Sequential Deposition Process Research Articles

Interfacial competing interaction eliminates voids in the buried interface for efficient and stable perovskite solar modules on bare NiOX

Perovskite solar cells (PSCs) with impressive efficiency is promising for commercialization. However, when scaling up PSCs to large-area perovskite solar modules (PSMs), the rapid degradation of performance and stability still remains a grand challenge. One of the main causes of the degradation is the presence of local voids in the buried interface for large-area films, which we find could be attributed to the unbalanced interfacial interaction between precursor solvent and substrate. Here we improve a scalable and low-temperature sequential two-step chemical bath deposition process aiming for high quality NiOX. Further with the modulation of A-site cations to enhance the interaction between DMSO and perovskite precursor, the potential for DMSO absorbing on the NiOX could be eliminated. This strategy can inhibit the delay movement of DMSO on NiOX and improve the buried interfacial quality, with compact morphology and absent of voids. The inverted structured PSCs and PSMs based on the bare NiOX and modified perovskite precursor reach a champion efficiency of 22.40% and 19.09%, respectively, which are both among the highest reported values. The highly efficient PSMs also exhibit a long-term operational stability, which retain 84% of the initial performance after 1056 h operating under one-sun illumination.

High-Efficiency Ternary Polymer Solar Cells with a Gradient-Blended Structure Fabricated by Sequential Deposition.

Acquiring the ideal blend morphology of the active layer to optimize charge separation and collection is a constant goal of polymer solar cells (PSCs). In this paper, the ternary strategy and the sequential deposition process were combined to make sufficient use of the solar spectrum, optimize the energy-level structure, regulate the vertical phase separation morphology, and ultimately enhance the power conversion efficiency (PCE) and stability of the PSCs. Specifically, the donor and acceptor illustrated a gradient-blended distribution in the sequential deposition-processed films, thus resulting in facilitated carrier characteristics in the gradient-blended devices. Consequently, the PSCs based on D18-Cl/Y6:ZY-4Cl have achieved a device efficiency of over 18% with the synergetic improvement of open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF). Therefore, this work reveals a facile approach to fabricating PSCs with improved performance and stability.

Achieving Desired Pseudo-Planar Heterojunction Organic Solar Cells via Binary-Dilution Strategy.

The sequential deposition process has demonstrated the great possibility to achieve a photolayer architecture with an ideal gradient phase separation morphology, which has a vital influence on the physical processes that determine the performance of organic solar cells (OSCs). However, the controllable preparation of pseudo-planar heterojunction (P-PHJ) with gradient distribution has not been effectively elucidated. Herein, a binary-dilution strategy is proposed, the PM6 solution with micro acceptor BO-4Cl and the L8-BO solution with micro donor PM6 respectively, to form P-PHJ film. This architecture exists good donor (D) and acceptor (A) vertical gradient distribution and larger D/A interpenetrating regions, which promotes exciton generation and dissociation, shortens charge transport distance and optimizes carrier dynamics. Moreover, the dilution of PM6 by BO-4Cl promotes the regulation of active layer aggregation size and phase purity, thus alleviating energy disorder and voltage loss. As a result, the P-PHJ device exhibits an outstanding power conversion efficiency of 19.32% with an excellent short-circuit current density of 26.92mA cm-2 , much higher than planar binary heterojunction (17.67%) and ternary bulk heterojunction (18.49%) devices. This research proves a simple but effective method to provide an avenue for constructing desirable active layer morphology and high-performance OSCs.

MACl-Induced Controlled Crystallization in Sequentially Deposited Perovskites for High-Efficiency and Stable Perovskite Solar Cells

Perovskite solar cells are attracting more and more attention due to their higher absorption and low cost. However, fabricating the perovskite film with high crystallinity and ideal morphology, which presents large-size and uniform particles with fewer grain boundaries, still needs further improvement. Herein, we introduce MAPbCl3 crystals into the PbI2 film in the sequential deposition process, which obtained the controlled crystallization in perovskite films. The perovskite films induced by MAPbCl3 have stronger crystallinity, fewer defect states, and larger grain size, reducing carrier recombination and improving carrier transfer. The optimized perovskite solar cell (PSC) has achieved a power conversion efficiency of 20.97%. Furthermore, the stability of PSCs has also been enhanced due to the reduced grain boundaries impeding moisture diffusion. This strategy can be applied in other solution-based fabrication processes to improve the photovoltaic performance of PSCs.

Spectrum‐Selective High‐Temperature Tolerant Thermal Emitter by Dual‐Coherence Enhanced Absorption for Solar Thermophotovoltaics

AbstractSolar thermophotovoltaics (STPV) receive considerable attention for the record high energy transfer efficiency beyond conventional photovoltaics systems, which requires a well‐designed structured absorber/emitter and high operating temperature. However, the inherent tradeoff between increased operation temperature and material/structure stability (especially for the thermal emitters) severely hinders the development of STPV. In this work, a new design is proposed for a step‐function‐like thermal emitter based on a two‐path (quasi) coherent perfect absorption effect, which is experimentally enabled by a few‐layer Si/Mo/AlN lamellar film on a Mo substrate through a sequential physical vapor deposition process. The as‐prepared lamellar emitter exhibits maximal emissivity of ≈97% for 1.4 µm with excellent thermal suppression down to 10% across 3.4–10 µm, the performance of which is well maintained up to 973 K. When employed in the established STPV system, the dual coherent enhanced absorption (DCEA) system contributes to an increase of 20% in the total system efficiency compared to the unimodal coherent perfect absorption counterpart. The design proposed in this study provides a new methodology for improving the efficiency of the STPV system and may have significant applications in improving thermal energy regulation for compact systems.

Novel Diffusion‐Regulated Layering Methodology to Improve Blend Miscibility and Thermal Stability of Organic Photovoltaics

AbstractExtensive research on bulk‐heterojunction (BHJ) optimization has advanced organic photovoltaics (OPVs). However, the need for research addressing the issue of morphological instability and ensuring long‐term durability remains a priority. Herein, a diffusion‐governed morphological modification methodology via a sequential deposition (SD) process comprising ternary components with low miscibility is demonstrated. Sequential coating of a high glass transition temperature (Tg) material and a host binary blend induces a concentration difference between successively coated layers, allowing for effective blending of immiscible materials during solvent evaporation. The enhanced miscibility of the SD‐processed BHJ layer facilitates molecular interactions between the high Tg material and the host materials, thereby increasing the Tg of the BHJ blend. The SD‐processed OPVs exhibit superior photovoltaic performance and suppressed glass transition under thermal stress compared to reference OPVs fabricated via a conventional method. After 500 h of thermal aging at 85 °C, the SD‐BHJ OPV retains over 80% of its initial efficiency, whereas the reference device shows a drastic drop to below 80% of its initial efficiency after only 80 h. This study provides a step toward efficient, long‐term stable OPVs by overcoming the limitations of blend miscibility and poor thermal durability of conventional BHJ systems via a SD process.

Multifunctional Metal-organic Frameworks Capsules Modulate Reactivity of Lead Iodide toward Efficient Perovskite Solar Cells with Ultraviolet Resistance.

The two-step sequential deposition process is demonstrated as a reliable technology for the fabrication of efficient perovskite solar cells (PVSCs). However, the complete conversion of dense PbI2 to perovskite in planar PVSCs is tough without mesoporous titanium dioxide as support. Herein, multifunctional capsules consisting of zeolitic imidazolate framework-8 (ZIF-8) encapsulant and formamidinium iodide (FAI) are introduced between tin oxide (SnO2 ) and lead iodide (PbI2 ) layer. Intriguingly, the capsule dopant interlayer benefits the formation of porous PbI2 film due to the porous nanostructure of ZIF-8 which is favorable for the subsequent intercalation reaction. Furthermore, the constituent of the perovskite precursor in ZIF-8 pores can convert into the crystal nuclei of perovskite by reacting with PbI2 first, thereby promoting further perovskite crystallization. Significantly, the incorporation of ZIF-8 can enhance the resistance of perovskite against ultraviolet (UV) illumination due to down-conversion effect. Consequently, the modified device achieves a champion power conversion efficiency (PCE) of 24.08% and displays enhanced UV stability, which can sustain 83% of its original PCE under 365nm UV illumination for 300h. Moreover, the unencapsulated device maintains 90% of initial PCE after 1500h storage in dark ambient conditions with a relative humidity range of 50∼70%. This article is protected by copyright. All rights reserved.

Optimizing the morphology of all-polymer solar cells for enhanced photovoltaic performance and thermal stability

Due to the complicated film formation kinetics, morphology control remains a major challenge for the development of efficient and stable all-polymer solar cells (all-PSCs). To overcome this obstacle, the sequential deposition method is used to fabricate the photoactive layers of all-PSCs comprising a polymer donor PTzBI-oF and a polymer acceptor PS1. The film morphology can be manipulated by incorporating amounts of a dibenzyl ether additive into the PS1 layer. Detailed morphology investigations by grazing incidence wide-angle X-ray scattering and a transmission electron microscope reveal that the combination merits of sequential deposition and DBE additive can render favorable crystalline properties as well as phase separation for PTzBI-oF:PS1 blends. Consequently, the optimized all-PSCs delivered an enhanced power conversion efficiency (PCE) of 15.21% along with improved carrier extraction and suppressed charge recombination. More importantly, the optimized all-PSCs remain over 90% of their initial PCEs under continuous thermal stress at 65 °C for over 500 h. This work validates that control over microstructure morphology via a sequential deposition process is a promising strategy for fabricating highly efficient and stable all-PSCs.

Polymer‐Assisted Heterogeneous Lead Iodide in a Two‐Step Process: Fabrication of Efficient and Stable Perovskite Solar Cells

Developing pinhole‐free, superior crystal, and high‐quality perovskite films by regulating the lead iodide microstructure in two‐step sequential deposition has attracted increased interest in the domain of perovskite solar cells (PSCs) for commercial applications. Herein, a multifunctional polymer, polyvinyl alcohol (PVA), is incorporated into a two‐step sequential deposition process to regulate morphological transform of PbI2 and then the high‐quality perovskite films are obtained. PVA as a scaffold combines with uncoordinated Pb2+ in the PbI2 precursor solution through a strong Pb–O interaction, leading to rough PbI2. In the second step, the uneven and heterogeneous PbI2 allows FA&MA permeation and then drives adequate coordination reactions between PbI64− octahedron and bulky cations. Furthermore, the PVA gathering at grain boundary passivates redundant Pb2+ by the PbO bonding interactions in the final polycrystalline films. Consequently, high‐quality (FAPbI3)0.90(MAPbBr3)0.10 perovskite layers are obtained with promoted crystal growth, inhibited voids formation/delamination, and thus reduced trap states. The universality and versatility of this strategy not only enables improved power conversion efficiencies of 22.81% (Ag‐based devices) and 16.58% (carbon‐based devices) across architectures but also remarkedly enhances the device stability in ambient‐air aging condition, which delivers a facile and broadly applicable additive synergetic strategy for efficient and stable PSCs.

Control of the Crystallization and Phase Separation Kinetics in Sequential Blade‐Coated Organic Solar Cells by Optimizing the Upper Layer Processing Solvent

AbstractSequential deposition of the active layer in organic solar cells (OSCs) is favorable to circumvent the existing drawbacks associated with controlling the microstructure in bulk‐heterojunction (BHJ) device fabrication. However, how the processing solvents impact on the morphology during sequential deposition processes is still poorly understood. Herein, high‐efficiency OSCs are fabricated by a sequential blade coating (SBC) through optimization of the morphology evolution process induced by processing solvents. It is demonstrated that the device performance is highly dependent on the processing solvent of the upper layer. In situ morphology characterizations reveal that an obvious liquid–solid phase separation can be identified during the chlorobenzene processing of the D18 layer, corresponding to larger phase separation. During chloroform (CF) processing of the D18 layer, a proper aggregation rate of Y6 and favorable intermixing of lower and upper layers results in the enhanced crystallinity of the acceptor. This facilitates efficient exciton dissociation and charge transport with an inhibited charge recombination in the D18/CF‐based devices, contributing to a superior performance of 17.23%. These results highlight the importance of the processing solvent for the upper layer in the SBC strategy and suggest the great potential of achieving optimized morphology and high‐efficiency OSCs using the SBC strategy.

The Role of Ionic Liquids in Performance Enhancement of Two‐Step Perovskite Photovoltaics

Much of the research efforts of late that are directed toward enhancement of the efficiency of perovskite‐based photovoltaics are focused on the application of ionic liquids (ILs) in a one‐step approach. On the contrary, the details of the alternative two‐step approach, such as the role of the ILs in the perovskite film solidification and its optoelectronic properties, remain poorly understood despite the increasing evidence that this latter method might offer considerable advantages, including better reproducibility and control over crystallization. Herein, the effect of IL methylammonium acetate (MAAc) introduced into the PbI2 layer by a sequential deposition process on the optoelectronic properties of the perovskite film and the performance of the ensuing photovoltaic devices are studied. The addition of MAAc lowers the MAAc–perovskite formation enthalpy, leading to an accelerated solidification process. Moreover, MAAc suppresses the formation of Pb0, thereby facilitating the perovskite formation while lowering the deep defect states caused by Pb0. In addition to grain boundary passivation, the acetate ions can diffuse into the bulk of the perovskite material, filling up the halide vacancies with reduced trap state density. As a result, a decent power conversion efficiency of 23.36% is achieved, with noticeably improved durability.

Immobilization of Conjugated Polymer Domains for Highly Stable Non-Fullerene-Based Organic Solar Cells.

To commercialize organic solar cells (OSCs), changes in the optimized morphology of the photoactive layer caused by external stimuli that cause degradation must be addressed. This work improves OSC stability by utilizing the cross-linking additive 1,8-dibromooctane (DBO) and a sequential deposition process (XSqD) to fabricate the photoactive layer. The cross-linking additive in the donor polymer (PTB7-Th) improves polymer crystallinity and immobilizes the crystalline morphology by partial photo-cross-linking. Ellipsometry experiments confirm the increase in the glass transition temperature of cross-linked PTB7-Th. The polymer crystallinity is further improved after removal of non-cross-linked polymer and residual additive by chlorobenzene. The cross-linked polymer layer forms an efficient and stable heterojunction with a nonfullerene acceptor (IEICO-4F) layer via an XSqD process. The OSC based on the immobilized PTB7-Th exhibits excellent stability against light soaking and thermal aging.

Layer-by-layer and non-halogenated solvent processing of benzodithiophene-free simple polymer donors for organic solar cells

High performance and easy-synthesis benzodithiophene (BDT)-free simple active layer materials, green non-halogen solvent processing and convenient device fabrication with batch-to-bath stability are all crucial to realize the industrial production of organic solar cells (OSCs) in the future. In this work, we develop two BDT-free polymer donors, PBTz-TC and PBTz-TTC, for green halogen-free solvent and layer-by-layer (LBL) processed high performance OSCs. The strong molecular aggregation of BTz units helps to improve the crystallinity and film-forming properties of the polymers, while the introduction of ester groups assists in enhancing the solubility of conjugated polymers in both halogen and non-halogen solvents and down-shifting the energy levels. The synergistic implementation of LBL method and orthogonal solvents can significantly reduce the scouring effect during the sequential deposition process, which is conducive to construct planar heterojunction. Due to the more planar conformation, PBTz-TTC possesses more robust film-forming property with superior corrosion resistance to the upper-layer than PBTz-TC. While, PBTz-TC better balances the independent film formation and moderate miscibility with IT-4F acceptor to favor stronger interaction at the donor/acceptor interfaces. Consequently, PBTz-TC shows much better performance than PBTz-TTC in both bulk heterojunction and LBL devices, ascribed to the better energy alignment, more favorable morphology and more efficient charge dynamic process. Notably, when treated with halogen-free solvent, an outstanding power conversion efficiency (PCE) of 12.81% with improved stability is achieved for PBTz-TC/IT-4F-based LBL device, which is the highest value of non-halogenated solvent processed devices based on benzodithiophene-free simple polymer donors. These findings provide a guideline for rational design of the environmental friendly simple polymer donor materials for further acceleration of the industrial production of OSCs.

A Modified Sequential Deposition Route for High-Performance Carbon-Based Perovskite Solar Cells under Atmosphere Condition.

Carbon-based hole transport material (HTM)-free perovskite solar cells have exhibited a promising commercialization prospect, attributed to their outstanding stability and low manufacturing cost. However, the serious charge recombination at the interface of the carbon counter electrode and titanium dioxide (TiO2) suppresses the improvement in the carbon-based perovskite solar cells’ performance. Here, we propose a modified sequential deposition process in air, which introduces a mixed solvent to improve the morphology of lead iodide (PbI2) film. Combined with ethanol treatment, the preferred crystallization orientation of the PbI2 film is generated. This new deposition strategy can prepare a thick and compact methylammonium lead halide (MAPbI3) film under high-humidity conditions, which acts as a natural active layer that separates the carbon counter electrode and TiO2. Meanwhile, the modified sequential deposition method provides a simple way to facilitate the conversion of the ultrathick PbI2 capping layer to MAPbI3, as the light absorption layer. By adjusting the thickness of the MAPbI3 capping layer, we achieved a power conversation efficiency (PCE) of 12.5% for the carbon-based perovskite solar cells.

Size-tunable MoS2nanosheets for controlling the crystal morphology and residual stress in sequentially deposited perovskite solar cells with over 22.5% efficiency

MoS2nano-scaffolds are introduced into the PbI2skeleton during a sequential deposition process to realize the homogeneous growth of perovskite crystals through expanding the physical volume of the PbI2layer and reducing film residual stress.

Binary sulfuric effect on ZnO laminated carbon nanofibers hybrid structure for ultrafast lithium storage capability

The hybrid structure of high conductive carbon materials with large capacitive metal compounds is one of promising strategies for achieving high specific capacity, cycling stability, and ultrafast Li-ion storage capability due to their synergistic effects. This article will demonstrate the novel hybrid structure of a zinc oxysulfide (ZnOS) lamination layer on a sulfur (S)-doped carbon nanofiber (SCNF) matrix via an electrospinning method with sequential atomic layer deposition (ALD) process and will also present the structural advantages for ultrafast Li-ion batteries (LIBs). As a double-anion material, ZnOS has benefits compared with single ZnO and ZnS during the charge/discharge process, which is accompanied with consecutive conversion and alloying reactions. To verify these factors, structural analysis at the atomic scale and various electrochemical properties were evaluated. The resultant ZnOS/SCNF electrode showed superior electrochemical performance such as high specific capacity (672.8 mAh g−1 at 100 mA g−1), good capacity retention (87.8% after 100 cycles), and excellent cycling stability (85.4% after 500 cycles). This is attributed to the facilitated kinetic properties including electron and ion transfer efficiency during the electrochemical reactions, accompanied with the ZnOS/SCNF hybrid structure. In this regards, we believe that the ZnOS/SCNF electrode could be a great reference as a promising research strategy for accomplishing ultrafast LIBs.

Optimization of solvent swelling for efficient organic solar cells via sequential deposition

Compared to bulk heterojunction (BHJ) organic solar cells (OSCs) prepared by the blend casting in “one step process”, sequential deposition (SD) processed OSCs can realize an ideal profile of vertical component distribution due to the swelling of polymer films. Herein, we did trials on several kinds of second solvents for swelling the polymer layer, and investigated the packing structure and morphology of the swollen films and the performance of the resulting devices. We found that an optimized morphology can be achieved by solvent swelling while using orthodichlorobenzene ( o -DCB) as the second layer processing-solvent, with polymer donor PffBT-3 as bottom layer, PC 71 BM as top layer and bicontinuous networks in the middle. Such solvent swelling process also makes the SD method exempt from thermal annealing treatment. The device based on SD yields a power conversion efficiency (PCE) up to 8.7% without any post-treatment, outperforming those from the devices based on SD using other solvents and that (7.06%) from BHJ device, respectively. We also extended the use of this approach to all-polymer blend system, and successfully improved the efficiency from 4.72% (chloroform) to 9.35% ( o -DCB), which is among the highest PCEs in all-polymer-based OSCs fabricated with SD method. The results demonstrate that the swelling of the polymer by the second layer solvent is a necessity for SD, paving the way towards additive-free high-performance OSCs. Solvent-swelling effect of the sequential deposition process is crucial for achieving desirable gradient separation along the vertical direction for efficient organic solar cells.

Alleviating halide perovskite surface defects

Alleviating halide perovskite surface defects

Double-layer CsI intercalation into an MAPbI3 framework for efficient and stable perovskite solar cells

The insufficient stability of CH 3 NH 3 PbI 3 (MAPbI 3 )-based perovskite solar cells (PSCs) remains a significant concern in this field of research, so a device engineering approach is required to obtain efficient, stable PSCs. The present work used a sequential deposition process to alternately fabricate thin MAPbI 3 -based perovskite and cesium iodide (CsI) layers with precise control over the CsI intercalation, producing high quality cesium containing perovskite films. The optimal CsI film thickness when applied to either the up, down or both layers of the MAPbI 3 perovskite film was also assessed. Interestingly, the application of a double layer CsI layer greatly altered the perovskite morphology to produce large grain sizes, as a result of the precise intercalation of the CsI molecules into the host MAPbI 3 . Furthermore, PSCs made with double layer CsI intercalation exhibited power conversion efficiencies as high as 18.43%. These exceeded the values obtained from devices made with pristine MAPbI 3 , or with CsI intercalation on either the bottom or top of the perovskite (16.14%, 17.92% and 17.26%, respectively). A double layer CsI intercalation device was stored in the dark at relative humidities of 40–50% for more than 4000 h and retained over 83% of its initial efficiency. Sequential deposition technique was used to alternately fabricate CH 3 NH 3 PbI 3 (MAPbI 3 ) and cesium iodide (CsI) thin layers with precise control over the CsI intercalation, producing large grain size, and high-quality cesium containing perovskite films. When the CsI double-layer intercalate into the MAPbI 3 framework effectively improves the efficiency and long-term stability of the perovskite solar cells. • Double layer CsI intercalation greatly altered the perovskite morphology. • The optimal CsI film thickness when applied to either the up, down or double layers of the MAPbI 3 film were assessed. • Double layer CsI intercalation significantly improve the long-term stability of perovskite solar cells.

All Slot‐Die Coated Non‐Fullerene Organic Solar Cells with PCE 11%

AbstractSlot‐die (SD) coating is used to fabricate fully solution processed organic solar cells (OSCs) based on a blend of high performance donor polymer (PTB7‐Th) and a non‐fullerene acceptor (IEICO‐4F) for stable devices over extended periods of operation. The optimization of a sequential deposition process of transport and active layers, under ambient conditions, enable high efficiency slot‐die coated solar cells with remarkable power conversion efficiencies (PCE) > 11.0% to bridge the gap between lab‐to‐fab. Fully slot‐die coated inverted OSCs are demonstrated with efficiencies reaching 11% along with 1 cm2 devices, proving the scalability and reproducibility of the proposed technique. Further, replacing the evaporated Ag electrode with solution processed Ag nanowire (AgNW) electrodes shows the highest light utilization efficiency of 5.26% for semi‐transparent OSC with a PCE of 9.07% and average visible transmission of 58%.