Solvent Engineering Method Research Articles

A facile strategy for highly efficient perovskite crystals fabricated in a high moisture environment via solvent engineering process

BackgroundHybrid organic perovskite solar cells (PSCs) have recently gained recognition for their excellent photovoltaic properties. However, most PSCs were fabricated in a nitrogen-filled glovebox to prevent damage from moisture. Overcoming humidity damage is crucial for PSC fabrication in an ambient atmosphere. Fabricating perovskite solar cells (PSCs) under ambient atmosphere conditions needs the aid of substrate heating or air-knife flow to rapidly evaporate solvents. MethodsHerein, we propose a facile solvent engineering method without extra equipment or processes for fabricating highly efficient PSCs in a high moisture condition by a one-step spin-coating process. Acetone incorporation into the perovskite precursor solution not only prevents the ingress of moisture, but also accelerates the volatilization of solvents during the crystallization process. Significant findingsThe as-prepared PSCs feature low trap-state density, high charge recombination resistance, low hysteresis, and long charge lifetime. Little MABr and PbBr2 are separated out to passivate interface/grain-boundary defects. At a 10% acetone incorporation, the highest power conversion efficiency can reach 17.75% for the PSC fabricated in 70% relative humidity. The work provides a facile, promising method to prepare highly efficient PSCs in an ambient atmosphere.

Improved Stability and Catalytic Efficiency of ω-Transaminase in Aqueous Mixture of Deep Eutectic Solvents.

The efficient biosynthesis of chiral amines at an industrial scale to meet the high demand from industries that require chiral amines as precursors is challenging due to the poor stability and low catalytic efficiency of ω-transaminases (ω-TAs). Herein, this study adopted a green and efficient solvent engineering method to explore the effects of various aqueous solutions of deep eutectic solvents (DESs) as cosolvents on the catalytic efficiency and stability of ω-TA. Binary- and ternary-based DESs were used as cosolvents in enhancing the catalytic activity and stability of a ω-TA variant from Aspergillus terreus (E133A). The enzyme exhibited a higher catalytic activity in a ternary-based DES that was 2.4-fold higher than in conventional buffer. Moreover, the thermal stability was enhanced by a magnitude of 2.7, with an improvement in storage stability. Molecular docking studies illustrated that the most potent DES established strong hydrogen bond interactions with the enzyme's amino acid, which enhanced the catalytic efficiency and improved the stability of the ω-TA. Molecular docking is essential in designing DESs for a specific enzyme.

Solvent-antisolvent interactions in metal halide perovskites.

The fabrication of metal halide perovskite films using the solvent-engineering method is increasingly common. In this method, the crystallisation of the perovskite layer is triggered by the application of an antisolvent during the spin-coating of a perovskite precursor solution. Herein, we introduce the current state of understanding of the processes involved in the crystallisation of perovskite layers formed by solvent engineering, focusing in particular on the role of antisolvent properties and solvent-antisolvent interactions. By considering the impact of the Hansen solubility parameters, we propose guidelines for selecting the appropriate antisolvent and outline open questions and future research directions for the fabrication of perovskite films by this method.

Solvent Engineering Approach Toward Optimized Phase and Morphology of CsPbBr3 Films for Efficient and Stable Planar Perovskite Solar Cells and Photodetectors

All‐inorganic perovskite CsPbBr3 has drawn a lot of interest as an active layer applied in photovoltaics due to its outstanding stability in ambient air. However, the procedure of preparing high‐quality CsPbBr3 films still remains a serious challenge because of the tedious process and toxic solvent. Herein, a solvent engineering method that involves green solvent with mixed H2O/C2H5OH to dissolve CsBr is presented to produce all‐inorganic perovskite CsPbBr3 films. CsPbBr3 perovskite solar cells (PSCs) are fabricated based on planar n‐i‐p structure. Compared with CsBr H2O solution, the CsPbBr3 films with optimized mixed solvent method exhibit larger grain size and improved crystallinity. As a result, the carbon‐electrode PSCs based on the mixed solvent method exhibit an increased efficiency of 9.70%. The best‐performing device retains 96.95% of the initial power conversion efficiency (PCE) after storing 1000 h under ambient air and 86.46% of the initial PCE after continuous illumination for 100 min. Moreover, the photodetector based on the same structure as the CsPbBr3 device shows high responsivity and high detectivity. The result not only provides an easy and straightforward method to prepare the uniform and pinhole‐free CsPbBr3 films, but also reduces the toxicity of the CsBr solution used to make the CsPbBr3 PSCs.

Stable and Bright Electroluminescent Devices utilizing Emissive 0D Perovskite Nanocrystals Incorporated in a 3D CsPbBr3 Matrix.

The 0D cesium lead halide perovskite Cs4 PbBr6 has drawn remarkable interest due to its highly efficient robust green emission compared to its 3D CsPbBr3 counterpart. However, seizing the advantages of the superior photoluminescence properties for practical light-emitting devices remains elusive. To date, Cs4 PbBr6 has been employed only as a higher-bandgap nonluminescent matrix to passivate or provide quantum/dielectric confinement to CsPbBr3 in light-emitting devices and to enhance its photo-/thermal/environmental stability. To resolve this disparity, a novel solvent engineering method to incorporate highly luminescent 0D Cs4 PbBr6 nanocrystals (perovskite nanocrystals (PNCs)) into a 3D CsPbBr3 film, forming the active emissive layer in single-layer perovskite light-emitting electrochemical cells (PeLECs) is designed. A dramatic increase of the maximum external quantum efficiency and luminance from 2.7% and 6050cd m-2 for a 3D-only PeLEC to 8.3% and 11 200cd m-2 for a 3D-0D PNC device with only 7% by weight of 0D PNCs is observed. The majority of this increase is driven by the efficient inherent emission of the 0D PNCs, while the concomitant morphology improvement also contributes to reduced leakage current, reduced hysteresis, and enhanced operational lifetime (half-life of 129 h), making this one of the best-performing LECs reported to date.

Synthesis of (CH3NH3)2CuCl4 nanoparticles by antisolvent engineering

Improving the performance of devices while avoiding Pb toxicity is one of the most difficult challenges in perovskite-based optoelectronic technology. Here, the solvent engineering method was employed to synthesize Cu-based organic–inorganic perovskite. The X-ray diffraction showed the monoclinic phase of the perovskites and different approximations verified the nanocrystalline structure. Scanning electron microscopy shows grain size varying between 40 nm and 110 nm with an average grain size of 72 nm. The perovskite showed a fine absorption with a bandgap of 2.38 eV, suitable for visible light absorption.

Solvent Engineering for Controlled Crystallization and Growth of All-Inorganic Pb-Free Rudorffite Absorbers of Perovskite Solar Cells.

Solution-processed Ag-Bi-I rudorffites with direct band gaps of <2 eV show promise for highly efficient and cost-effective Pb-free solar cells. However, relatively fast crystallization rates of Bi-based films and limited solubility of BiI3 in many solvents result in poor film morphologies, inhibiting their device performance. Here, we conduct a solvent-engineering method to adjust the dynamics of nucleation and growth during film formation. We fabricate Ag2BiI5, AgBiI4, and AgBi2I7 absorber layers using a mixed solvent of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) and find that a volume percentage of 50% DMSO causes highly uniform and dense perovskite films via a BiI3-DMSO-AgI intermediate phase formation, leading to solar cells with an improved power conversion efficiency of 0.62% for the Ag2BiI5 absorber. These results provide valuable insights into the optimization of the solution processing technique to realize low-toxicity and efficient perovskite solar cells.

Crystal stabilization of α-FAPbI3 perovskite by rapid annealing method in industrial scale

Organic-inorganic hybrid formamidinium lead iodide (FAPbI3) perovskite has shown tremendous attention in recently developed photovoltaics and optelectronic devices. However, it suffers from structural instability complications, particularly the spontaneous phase transition from a dark color photoactive perovskite phase (α-FAPbI3) to a yellow color photo-inactive phase (δ-FAPbI3) at room temperature. To stabilize the photoactive α-FAPbI3, several methods were employed, including compositional engineering, 2D layer deposition on the surface, and solvent engineering method. In this communication, we have proposed a facile sequential rapid annealing method to produce the photoactive α-FAPbI3 perovskite on an industrial scale, which is highly stable at room temperature. The structural, morphological, compositional, and optical properties of the perovskite were studied using X-ray diffraction (XRD), UV–visible absorption, Laser Raman, thermogravimetric analysis (TGA), and field emission electron microscopy with elemental analysis (FE-SEM & EDAX). The strong characteristic diffraction peaks of cubic structure in XRD showed the proposed additives free preparation method is more adaptable for the preparation of high quality α-FAPbI3 perovskite for optoelectronic applications.

A High Seebeck Voltage Thermoelectric Module with P‐type and N‐type MAPbI3 Perovskite Single Crystals

AbstractIn recent years, organic–inorganic hybrid halide perovskite materials have been found to have low thermal conductivity and a large Seebeck effect, giving them great potential for thermoelectric applications. More stable single crystals make this possible. In this work, high‐quality MAPbI3 single crystals are prepared using a modified solvent engineering method, and their trap density is as low as 2.5 × 109 cm−3. It is noticed that the reaction between the crystal a metal electrode causes different degrees of doping effect along the vertical direction, leading to an increase in the intrinsic P‐type with Au metal, and forming N‐type semiconductor characteristics with Ag metal. A high Seebeck voltage thermoelectric module is obtained by combining the perovskite single crystal with different conductive characteristics. After device optimization, the thermoelectric potential of the champion module reaches a high voltage of 337 mV at 115 °C, the maximum output power with load reaches about 30 nW, and the theoretical maximum power reaches 65 nW. It is hoped that this research can promote the development of low thermal conductivity perovskite materials in the thermoelectric field.

Solvent engineering of lead-free bismuth-based perovskite material for potential application of solar cell

In the past few years, hybrid organic–inorganic perovskite materials have attracted great attention due to their impressive properties for solar cells applications. However, perovskite methylammonium lead halide is facing with toxicity issues that may hinder the wide range application of the lead halide-based hybrid perovskite solar cells. The sources of toxicity of these solar cells are the pollution from the B-site of lead ion and the toxic solvents used in the fabricating the devices. Thus, environmentally friendly materials and non-toxic solvents are highly desired for large-scale manufacturing of perovskite solar cells. In this work, the chemical and optical properties of lead-free bismuth based MA3Bi2I9 perovskite fabricated using different compositions of non-toxic solvents are investigated through solvent engineering method. Dimethyl sulfoxide (DMSO) /acetonitrile (ACN) /methyl-acetate (MA) solvents were employed as non-toxic solvent systems for the formation of homogeneous and good quality perovskite film. Hybrid organic–inorganic lead-free perovskite films were fabricated by mixing 1:1 M ratio compositions of CH3NH3I and BiI3 in different mixture of the solvents. The results show that the mixing solvent DMSO / ACN / MA at a volume ratio of 5:2:3 v / v, which incorporates the advantages of each solvent, has the best result among others. It is believed that by optimizing the solvent compositions, high performance lead-free bismuth-based perovskite film using non-toxic solvents could be obtained for potential solar cells application.

A universal method for hysteresis-free and stable perovskite solar cells using water pre-treatment

The power conversion efficiency (PCE) of organic–inorganic hybrid perovskite solar cells (PSCs) with SnO2 as an electron transport layer, achieve over 25%. However, the long-term stability and reduction of hysteresis are still great challenges. To solve these problems, different from the traditional treatment on ITO by UV or ozone, we introduce a simple, clean solvent engineering method of water spin-coating in the preparation of the SnO2 layer to obtain a compact and highly uniform SnO2 film. It is confirmed that after water treatment, the interface defects of the perovskite film are greatly reduced, and the electron transportation is also accelerated due to the near-perfect SnO2 layer. As a result, an improved PCE above 19% is obtained with triple cation (Cs/FA/MA)-mixed PSCs compared with ~16% PCE of the controlled devices. More importantly, the initial PCE of unwrapped PSCs with the water treatment can maintain 90% of their initial efficiency after exposure to ambient conditions for 360 h, while, the PSCs based on a conventional spin-coated SnO2 film degrade ~30%. Therefore, it is believe that this water spin-coating pre-treatment on SnO2 film we introduced can be a valid and practical method to obtain high-performance PSCs based on SnO2.

Electrodeposition, solvent engineering, and two-step solution deposition of the perovskite films: morphological and structural study

Perovskite solar cells are still soaring in the science and technology world. For reaching efficient solar cells, the deposition method of perovskite highly matters. It severely affects the morphological structure and grain/crystal size of the deposited film which are very crucial factors. In this work, the solvent engineering, two-step solution deposition, and electrodeposition methods have been compared and studied morphologically. While substrate plays an important role in the quality of the deposited film, experiments have been carried out on both planar and mesopore $$\text {TiO}_2$$ substrates. An image processing tool has been designed for quantitative surface analysis of the perovskite layers. The obtained results showed that the electrodeposition synthesis method on the mesopore substrate leads to an average of 99% surface coverage and the largest grain sizes (340.4 nm). It was demonstrated that the electrodeposited perovskite films had an average crystallite size of 39.11 nm which is slightly better than the other two methods. However, the solvent engineering method resulted in the most uniformity in grain sizes (standard deviation of 31.9 nm) for planar and (34.7 nm) for mesopore $$\text {TiO}_2$$ substrates. According to the presented results, the electrodeposition seems to be the method of choice for perovskite deposition for solar applications.

Barium doping effect on the photovoltaic performance and stability of MA0.4FA0.6BaxPb1-xIyCl3-y perovskite solar cells

Perovskite solar cells (PSCs) have earned widespread attention owing to its fast-growing power conversion efficiency (PCE). However, there are some challenges for this type of solar cells. The toxicity issue, current density-voltage (J-V) hysteresis, and uncertain stability hinder commercialization. In this study, we developed the PSCs with MA0.4FA0.6BaxPb1-xIyCl3-y film as active layer. The MA0.4FA0.6BaxPb1-xIyCl3-y film with various barium doping concentrations were fabricated by solvent engineering method. We investigate the surface morphology, crystal orientation, and optical property of various perovskite films. Furthermore, the in situ grazing-incidence wide-angle X-ray scattering (in-situ GIWAXS) is used to analyze the heating crystallization process of perovskite film. We discover that Ba can improve crystallinity and structural stability. For the optimal 5.0 mol% Ba replacement, the PCE of perovskite device is increased to 17.4%, the J-V hysteresis can be completely eliminated and the device demonstrates long-term stability.

CsI‐Antisolvent Adduct Formation in All‐Inorganic Metal Halide Perovskites

AbstractThe excellent optoelectronic properties demonstrated by hybrid organic/inorganic metal halide perovskites are all predicated on precisely controlling the exact nucleation and crystallization dynamics that occur during film formation. In general, high‐performance thin films are obtained by a method commonly called solvent engineering (or antisolvent quench) processing. The solvent engineering method removes excess solvent, but importantly leaves behind solvent that forms chemical adducts with the lead‐halide precursor salts. These adduct‐based precursor phases control nucleation and the growth of the polycrystalline domains. There has not yet been a comprehensive study comparing the various antisolvents used in different perovskite compositions containing cesium. In addition, there have been no reports of solvent engineering for high efficiency in all‐inorganic perovskites such as CsPbI3. In this work, inorganic perovskite composition CsPbI3 is specifically targeted and unique adducts formed between CsI and precursor solvents and antisolvents are found that have not been observed for other A‐site cation salts. These CsI adducts control nucleation more so than the PbI2–dimethyl sulfoxide (DMSO) adduct and demonstrate how the A‐site plays a significant role in crystallization. The use of methyl acetate (MeOAc) in this solvent engineering approach dictates crystallization through the formation of a CsI–MeOAc adduct and results in solar cells with a power conversion efficiency of 14.4%.

Efficient Anti-solvent-free Spin-Coated and Printed Sn-Perovskite Solar Cells with Crystal-Based Precursor Solutions

Summary Tin-based perovskite solar cells (PSCs), with more consummate optical band gaps, lower exciton-binding energies, and higher charge-carrier mobility, have not attracted tremendous research efforts compared with the lead-based ones that have a record power conversion efficiency (PCE) of 24.2%. The major challenges for Sn-based research are significantly low open-circuit voltage, poor reproducibility, and environmental instability. It has been identified that the oxidation processes take place during the preparation of precursor solutions and fabrication of films, due to the low redox potential of the stannous absorption layer. Herein, we propose two strategies of crystal-resolving and recrystallization technology to reduce the oxidation process. As a result, PCEs of 8.9% (active area of 0.04 cm2) and 5.5% (active area = 1.01 cm2) are attained using the inverted p-i-n structure, which will lead to a revival of lead-free PSC research.

Solution-Processable Unsymmetrical Triarylamines: Towards High Mobility and ON/OFF Ratio in Bottom-Gated OFETs.

Self-assembly of organic small molecules into an ordered thin film has been the key strategy towards efficient charge transport for organic field-effect transistors (OFETs). Solution processing is a feasible and economic way to enhance pi-pi interaction. Herein, nitrile-substituted unsymmetrical triarylamines for OFET applications with high mobility are reported. The compounds were constructed by Suzuki cross-coupling reactions under inert conditions. The HOMO level of about 5.3 eV indicates good hole-transporting ability. OFETs were assembled in bottom-gate, top-contact architecture. Devices fabricated from a binary solvent system exhibited excellent p-channel characteristics, with impressively high charge-carrier mobility of up to 2.58 cm2 V-1 s-1 and ION/OFF current ratios of 106 -107 . SEM and AFM analysis showed the efficient molecular self-assembly attained by the simple and effective solvent-engineering method. Theoretical insights obtained by DFT calculations supported by single-crystal structures showed that the crystalline nature and packing modes of these compounds ensure high mobility. The results prove that these compounds have great potential for use in numerous electronic applications, such as sensors and logic switches.

Simple Solvent Engineering for High-Mobility and Thermally Robust Conjugated Polymer Nanowire Field-Effect Transistors

Electron donor (D)-acceptor (A)-type conjugated polymers (CPs) have emerged as promising semiconductor candidates for organic field-effect transistors. Despite their high charge carrier mobilities, optimization of electrical properties of D-A-type CPs generally suffers from complicated post-deposition treatments such as high-temperature thermal annealing or solvent-vapor annealing. In this work, we report a high-mobility diketopyrrolopyrrole-based D-A-type CP nanowires, self-assembled by a simple but very effective solvent engineering method that requires no additional processes after film deposition. In situ grown uniform nanowires at room temperature were shown to possess distinct edge-on chain orientation that is beneficial for lateral charge transport between source and drain electrodes in FETs. FETs based on the polymer nanowire networks exhibit impressive hole mobility of up to 4.0 cm2 V-1 s-1. Moreover, nanowire FETs showed excellent operational stability in high temperature up to 200 °C because of the strong interchain interaction and alignment.

Study of the Crystallization of Metal Halide Perovskites Containing Additives via Differential Scanning Calorimetry

Control of the crystallization and morphology has been one of the major challenges in the design and fabrication of perovskite thin films. Recently, additives of different nature have been used to improve the crystallization and the quality of perovskite films. In this work, we study in detail the role of water (H2O), 1,8-diiodooctane (DIO), and dimethylsulfoxide (DMSO) as additives in the precursor solution of the CH3NH3PbI3−xClx perovskite. Differential scanning calorimetry analysis revealed the thermal transitions for the crystallization of CH3NH3PbI3−xClx perovskite depending on the chemical nature and physical properties of the additive. Information from thermograms enabled us to find optimal annealing ramps for each additive. We found that DIO produced changes mainly due to the interaction of this additive with the precursor salts in solution, while H2O due to its different boiling point compared to the DMF solvent. DMSO dramatically modified the thermal transitions to higher temperatures; however, high quality films were obtained only when the solvent engineering method is used.

A Two-Stage Annealing Strategy for Crystallization Control of CH3 NH3 PbI3 Films toward Highly Reproducible Perovskite Solar Cells.

The solvent-engineering method is widely used to fabricate top-performing perovskite solar cells, which, however, usually exhibit inferior reproducibility. Herein, a two-stage annealing (TSA) strategy is demonstrated for processing of perovskite films, namely, annealing the intermediate phase at 60 °C for the first stage then at 100 °C for the second stage. Compared to conventional direct annealing temperature (DHA) at 100 °C, using this strategy, MAPbI3 films become more controllable, leading to superior film uniformity and device reproducibility with the champion device efficiency reaching 19.8%. More specifically, the coefficient of variation of efficiency for 49 cells is reduced to 5.9%, compared to 9.8% for that using DHA. The TSA process is carefully studied using Fourier transform infrared spectroscopy, X-ray diffraction, and UV-vis absorption spectroscopy. It is found that in comparison with DHA the formation of hydrogen bonding and crystallization of perovskite are much slower and can be better controlled when using TSA. The improvements in film uniformity and device reproducibility are attributed to: 1) controllable MAPbI3 crystal growth stemming from the progressive formation of hydrogen bonding between methylammonium and halide; 2) suppression of intermediate phase film dewetting, which is believed to be due to its decreased mobility at the initial low-temperature annealing stage.

Study of carbon-based hole-conductor-free perovskite solar cells

In this paper, the perovskite solar cells (PSCs) with the structure of FTO glass/compact TiO2/mesoporous TiO2/CH3NH3PbI3/carbon electrode were designed and fabricated. The CH3NH3PbI3 absorption layers were prepared using one-step solvent-engineering method. The effects of volume ratios of dimethyl sulfoxide (DMSO) to N, N-dimethylformamide (DMF) and molar ratios of PbI2 to CH3NH3I (MAI) on structure and morphology of CH3NH3PbI3 absorption layers, as well as photovoltaic performance of PSCs were studied. The results show that the PSCs based on a specific ratio of PbI2:MAI = 1:1.4 and DMSO:DMF = 1:3 exhibited an optimal photovoltaic performance, yielding an open-circuit voltage (Voc) of 0.72 V, short-circuit current density (Jsc) of 25.98 mA/cm2, fill factor (FF) of 0.46, and power conversion efficiency (PCE) of 8.45%. And the incident photon-to-electron conversion efficiency (IPCE) is close to 85% between 400 and 600 nm visible region.