Chen Weijie

Amphiphilic supramolecular adhesives with low glass transition temperature and massive hydrogen bonds were designed by random copolymerization of acrylamide and n-butyl acrylate. The adhesive dopant facilitates a dynamic thermal self-healing effect at only 70 °C and contributes to efficient and highly flexible perovskite solar cells.

Abstract

Flexible perovskite solar cells (FPSCs) have attracted great attention due to their advantageous traits such as low cost, portability, light-weight, etc. However, mechanical stability is still the weak point in their practical application. Herein, we prepared efficient FPSCs with remarkable mechanical stability by a dynamic thermal self-healing effect, which can be realized by the usage of a supramolecular adhesive. The supramolecular adhesive, which was obtained by random copolymerization of acrylamide and n-butyl acrylate, is amphiphilic, has a proper glass transition temperature and a high density of hydrogen-bond donors and receptors, providing the possibility of thermal dynamic repair of mechanical damage in FPSCs. The adhesive also greatly improves the leveling property of the precursor solution on the hydrophobic poly[bis(4-phenyl)(2,4,6-trimethylphenyl)]amine (PTAA) surface. PSCs containing this adhesive achieve more than a 20 % power conversion efficiency (PCE) on flexible substrates and a 21.99 % PCE on rigid substrates (certified PCE of 21.27 %), with improved electron mobility and reduced defect concentration.

Publication date: March 2022

Source: Nano Energy, Volume 93

Author(s): Dae Hwan Lee, Do Hui Kim, Taehyun Kim, Dong Chan Lee, Shinuk Cho, Taiho Park

A water-soluble, self-healing, and polysulfide-trapping binder named polyvinylpyrrolidone-polyethyleneimine is reported and used in flexible lithium-sulfur batteries to improve their electrochemical performance.

Abstract

Wearable electronics require lightweight and flexible batteries, of which lithium-sulfur (Li-S) batteries are of great interest due to their high gravimetric energy density. Nevertheless, flexible Li-S batteries have unsatisfactory electrochemical performance owing to electrode fracture during repeated bending, the volume change of sulfur species and the severe shuttle effect. Binders play essential roles in these batteries but have always lacked attention. Herein, a self-healing polyvinylpyrrolidone-polyethyleneimine (PVP-PEI) binder cross-linked by hydrogen bonds, which also regulates polysulfide redox kinetics, is reported. The dynamic hydrogen-bonding networks repair the cracks and ensure the integrity of the electrode while numerous polar groups such as CO and -NH₂ suppress the shuttle effect by immobilizing polysulfides. Therefore, Li-S batteries with the PVP-PEI binder exhibit excellent cycling stability (a capacity decay rate of 0.0718% per cycle at 1 C after 450 cycles), an outstanding areal capacity of 7.67 mAh cm⁻² even under a high sulfur loading (7.1 mg cm⁻²) and relatively lean electrolyte conditions (E/S ratio = 8 µL mg⁻¹). Flexible Li-S pouch cells using the PVP-PEI binder show a stable performance for 140 cycles and a favorable capacity retention of over 95% after 2800 bending cycles, confirming its application potential in high-performance flexible Li-S batteries.

An ionic liquid (IL) is designed to passivate undercoordinated Pb²⁺ by chemically bonding to form an IL capped perovskite surface, leading to superior photovoltaic performance and operational stability. Specifically, the small solar cell (0.1 cm²) exhibits an open-circuit voltage of 1.192 V, power conversion efficiency of 24.33%, and the large area (10.75 cm²) integrated module achieves a PCE of 20.33%.

Abstract

Metal-halide perovskite has emerged as an effective photovoltaic material for its high power conversion efficiency (PCE), low cost and straightforward fabrication techniques. Unfortunately, its long-term operational durability, mainly affected by halide ion migration and undercoordinated Pb²⁺ is still the bottleneck for its large-scale commercialization. In this work, an ionic liquid (IL) is designed to effectively cap the grain surface for improved stability and reduced trap density. More specifically, the Br⁻ in the IL passivates the undercoordinated Pb²⁺ by chemically bonding to it, resulting in a thin layer of ionic-liquid-perovskite formed on the surface, leading to improved photovoltaic performance and better stability. Specifically, the solar cell exhibits an open-circuit voltage of 1.192 V and PCE of 24.33% under one-sun illumination with negligible hysteresis, and a large area (10.75 cm²) integrated module achieves PCE of 20.33%. Moreover, the bare device maintains over 90% of its initial efficiency after 700 h of aging at 65 °C. It also shows outstanding stability with only about 10% degradation after being exposed to the ambient environment for 1000 h. The superior efficiency and stability demonstrate that the present IL passivating strategy is a promising approach for high-performance large area perovskite solar cell applications.

Perovskite solar cells (PSCs) have demonstrated enormous potential as next generation of photovoltaic technologies. Herein, the latest advances of interfacial materials for highly efficient and stable PSCs are summarized with organized classification. The theory and multifaceted roles of interface engineering are analyzed and insights on the deposition strategy of interlayers and outlook of interface engineering for PSCs toward commercialization are provided.

Abstract

Organic–inorganic lead halide perovskite solar cells (PSCs) have demonstrated enormous potential as a new generation of solar-based renewable energy. Although their power conversion efficiency (PCE) has been boosted to a spectacular record value, the long-term stability of efficient PSCs is still the dominating concern that hinders their commercialization. Notably, interface engineering has been identified as a valid strategy with extraordinary achievements for enhancing both efficiency and stability of PSCs. Herein, the latest research advances of interface engineering for various interfaces are summarized, and the basic theory and multifaceted roles of interface engineering for optimizing device properties are analyzed. As a highlight, the authors provide their insights on the deposition strategy of interlayers, application of first-principle calculation, and challenges and solutions of interface engineering for PSCs with high efficiency and stability toward future commercialization.

Publication date: March 2022

Source: Nano Energy, Volume 93

Author(s): Insik Yun, Yeonghee Lee, Young-Geun Park, Hunkyu Seo, Won Gi Chung, Soo-Jin Park, Jin-Woo Cho, Jun Hyeok Lee, Ravi Prakash Srivastava, Rira Kang, Byunghong Lee, Dahl-Young Khang, Sun-Kyung Kim, Jun Hong Noh, Jang-Ung Park

The synergistic optimization of 4-aminomethyltetrahydropyran and 1-chlorobutane successfully passivates cation and anion defects, effectively mitigates carrier nonradiative recombination, and achieves perovskite solar cells with high photovoltaic performance and a champion power conversion efficiency of 22.74%.

Perovskite layer, as the origin of optical–electrical conversion of devices, plays a very important role in perovskite solar cells (PSCs). However, lots of lead cations and halogen anions defects inevitably exit in the bulk and surface of the perovskite layer. These defects, serve as nonradiative recombination centers, degrade the performance, and damage the stability of PSCs. Herein, a strategy that anion and cation defects on the interface and in the bulk of perovskites are simultaneously passivated by doping organic molecule 4-aminomethyl tetrahydropyran (4-AMPR) and the surface modification with 1-chlorobutane (1-CB) in/on the perovskite is demonstrated. The O atoms on 4-AMPR can coordinate with the Pb vacancy and antisite Pb defects, as well as improve perovskite morphology. The volatilization of low-boiling 1-CB can passivate the halogen ion defects and promote the uniform nucleation of perovskite. The PSCs jointly optimized by 4-AMPR and 1-CB achieve a power conversion efficiency of 22.74% and retain 90.7% of the initial efficiency after storage in air environment (RH 10 ± 5%, 25 °C) for more than 1000 h. This research demonstrates a promising strategy for simultaneously mitigating anion and cation defects both in bulk and surface of perovskite layer and thus enhancing the performance and stability of the devices.

An amphoteric phenylbenzimidazole sulfonic acid is used to simultaneously regulate crystallization growth, passivate defects, and mitigate lead leakage of high-performance perovskite solar cells. The efficiency of the optimized device is 23.27% (0.09 cm²) and 15.31% (19.32 cm²), respectively. Meanwhile, the leakage of lead ions from unencapsulated devices is also successfully suppressed.

Abstract

With the continuous improvement of performance of lead-based perovskite solar cells (PSCs), the potential harm of water-soluble lead ion (Pb²⁺) to environment and public health is emerging as a major obstacle to their commercialization. Herein, an amphoteric phenylbenzimidazole sulfonic acid (PBSA) that is almost insoluble in water is added to the perovskite precursor to simultaneously regulate crystallization growth, passivate defects, and mitigate lead leakage of high-performance PSCs. Through systematic research, it is found that PBSA can not only regulate the crystallization of perovskite grains to form the film, but also passivate the defects of annealed films mainly due to the strong interaction between the functional groups in PBSA and Pb²⁺, which greatly improves the crystallinity and stability of perovskite films. Consequently, the highest power conversion efficiency of 23.27% is achieved in 0.09 cm² devices and 15.31% is obtained for large-area modules with an aperture area of 19.32 cm², along with negligible hysteresis and improved stability. Moreover, the leakage of lead ions from unpackaged devices is effectively prevented owing to the strong coupling between PBSA molecules and water-soluble Pb²⁺ to form insoluble complexes in water, which is of great significance to promote the application of optoelectronic devices based on lead-based perovskite materials.

High-efficiency air-fabricated inverted CsPbI₃ PSCs with a wide humidity operating window are realized via an in situ stabilizing strategy. During operation in humidity air, maleic anhydride (MAAD) molecules can convert harmful water erosions into a stabilizer to regulate crystallization and suppress phase transition of CsPbI₃ film. The inverted devices realize champion efficiency of 19.25% with good stability and wide humidity operating window.

Abstract

Inverted triiodine cesium lead (CsPbI₃) perovskite solar cells (PSCs) are promising in photovoltaics owing to their ideal light absorption, non-volatile active layer, and avoidance of fragile Spiro-OmeTAD, especially as the top cell in tandem devices. However, they still exhibit far-lagging efficiency, and must be processed in a strictly controlled environment due to water-fearing CsPbI₃. Here, a novel strategy to convert the harmful water erosions into an in situ stabilizer for efficient inverted CsPbI₃ PSCs fabricated with a wide humidity operating window, is proposed. During air fabrication, maleic anhydride (MAAD) can react with water molecules in air to reduce moisture erosions, while the hydrolysis products (maleic acid, MAAC) control grains growth. After annealing, MAAC strongly binds to CsPbI₃ grains as a shield to hamper phase transition and moisture penetration. A champion efficiency of 19.25% is obtained, which is the highest efficiency among the inverted inorganic PSCs. In parallel, the authors’ optimized devices present efficiency of 18.39% even fabricated in relative humidity 60% condition. Moreover, the stability against various ages is improved, and the optimized devices remain at 96.8% of its initial efficiency after maximum power point tracking at 65 °C for 850 h.

Single-crystal solar cells with high efficiency and a superior weak light response are achieved by engineering the hole extraction interface. Remarkably enhanced efficiency of 22.1% under AM 1.5G irradiation and indoor efficiency of 39.2% under 1000 lux irradiation are obtained, which are both the highest values for MAPbI₃ single-crystal solar cells.

Abstract

Perovskite single crystals have recently been regarded as emerging candidates for photovoltaic application due to their improved optoelectronic properties and stability compared to their polycrystalline counterparts. However, high interface and bulk trap density in micrometer-thick thin single crystals strengthen unfavorable nonradiative recombination, leading to large open-circuit voltage (V _OC) and energy loss. Herein, hydrophobic poly(3-hexylthiophene) (P3HT) molecule is incorporated into a hole transport layer to interact with undercoordinated Pb²⁺ and promote ion diffusion in a confined space, resulting in higher-quality thin single crystals with reduced interface and bulk defect density, suppressed nonradiative recombination, accelerated charge transport, and extraction. As a result, a remarkably enhanced V _OC of up to 1.13 V and efficiency of 22.1% are achieved, which are both the highest values for MAPbI₃ single-crystal solar cells. Moreover, the reduced defect density and suppressed carrier recombination lead to superior weak light response of the single-crystal solar cells after incorporation of P3HT, and an indoor photovoltaic efficiency of 39.2% at 1000 lux irradiation is obtained.

Direct phase transformation grain growth mechanism is demonstrated from a solution-processed chalcopyrite structured precursor film, which enables fabrication of a highly efficient CuIn(S,Se)₂ (CISSe) solar cell near stoichiometric composition without the detrimental Cu_{2− x} Se due to its high tolerance to the Cu/In ratio (from 0.90 to 1.05). By preliminary optimization, a 13.6% efficient CISSe device is fabricated from an N-methyl-pyrrolidone solution processed in ambient air.

Abstract

Solution-processed Cu(In,Ga)(S,Se)₂ solar cells have reached 18% efficiency but still remain much lower compared to state-of-the-art vacuum based solar cells. In comparison to vacuum deposited precursor films, which mostly consist of stacked metal and/or metal chalcogenide layers and takes a liquid Cu_{2− x} Se assisted grain growth mechanism, solution-processed precursor films normally have a chalcopyrite structure that is already developed. Understanding the grain growth mechanism of solution-processed absorbers is crucial to control the electronic properties and further improve the device photovoltaic performance. Here, the grain growth mechanism of a N-methyl-pyrrolidone solution processed precursor film with composition from Cu-poor to Cu-rich is systematically investigated. Characterizations show that the chalcopyrite structured CuInS₂ precursor film takes a direct phase transformation grain growth mechanism and forms the CuIn(S,Se)₂ (CISSe) absorber without the presence of a detrimental Cu_{2− x} Se phase with Cu/In ratio up to unit. Beyond the stoichiometric composition, the coexistence of Cu_{2− x} Se facilitates grain growth but deteriorates device performance. The direct phase transformation mechanism not only avoids detrimental Cu_{2− x} Se but also enables fabrication of a highly efficient CISSe device near stoichiometric composition with high tolerance to the Cu/In ratio (from 0.90 to 1.05). By preliminary optimization, a CISSe solar cell with an efficiency of 13.6% is achieved in ambient air with a Cu/In ratio of 0.93.

An N-substituted asymmetric nonfullerene acceptor SN with an over 40 nm bathochromically shifted absorption compared to Y6 is designed and synthesized. The PM6 : SN-based binary cell exhibits the lowest nonradiative voltage loss of 0.15 eV ever achieved by organic solar cells (OSCs). Benefiting from extended NIR absorption and lowered voltage loss, PM6 : Y6 : SN-based semitransparent (ST)-OSCs, for the first time, achieve a power conversion efficiency of 14 % with an average visible transmittance over 20 %.

Abstract

Semitransparent organic solar cells (ST-OSCs) are considered as one of the most valuable applications of OSCs and a strong contender in the market. However, the optical band gap of current high-performance ST-OSCs is still not low enough to achieve the optimal balance between power conversion efficiency (PCE) and average visible transmittance (AVT). An N-substituted asymmetric nonfullerene acceptor SN with over 40 nm bathochromically shifted absorption compared to Y6 was designed and synthesized, based on which the device with PM6 as donor obtained a PCE of 14.3 %, accompanied with a nonradiative voltage loss as low as 0.15 eV. Meanwhile, ternary devices with the addition of SN into PM6 : Y6 can achieve a PCE of 17.5 % with an unchanged open-circuit voltage and improved short-circuit current. Benefiting from extended NIR absorption and lowered voltage loss, ST-OSCs based on PM6 : SN : Y6 were fabricated and the optimized device demonstrated a PCE of 14.0 % at an AVT of 20.2 %, which is the highest PCE at an AVT over 20 %.

Publication date: March 2022

Source: Nano Energy, Volume 93

Author(s): Yue Zhang, Baoqi Wu, Yakun He, Wanyuan Deng, Jingwen Li, Junyu Li, Nan Qiao, Yifan Xing, Xiyue Yuan, Ning Li, Christoph J. Brabec, Hongbin Wu, Guanghao Lu, Chunhui Duan, Fei Huang, Yong Cao

A self-healing effect of voids in double-perovskites is reported. Nanocrystals placed under electron beam irradiation will develop crystal voids which will migrate through the crystal. Surface ligand passivation of the nanocrystal confines the voids to inner crystal parts. The removal of the ligands enables annealing of the voids and self-healing of the crystal.

Abstract

Double perovskites are considered for future photovoltaic and electro-optic applications as a toxic-free alternative to lead halide perovskites. Alas, due to the lower efficiency of lead-free devices, material properties need to improve to compete. In this work, the self-healing and annealing of crystal voids is reported. Experiments are conducted on nanocrystals and in situ a transmission electron microscopy (TEM) microscope. The setup enables creation of crystal voids and to monitor their dynamics in real time. Void trajectories and velocities are calculated for TEM videos. An inaccessible, protected volume for migration near the nanocrystal outer surface is discovered, confining the migration of voids to inner crystal parts. Once surface passivation in the form of organic ligands is removed, void dynamics changes, to enable annealing of the voids and self-healing of the crystal. It is determined that surface ligand protection against void migration is extending several atomic layers below the crystal surface. Modeling based on these results predict equilibrium positions for the voids, which are discovered in the data. The study suggests that tuning of organic ligand density influences structural stability and crystal defect tolerance in double perovskites. Engineering surfaces with inherent self-healing properties may increase efficiencies in future devices based on these materials.