.78 % under indoor illumination, the highest for all-inorganic indoor photovoltaic devices. Furthermore, TFA greatly improves device ambient stability by preserving 93 % of the initial PCE after 960 h.

Synchronous Surface Reconstruction and Defect Passivation for High-Performance Inorganic Perovskite Solar Cells.

The nonradiative charge recombination caused by surface defects and inferior crystalline quality are major roadblocks to further enhancing the performance of CsPbI3- x Brx perovskite solar cells (PSCs). Theoretical calculations indicate that sodium diethyldithiocarbamate (NaDDTC), a popular bacteriostatic benign material, can initiate multiple interactions with the CsPbI3- x Brx perovskite surface to effectively passivate the defects. The experimental results reveal that the NaDDTC can indeed passivate the electron trap states and lock active sites for charge traps and water adsorption. In addition, it is found that a solid-state reaction is triggered for perovskite crystal regrowth by the NaDDTC post-treatment, which not only enlarges grain size for reducing the density of grain boundary defects but also compensates some surface defects induced by the primary film growth. Consequently, the power conversion efficiency (PCE) of the CsPbI3- x Brx PSC is increased to as high as 20.40%, with significant improvement in fill factor and open-circuit voltage (VOC ), making it one of the highest for this type of solar cell. Furthermore, the optimized devices exhibit better environmental stability. Overall, this robust synchronous strategy provides efficient surface reconstruction and defect passivation for achieving both high PCE and stable inorganic perovskite.

A highly porous animal bone-derived char with a superiority of promoting nZVI for Cr(VI) sequestration in agricultural soils.

Paddy soil and irrigation water are commonly contaminated with hexavalent chromium [Cr(VI)] near urban industrial areas, thereby threatening the safety of agricultural products and human health. In this study, we develop a porous and high specific area bone char (BC) to support nanoscale zero-valent iron (nZVI) and apply it to remediate Cr(VI) pollution in water and paddy soil under anaerobic conditions. The batch experiments reveal that BC/nZVI exhibits a higher removal capacity of 516.7 mg/(g•nZVI) for Cr(VI) than nZVI when normalized to the actual nZVI content, which is 2.8 times that of nZVI; moreover, the highest nZVI utilization is the nZVI loading of 15% (BC/nZVI15). The Cr(VI) removal efficiency of BC/nZVI15 decreases with increasing pH (4 - 10). Coexisting ions (phosphate and carbonate) and humic acid can inhibit the removal of Cr(VI) with BC/nZVI15. Additionally, BC exhibits a strong advantage in promoting Cr(VI) removal by nZVI compared to the widely used biochar and activated carbon. Our results demonstrate that reduction and coprecipitation are the dominant Cr(VI) removal mechanisms. Furthermore, BC/nZVI15 shows a significantly higher reduction and removal efficiency as well as a strong anti-interference ability for Cr(VI) in paddy soil, as compared to nZVI. These findings provide a new effective material for remediating Cr(VI) pollution from water and soil.

Rational Surface-Defect Control via Designed Passivation for High-Efficiency Inorganic Perovskite Solar Cells.

Iodine vacancies (VI ) and undercoordinated Pb2+ on the surface of all-inorganic perovskite films are mainly responsible for nonradiative charge recombination. An environmentally benign material, histamine (HA), is used to passivate the VI in perovskite films. A theoretical study shows that HA bonds to the VI on the surface of the perovskite film via a Lewis base-acid interaction; an additional hydrogen bond (H-bond) strengthens such interaction owing to the favorable molecular configuration of HA. Undercoordinated Pb2+ and Pb clusters are passivated, leading to significantly reduced surface trap density and prolonged charge lifetime within the perovskite films. HA passivation also induces an upward shift of the energy band edge of the perovskite layer, facilitating interfacial hole transfer. The combination of the above raises the solar cell efficiency from 19.5 to 20.8 % under 100 mW cm-2 illumination, the highest efficiency so far for inorganic metal halide perovskite solar cells (PSCs).

p-type Li, Cu-codoped NiOx hole-transporting layer for efficient planar perovskite solar cells.

p-type inorganic hole transport materials of Li, Cu-codoped NiOx films were deposited using a simple solution-based process. The as-prepared films were used as hole selective contacts for lead halide perovskite solar cell. An enhanced power conversion efficiency of 14.53% has been achieved due to the improved electrical conductivity and optical transmittance of the Li, Cu-codoped NiOx electrode interlayer.

Crystallization Control Based on the Regulation of Solvent-Perovskite Coordination for High-Performance Ambient Printable FAPbI3 Perovskite Solar Cells.

The critical requirement for ambient-printed formamidinium lead iodide (FAPbI3 ) lies in the control of nucleation-growth kinetics and defect formation behavior, which are extensively influenced by interactions between the solvent and perovskite. Here, a strategy is developed that combines a cosolvent and an additive to efficiently tailor the coordination between the solvent and perovskite. Through in situ characterizations, the direct crystallization from the sol-gel phase to α-FAPbI3 is illustrated. When the solvent exhibits strong interactions with the perovskite, the sol-gel phases cannot effectively transform into α-FAPbI3 , resulting in a lower nucleation rate and confined crystal growth directions. Consequently, it becomes challenging to fabricate high-quality void-free perovskite films. Conversely, weaker solvent-perovskite coordination promotes direct crystallization from sol-gel phases to α-FAPbI3 . This process exhibits more balanced nucleation-growth kinetics and restrains the formation of defects and microstrains in situ. This strategy leads to improved structural and optoelectronic properties within the FAPbI3 films, characterized by more compact grain stacking, smoother surface morphology, released lattice strain, and fewer defects. The ambient-printed FAPbI3 perovskite solar cells fabricated using this strategy exhibit a remarkable power conversion efficiency of 24%, with significantly reduced efficiency deviation and negligible decreases in the stabilized output.

Modifying Surface Termination by Bidentate Chelating Strategy Enables 13.77% Efficient Kesterite Solar Cells.

Surfaces display discontinuities in the kesterite-based polycrystalline films can produce large defect densities, including strained and dangling bonds. These physical defects tend to introduce electronic defects and surface states, which can greatly promote nonradiative recombination of electron-hole pairs and damage device performance. Here, an effective chelation strategy is reported to suppress these harmful physical defects related to unterminated Cu, Zn, and Sn sites by modifying the surface of Cu2ZnSn(S,Se)4 (CZTSSe) films with sodium diethyldithiocarbamate (NaDDTC). The conjoint theoretical calculations and experimental results reveal that the NaDDTC molecules can be coordinate to surface metal sites of CZTSSe films via robust bidentate chelating interactions, effectively reducing surface undercoordinated defects and passivating the electron trap states. Consequently, the solar cell efficiency of the NaDDTC-treated device is increased to as high as 13.77% under 100 mW cm-2 illumination, with significant improvement in fill factor and open-circuit voltage. This surface chelation strategy provides strong surface termination and defect passivation for further development and application of kesterite-based photovoltaics.

Manipulating the Formation of 2D/3D Heterostructure in Stable High-Performance Printable CsPbI3 Perovskite Solar Cells.

Manipulating the formation process of the 2D/3D perovskite heterostructure, including its nucleation/growth dynamics and phase transition pathway, plays a critical role in controlling the charge transport between 2D and 3D crystals, and consequently, the scalable fabrication of efficient and stable perovskite solar cells. Herein, the structural evolution and phase transition pathways of the ligand-dependent 2D perovskite atop the 3D surface are revealed using time-resolved X-ray scattering. The results show that the ligand size and shape have a critical influence on the final 2D structure. In particular, ligands with smaller sizes and more reactive sites tend to form the n = 1 phase. Increasing the ligand size and decreasing the reactive sites promote the transformation from 3D to n = 3 and n < 3 phases. These findings are useful for the rational design of the phase distribution in 2D perovskites to balance the charge transport and stability of the perovskite films. Finally, solar cells based on ambient-printed CsPbI3 with n-butylammonium iodide treatment achieve an improved efficiency of 20.33%, which is the highest reported value for printed inorganic perovskite solar cells.

Tailored Cysteine-Derived Molecular Structures toward Efficient and Stable Inorganic Perovskite Solar Cells.

Surface-defect-triggered non-radiative charge recombination and poor stability have become the main roadblock to continued improvement in inorganic perovskite solar cells (PSCs). Herein, the main culprits are identified on the inorganic perovskite surface by first-principles calculations, and to purposefully design a brand-new passivator, Boc-S-4-methoxy-benzyl-l-cysteine (BMBC), whose multiple Lewis-based functional groups (NH, S and CO) to suppress halide vacancies and coordinate with undercoordinated Pb2+ through typical Lewis baseacid reactions. The tailored electron-donating methoxyl group (CH3 O-) can cause an increased electron density on the benzene ring, which strengthens the interaction with undercoordinated Pb2+ via electrostatic interactions. This BMBC passivation can reduce the surface trap density, enlarge grains, prolong the charge lifetime, and cause a more suitable energy-level alignment. In addition, the hydrophobic tert-butyl in butoxycarbonyl (Boc-) group ensures that BMBC is uniformly covered and prevents harmful aggregation through steric repulsion at the perovskite/hole-transporting layer (HTL) interface, thus providing a hydrophobic umbrella to resist moisture invasion. Consequently, the combination of the above increases the efficiency of CsPbI3-x Brx PSC from 18.6% to 21.8%, the highest efficiency for this type of inorganic metal halide PSCs so far, as far as it is known. Moreover, the device exhibits higher environmental and thermal stability.

Ionic Liquid Treatment for Highest-Efficiency Ambient Printed Stable All-Inorganic CsPbI3 Perovskite Solar Cells.

All-inorganic cesium lead triiodide (CsPbI3 ) perovskite is well known for its unparalleled stability at high temperatures up to 500 °C and under oxidative chemical stresses. However, upscaling solar cells via ambient printing suffers from imperfect crystal quality and defects caused by uncontrollable crystallization. Here, the incorporation of a low concentration of novel ionic liquid is reported as being promising for managing defects in CsPbI3 films, interfacial energy alignment, and device stability of solar cells fabricated via ambient blade-coating. Both theoretical simulations and experimental measurements reveal that the ionic liquid successfully regulates the perovskite thin-film growth to decrease perovskite grain boundaries, strongly coordinates with the undercoordinated Pb2+ to passivate iodide vacancy defects, aligns the interface to decrease the energy barrier at the electron-transporting layer, and relaxes the lattice strain to promote phase stability. Consequently, ambient printed CsPbI3 solar cells with power conversion efficiency as high as 20.01% under 1 sun illumination (100 mW cm-2 ) and 37.24% under indoor light illumination (1000 lux, 365 µW cm-2 ) are achieved; both are the highest for printed all-inorganic cells for corresponding applications. Furthermore, the bare cells show an impressive long-term ambient stability with only ≈5% PCE degradation after 1000 h aging under ambient conditions.

Tapered Coaxial Arrays for Photon- and Plasmon-Enhanced Light Harvesting in Perovskite Solar Cells: A Theoretical Investigation Using the Finite Element Method.

Although there have been reports of separate studies of photon-enhanced and plasmon-enhanced light harvesting to improve perovskite solar cell (PSC) efficiency, there are none that have achieved simultaneous enhancement in both photonic and plasmonic effects in PSCs. In this work, we designed a layer of tapered coaxial humps (TCHs) to harvest both in PSCs. The light absorption behavior of the textured perovskite layer in PSCs was systematically investigated through the finite element method (FEM). The calculation results show that the TCH-textured perovskite layer absorbs 67.6 % of visible light under AM 1.5G solar irradiation, a 21.8 % increase relative to the planar reference cell without TCHs. Using this design, a perovskite thickness of only 106 nm is needed to realize the full light absorption that normally requires 300-nm-thick perovskite without TCHs. To reveal the mechanism of light absorption enhancement, the specific field distributions were studied. We demonstrated that different photonic modes and plasmonic modes collectively result in remarkable light absorption enhancement in the 500-800 nm wavelength range. The textured PSCs reported herein provide an effective method to decrease Pb-based perovskite consumption and realize angle-insensitive and ultrathin PSCs.

VS2 and its doped composition: Catalytic depolymerization of alkali lignin for increased bio-oil production.

VS2 spheres and VS2 sheets with doped compositions (Mo, Ag and graphite) were successfully prepared by one-step hydrothermal method and characterized by different techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption isotherms. Catalysts were applied for the depolymerization of alkali lignin. VS2 spheres exhibited lower yield of degraded lignin and bio-oil than those with VS2 sheets and VS2 flowers heated to 250 °C and held for 1.5 h with 2.0 MPa H2. The catalytic depolymerization performance was markedly affected by the dopant in the VS2 sheets, with the highest degraded lignin yield of 81.22%, achieved over 5 wt% Ag-VS2 at 290 °C under 2.0 MPa H2 for 1.5 h, yielding 61.23% bio-oil. The VS2-based catalysts show excellent selectivity in the interruption of the lignin structure and target production of bio-oil. The bio-oil showed that the relevant contents of a phenolic-type compound changes significantly according to the dopant in the VS2 catalyst.

Enhancing Grain Growth for Efficient Solution-Processed (Cu,Ag)2ZnSn(S,Se)4 Solar Cells Based on Acetate Precursor.

Material crystallinity is the overriding factor in the determination of the photoelectric properties of absorber materials and the overall performance of the photovoltaic device. Nevertheless, in the Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic device, the bilayer or trilayer structure for the absorber has been broadly observed, which is generally harmful to the cell performance because the probability of photogenerated carrier recombination at grain boundaries significantly increased. Herein, our experiment reveals that the application of anions to a new family of (Cu,Ag)2ZnSn(S,Se)4 (CAZTSSe) materials leads to an increase in grain size and crystallinity. It is inspiring that using acetate starting materials in the precursor solution, a uniform, compact, and pinhole-free CAZTS precursor film was obtained, and the smoothness of the films surpassed that of films fabricated from the oxide route. More importantly, the crystallization of the CAZTSSe film has been considerably enhanced after selenization, and large grains going through the entire absorber layer was successfully obtained. Additionally, it is observed that the Voc accompanied by excellent crystallinity improved significantly due to the pronouncedly reduced carrier recombination loss at grain boundaries. As a consequence, the power conversion efficiency (PCE) of the CAZTSSe photovoltaic device is successfully increased from 10.35% (oxide route) to 11.32% (acetate route). Importantly, our work attests to the feasibility of tuning the crystallization of the CZTSSe film by simple chemistry.

Prediction of holocellulose and lignin content of pulp wood feedstock using near infrared spectroscopy and variable selection.

Wood is the main feedstock source for pulp and paper industry. However, chemical composition variations from multispecies and multisource feedstock heavily affect the production continuity and stability. As a rapid and non-destructive analysis technique, near infrared (NIR) spectroscopy provides an alternative for wood properties on-line analysis and feedstock quality control. Herein, near infrared spectroscopy coupled with partial least squares (PLS) regression was used to predict holocellulose and lignin contents of various wood species including poplars, eucalyptus and acacias. In order to obtain more accurate and robust prediction models, a comparison was conducted among several variable selection methods for NIR spectral variables optimization, including competitive adaptive reweighted sampling (CARS), Monte Carlo-uninformative variable elimination (MC-UVE), successive projections algorithm (SPA), and genetic algorithm (GA). The results indicated that CARS method displayed relatively higher efficiency over other methods in elimination of uninformative variables as well as enhancement of the predictive performance of models. CARS-PLS models showed significantly higher robustness and accuracy for each property using lowest variable numbers in cross validation and external validation, demonstrating its applicability and reliability for prediction of multispecies feedstock properties.

ZnO nanotubes supported molecularly imprinted polymers arrays as sensing materials for electrochemical detection of dopamine.

In this study, ZnO nanotubes (ZNTs) were prepared onto fluorine-doped tin oxide (FTO) glass and used as supports for MIPs arrays fabrication. Due to the imprinted cavities are always located at both inner and outer surface of ZNTs, these ZNTs supported MIPs arrays have good accessibility towards template and can be used as sensing materials for chemical sensors with high sensitivity, excellent selectivity and fast response. Using K3[Fe(CN)6] as electron probe, the fabricated electrochemical sensor shows two linear dynamic ranges (0.02-5µM and 10-800µM) towards dopamine. This proposed electrochemical sensor has been applied for dopamine determination with satisfied recoveries and precision. More complex human urine samples also confirmed that the proposed method has good accuracy for dopamine determination in real biological samples. These results suggest potential applicability of the proposed method and sensor in important molecule analysis.

Elemental Precursor Solution Processed (Cu1-xAgx)2ZnSn(S,Se)4 Photovoltaic Devices with over 10% Efficiency.

The partial substitution of Cu+ with Ag+ into the host lattice of Cu2ZnSn(S,Se)4 thin films can reduce the open-circuit voltage deficit (Voc,deficit) of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. In this paper, elemental Cu, Ag, Zn, Sn, S, and Se powders were dissolved in solvent mixture of 1,2-ethanedithiol (edtH2) and 1,2-ethylenediamine (en) and used for the formation of (Cu1-xAgx)2ZnSn(S,Se)4 (CAZTSSe) thin films with different Ag/(Ag + Cu) ratios. The key feature of this approach is that the impurity atoms can be absolutely excluded. Further results indicate that the variations of grain size, band gap, and depletion width of the CAZTSSe layer are generally determined by Ag substitution content. Benefiting from the Voc enhancement (∼50 mV), the power conversion efficiency is successfully increased from 7.39% (x = 0) to 10.36% (x = 3%), which is the highest efficiency of Ag substituted devices so far.

Solution-processed highly efficient Cu2ZnSnSe4 thin film solar cells by dissolution of elemental Cu, Zn, Sn, and Se powders.

Solution deposition approaches play an important role in reducing the manufacturing cost of Cu2ZnSnSe4 (CZTSe) thin film solar cells. Here, we present a novel precursor-based solution approach to fabricate highly efficient CZTSe solar cells. In this approach, low-cost elemental Cu, Zn, Sn, and Se powders were simultaneously dissolved in the solution of thioglycolic acid and ethanolamine, forming a homogeneous CZTSe precursor solution to deposit CZTSe nanocrystal thin films. Based on high-quality CZTSe absorber layer, pure selenide CZTSe solar cell with a photoelectric conversion efficiency of 8.02% has been achieved without antireflection coating.

Fabrication of Cu2ZnSn(S,Se)4 solar cells via an ethanol-based sol-gel route using SnS2 as Sn source.

Cu2ZnSn(S,Se)4 semiconductor is a promising absorber layer material in thin film solar cells due to its own virtues. In this work, high quality Cu2ZnSn(S,Se)4 thin films have been successfully fabricated by an ethanol-based sol-gel approach. Different from those conventional sol-gel approaches, SnS2 was used as the tin source to replace the most commonly used SnCl2 in order to avoid the possible chlorine contamination. In addition, sodium was found to improve the short-circuit current and fill factor rather than the open-circuit voltage due to the decrease of the thickness of small-grained layer. The selenized Cu2ZnSn(S,Se)4 thin films showed large densely packed grains and smooth surface morphology, and a power conversion efficiency of 6.52% has been realized for Cu2ZnSn(S,Se)4 thin film solar cell without antireflective coating.