Chen Weijie

Publication date: December 2021

Source: Nano Energy, Volume 90, Part A

Author(s): Xiaoqing Jiang, Jiafeng Zhang, Yang Liu, Ziyuan Wang, Xuan Liu, Xin Guo, Can Li

The impact of different humidity conditions on the crystallization and degradation behaviors of BDAFA_n-1Pb_nI_3n+1 Dion–Jacobson perovskites is systematically investigated. An appropriate incorporation of water molecules greatly optimizes the optoelectronic properties and suppresses the phase dissociation. The BDAFA₅Pb₆I₁₉ perovskite solar cells with controlled incorporation of water molecules achieve an efficiency as high as 17.17% and demonstrate a high tolerance to the fabrication environment.

The Dion–Jacobson (DJ) perovskites solar cells (PSCs) demonstrate impressive humidity stability compared with 3D counterparts and have aroused extensive attention recently. However, it has not been investigated yet, how the humidity condition influences the photovoltaic performances. Herein, the effect of the humidity condition on the crystallization behavior, charge dynamics, photovoltaic and stability performances of BDAFA_n-1Pb_nI_3n+1 DJ perovskite is systematically investigated. Humidity-assisted annealing process can lead to reduced trap concentration and fast charge transfer process between different-n DJ phases. The BDAFA₅Pb₆I₁₉ PSC with the assistance of moisture achieves an efficiency as high as 17.17%, which is the highest value ever reported for methylammonium-free DJ PSCs. In addition, the humidity-, thermal-, and photo-stability properties of the DJ film and devices are significantly boosted. Further, first-principles calculation indicates that water molecules occupy the iodide vacancies through a strong bonding with Pb ions during the crystallization process under humidity and increase the decomposition energy of the DJ phase, which corresponds to the improved photoelectronic and stability properties. These results show that humidity-assisted deposition of 2D/3D multidimensional perovskite can be further explored to reduce the high demand of the production environment and enhance the performances.

Nature, Published online: 15 September 2021; doi:10.1038/d41586-021-02433-6

Room-temperature synthesized CsPbBr₃ nanocrystal (CN) is exploited as the bilateral interface modifier in perovskite layer for efficient planar perovskite solar cells (PSCs). Owing to the CN induced bilateral interfacial passivation and boosted built-in electric field, the charge separation and transfer are significantly ameliorated, which contribute to the superior power conversion efficiency exceeding 20% in CH₃NH₃PbI₃-based planar PSCs.

Abstract

Organic-inorganic halide perovskite solar cells (PSCs) have drawn tremendous attention owing to their remarkable photovoltaic performance and simple preparation process. However, conventional wet-chemical synthesis methods inevitably create defects both in the bulk and at the interfaces of perovskites, leading to recombination of charge carriers and reduced stability. Herein, a bilateral interface modification to perovskites by doping room-temperature synthesized CsPbBr₃ nanocrystals (CN) is reported. The ultrafast transient absorption measurement reveals that CN effectively suppresses the defect at the SnO₂/perovskite interface and boosts the interfacial electron transport. Meanwhile, the in situ Kelvin probe force microscopy and contact potential difference characterizations verify that the CN within the upper part of the perovskites enhances the built-in electric field, facilitating oriented migration of the carriers within the perovskite. Combining the superiorities of CN modifiers on both sides, the bilaterally modified CH₃NH₃PbI₃-based planar PSCs exhibit optimal power conversion efficiency exceeding 20% and improved device stability.

The reason for morphological differences in polymer:fullerene, polymer:nonfullerene small molecule, and polymer:polymer solar cells is revealed by studying their film formation through multiple in situ spectroscopies. The aggregation behavior of the higher molecular weight component, as well as the level of donor–acceptor interaction in the liquid film shows strong influence on the blend drying and its final morphology.

Abstract

The efficiency of bulk heterojunction (BHJ) based organic solar cells is highly dependent on the morphology of the blend film, which is a result of a fine interplay between donor, acceptor, and solvent during the film drying. In this work, a versatile set-up of in situ spectroscopies is used to follow the morphology evolution during blade coating of three iconic BHJ systems, including polymer:fullerene, polymer:nonfullerene small molecule, and polymer:polymer. the drying and photoluminescence quenching dynamics are systematically study during the film formation of both pristine and BHJ films, which indicate that the component with higher molecular weight dominates the blend film formation and the final morphology. Furthermore, Time-resolved photoluminescence, which is employed for the first time as an in situ method for such drying studies, allows to quantitatively determine the extent of dynamic and static quenching, as well as the relative change of quantum yield during film formation. This work contributes to a fundamental understanding of microstructure formation during the processing of different blend films. The presented setup is considered to be an important tool for the future development of blend inks for solution-cast organic or hybrid electronics.

This article demonstrates a novel synthetic strategy that can be used to tune the interstrand distance between conjugated polymers with unprecedented precision. This control provides an ideal platform for fundamental insight into the solid-state optical properties of NDI polymers.

Abstract

Conjugated polymers are an important class of chromophores for optoelectronic devices. Understanding and controlling their excited state properties, in particular, radiative and non-radiative recombination processes are among the greatest challenges that must be overcome. We report the synthesis and characterization of a molecularly encapsulated naphthalene diimide-based polymer, one of the most successfully used motifs, and explore its structural and optical properties. The molecular encapsulation enables a detailed understanding of the effect of interpolymer interactions. We reveal that the non-encapsulated analogue P(NDI-2OD-T) undergoes aggregation enhanced emission; an effect that is suppressed upon encapsulation due to an increasing π-interchain stacking distance. This suggests that decreasing π-stacking distances may be an attractive method to enhance the radiative properties of conjugated polymers in contrast to the current paradigm where it is viewed as a source of optical quenching.

Defect-triggered phase degradation has become the main issue in the field of inorganic CsPbI₃ perovskite. A crystal secondary growth of inorganic perovskites induced by a solid-state reaction to achieve defect compensation in CsPbI₃ perovskite is demonstrated. Finally, the defect-compensated CsPbI₃-based solar cell delivers 20.04% efficiency with excellent operational stability.

Abstract

Defect-triggered phase degradation is generally considered as the main issue that causes phase instability and limited device performance for CsPbI₃ inorganic perovskites. Here, a defect compensation in CsPbI₃ perovskite through crystal secondary growth of inorganic perovskites is demonstrated, and highly efficient inorganic photovoltaics are realized. This secondary growth is achieved by a solid-state reaction between a bromine salt and defective CsPbI₃ perovskite. Upon solid-state reaction, the Br⁻ ions can diffuse over the entire CsPbI₃ perovskite layer to heal the undercoordinated Pb²⁺ and conduct certain solid-state I/Br ion exchange reaction, while the organic cations can potentially heal the Cs⁺ cation vacancies through coupling with [PbI₆]⁴⁻ octahedra. The carrier dynamics confirm that this crystal secondary growth can realize defect compensation in CsPbI₃. The as-achieved defect-compensated CsPbI₃ not only improves the charge dynamics but also enhances the photoactive phase stability. Finally, the CsPbI₃-based solar cell delivers 20.04% efficiency with excellent operational stability. Overall, this work proposes a novel concept of defect compensation in inorganic perovskites through crystal secondary growth induced by solid-state reaction that is promising for various optoelectronic applications.

A green thermally activated delayed fluorescence (TADF) emitter with an extended π-system of linear donor (D)–acceptor (A)–donor (D) structure is established to simultaneously obtain a horizontal emitting dipole orientation ratio of 92%, a reverse intersystem crossing rate of 1.16 × 10⁶ s^–1 and a photoluminescence quantum yield of 95%, together affording a champion maximum external quantum efficiency of 39.1%.

Abstract

Thermally activated delayed fluorescence (TADF) emitters featuring preferential horizontal emitting dipole orientation (EDO) are in urgent demand for enhanced optical outcoupling efficiency in organic light-emitting diodes (OLEDs). However, simultaneously manipulating EDO and optoelectronic properties remains a formidable challenge. Here, an extended linear D–A–D structure with both enlarged donor (D) and acceptor (A) π-systems is established, not only elaborately manipulating parallel horizontal molecular orientation and EDO along its long axis by multi-driving-forces for a high horizontal dipole ratio (Θ _//), but also delocalizing distribution of frontier energy levels for optimized electronic properties. The proof-of-the-concept emitter simultaneously affords a high Θ _// of 92%, a high photoluminescence quantum yield of 95%, and a fast reverse intersystem crossing rate of 1.16 × 10⁶ s^-1. The corresponding OLED achieves a champion maximum external quantum efficiency of 39.1% among all green TADF devices without any external light-extraction techniques, together with a maximum power efficiency of 112.0 lm W^-1 and alleviated efficiency roll-off. These findings may inspire even better full-color TADF emitters that push the device efficiency toward the theoretical limits.

A novel process for atmospheric pressure dry etching of polysilicon layers is developed and integrated in industrial TOPCon solar cell process sequence. The process leads to very high etch rates (>3 μm min⁻¹) of parasitic polysilicon layer in a highly single-sided process. The fabricated large area TOPCon solar cells feature high parallel resistance and excellent reverse bias property.

Single-sided etching (SSE) of a-Si/poly-Si is typically considered a challenge for realizing a cost-efficient TOPCon production sequence, as there is a certain degree of unwanted wrap-around for poly-Si deposition technologies such as low pressure chemical vapor deposition, plasma-enhanced chemical vapor deposition, and atmospheric pressure chemical vapor deposition. To date, alkaline or acidic wet-chemical solutions in either inline or batch configurations are used for this purpose. Herein, an alternative SSE process is proposed using an inline dry etching tool, which applies molecular fluorine as the etching gas under atmospheric pressure conditions. The developed etching process performs complete etching of both as-deposited amorphous silicon and annealed polycrystalline silicon layers, either intrinsic or doped, and with measured etch rates of >3 μm min⁻¹ at 10% F₂ concentration allows etching of a typical layer thickness of 200 nm in just a few seconds. The etching process is also configured to perform excellent edge isolation while maintaining a low wrap-around etching (d _rear < 500 μm) at the opposing-side. The etching process is successfully transferred to the industrial TOPCon solar cell architecture, yielding high parallel resistances (S _shunt,avg. > 1500 kΩ cm²), low reverse current density (J _rev,avg < 0.8 mA cm⁻²) measured at a bias voltage of −12 V, and independently certified conversion efficiencies of up to 23.3%.

The effects of Cu (II) poly(styrene sulfonate) (Cu:PSS) on the electronic band structure and characteristics of organic solar cells are investigated. Easily reduced Cu²⁺ ions balance the negative charges on the PSS backbone, supporting p-doping at the interface with PTB7. Photoelectron spectroscopy confirms a band-bending effect, consistent with the observed hole extracting effects of Cu:PSS in solar cells.

In organic solar cells (OSCs), interfacial properties between the donor phase and hole transport layers (HTLs) are critical factors which govern charge extraction efficiency. Many ionic and polar materials are known to function as effective interfacial layers; however, an understanding of how ionic moieties affect the electronic band structure and characteristics of OSCs is lacking. Herein, a new, pH-neutral polyelectrolyte is introduced that resolves several problems which are encountered with the commonly used HTL, poly(3,4-ethylenedioxythiopene):polystyrenesulfonate (PEDOT:PSS). An effective p-type polyelectrolyte dopant is designed, comprising an anionically charged PSS backbone with easily reduced Cu²⁺ counterions (Cu:PSS), and interfacial properties for HTL/donor interfaces by photoelectron spectroscopy are analyzed. The effects of the polyelectrolyte on interfacial energy levels and charge extraction efficiency between the active layer and HTL are quantified. Using optimized processing conditions, the efficiency can be improved from 8.31% to 9.28% in conventional OSCs compared with a standard PEDOT:PSS HTL. The energy-level alignment at the HTLs/donor interface determined by UV photoelectron spectroscopy measurements reveals the origin of distinct differences in device performances. The reduced ionization potential (IP) and hole injections barrier (Φ_h) at the HTL/donor interface play a crucial role in efficient charge extraction in conventional OSCs.

Phosphorus-doped poly-SiN _x as a new material, featuring significant nitrogen doping and low crystalline degree, is introduced to passivating contact, leading to excellent passivation quality with a champion iV _oc of 745 mV and enabling the efficiency of the proof-of-concept tunnel oxide passivated contact solar cell to 23.88%.

A P-doped polycrystalline silicon-nitride (n-poly-SiN _x ) as the electron selective collection layer in a tunnel oxide passivated contact (TOPCon) solar cell is reported. The nitrogen content is controlled by the active gas ratio of R = NH₃/(SiH₄ + NH₃) during the plasma-enhanced chemical vapor deposition (PECVD) process. The effects of R ratio on the material's composition, crystallinity, surface passivation, and contact resistivity are investigated. The poly-SiN _x contact exhibits improved surface passivation in comparison with the reference poly-Si without N incorporation. The best double-sided passivated n-type alkaline-polished crystalline silicon wafer with the n-poly-SiN _x /SiO _x manifests the highest implied open-circuit voltage (iV _oc) of ≈745 mV, with the corresponding single-sided saturated current density of 1.7 fA cm⁻² and the effective lifetime (τ _eff) of 10 ms at the injection level of ≈1 × 10¹⁵cm⁻³. In contrast, the controlled sample with an n-poly-Si/SiO _x passivation contact has a maximal iV _oc of 738 mV. However, the primary drawback of the N doping is to raise the contact resistivity, but which is still in an acceptable range and shows little effect on the performance of solar cell with full-area contact. The proof-of-concept TOPCon solar cell using the n-poly-SiN _x /SiO _x passivating contact has achieved an efficiency of 23.88%, indicating the potential of the n-poly-SiN _x for high-efficiency TOPCon solar cells.

Publication date: December 2021

Source: Nano Energy, Volume 90, Part A

Author(s): Ling Liu, Chuantian Zuo, Liming Ding

A hybrid amyloid-like protein nanofilm with high mechanical strength and robust interfacial adhesion shows high interfacial activity to induce electroless deposition of metal on a flexible substrate, and significantly diminishes the development of microcracks after repetitive bending or stretching of metal-coated polymer substrates. This work demonstrates the significant contribution of amyloid-like protein aggregation in the fabrication of flexible conductive devices.

Abstract

A fatal weakness in flexible electronics is the mechanical fracture that occurs during repetitive fatigue deformation; thus, controlling the crack development of the conductive layer is of prime importance and has remained a great challenge until now. Herein, this issue is tackled by utilizing an amyloid/polysaccharide molecular composite as an interfacial binder. Sodium alginate (SA) can take part in amyloid-like aggregation of the lysozyme, leading to the facile synthesis of a 2D protein/saccharide hybrid nanofilm over an ultralarge area (e.g., >400 cm²). The introduction of SA into amyloid-like aggregates significantly enhances the mechanical strength of the hybrid nanofilm, which, with the help of amyloid-mediated interfacial adhesion, effectively diminishes the microcracks in the hybrid nanofilm coating after repetitive bending or stretching. The microcrack-free hybrid nanofilm then shows high interfacial activity to induce electroless deposition of metal in a Kelvin model on a substrate, which noticeably suppresses the formation of microcracks and consequent conductivity loss during the bending and stretching of the metal-coated flexible substrates. This work underlines the significance of amyloid/polysaccharide nanocomposites in the design of interfacial binders for reliable flexible electronic devices and represents an important contribution to mimicking amyloid and polysaccharide-based adhesive cements created by organisms.

[C(NH₂)₃]ClO₄-polyurethane flexible sensors feature a series of unique characteristic including self-powering, high sensitivity, and excellent durability. A comprehensive scaling analysis along with computational modeling provides insights into the electro-mechanical coupling and establishes the rules of engineering design and optimization for the molecular ferroelectric-based flexible sensors.

Abstract

Although excellent dielectric, piezoelectric, and pyroelectric properties matched with or even surpassing those of ferroelectric ceramics have been recently discovered in molecular ferroelectrics, their successful applications in devices are scarce. The fracture proneness of molecular ferroelectrics under mechanical loading precludes their applications as flexible sensors in bulk crystalline form. Here, self-powered flexible mechanical sensors prepared from the facile deposition of molecular ferroelectric [C(NH₂)₃]ClO₄ onto a porous polyurethane (PU) matrix are reported. [C(NH₂)₃]ClO₄-PU is capable of detecting pressure of 3 Pa and strain of 1% that are hardly accessible by the state-of-the-art piezoelectric, triboelectric, and piezoresistive sensors, and presents the ability of sensing multimodal mechanical forces including compression, stretching, bending, shearing, and twisting with high cyclic stability. This scaling analysis corroborated with computational modeling provides detailed insights into the electro-mechanical coupling and establishes rules of engineering design and optimization for the hybrid sponges. Demonstrative applications of the [C(NH₂)₃]ClO₄-PU array suggest potential uses in interactive electronics and robotic systems.

A solar cell device based on (hk1)-oriented Sb₂(S,Se)S₃ grown on top of hexagonal CdS is successfully prepared. The enhanced device performance is attributed not only to the faster charge transport along the vertically oriented (Sb₄X₆) _n ribbons, but also to the efficient charge extraction across the heterojunction owing to the formation of favorable covalent bond at the junction.

Abstract

Antimony sulfoselenide (Sb₂(S,Se)₃) is a promising photoabsorber for stable and high efficiency thin film photovoltaics (PV). The unique quasi-1D (Q1D) crystal structure gives Sb₂(S,Se)₃ intriguing anisotropic optoelectronic properties, which intrinsically require the optimization of crystal growth orientation, especially for electronic devices with vertical charge transport such as solar cells. Although the efficiency of Sb₂(S,Se)₃ solar cells has been improved greatly through optimizing the material quality, the fundamental issue of crystal orientation control in polycrystalline films remains unsolved, resulting in charge carrier recombination losses in the device. Herein, the epitaxial growth of vertically-oriented Sb₂(S,Se)₃ film on hexagonal CdS is successfully realized via a solution-based synergistic crystal growth process. The crystallographic orientation relationship between Sb₂(S,Se)₃ light absorber and the CdS substrate has been rigorously investigated. The best performing Sb₂(S,Se)₃ solar cell shows a high power conversion efficiency of 9.2% owing to the faster charge transport in the bulk and the efficient charge extraction across the heterojunction. This study points to a new direction to control the crystal growth of mixed-anion Sb₂(S,Se)₃, which is crucial to achieve high efficiency solar cells based on antimony chalcogenides with low dimensionality.

A hybrid planar/bulk heterojunction is constructed by introducing a p-type polymer (PTO3) and an n-type naphthalene imide (NDI-i8) on both sides of a mixed donor:acceptor active layer. The tailored hybrid heterojunction presents a decreased energy loss and improved efficiency. As a result, an outstanding PCE of 18.5% is achieved, which is among the top values in the field of organic solar cells.

Abstract

The donor:acceptor heterojunction has proved as the most successful approach to split strongly bound excitons in organic solar cells (OSCs). Establishing an ideal architecture with selective carrier transport and suppressed recombination is of great importance to improve the photovoltaic efficiency while remains a challenge. Herein, via tailoring a hybrid planar/bulk structure, highly efficient OSCs with reduced energy losses (E _losss) are fabricated. A p-type benzodithiophene-thiophene alternating polymer and an n-type naphthalene imide are inserted on both sides of a mixed donor:acceptor active layer to construct the hybrid heterojunction, respectively. The tailored structure with the donor near the anode and the acceptor near the cathode is beneficial for obtaining enhanced charge transport, extraction, and suppressed charge recombination. As a result, the photovoltaic characterizations suggest a reduced nonradiative E _loss by 25 meV, and the best OSC records a high efficiency of 18.5% (certified as 18.2%). This study highlights that precisely regulating the structure of donor:acceptor heterojunction has the potential to further improve the efficiencies of OSCs.