Chen Weijie

The discussion focuses on how the crystallographic properties and the structure of the Ruddlesen–Popper perovskite impact the efficiency of the solar cells. The strategies for film processing and material design in past studies and the potential research directions in the future are discussed.

Abstract

Metal halide Ruddlesen–Popper perovskite solar cells (RPPSCs) have attracted a great deal of attention in the research community due to their excellent stability over the 3D counterparts. In 2014, the first RPPSC was reported achieving a power conversion efficiency (PCE) of about 4.7%. To date, this type of solar cells reach a PCE exceeding 18% on lab scale. In this essay, distil strategies to further improve the PCE of RPPSCs are discussed. First, the unique physical properties of RPP are discussed to highlight the importance of film processing and material design, and then the factors that are limiting RPPSCs with special focus on the crystallographic and charge transport properties are addressed. Finally, the opportunities for RPPSCs are discussed, and opinions are provided regarding how to further improve the performance of these devices and on strategies which may advance the technology toward its industrial exploitation.

Semiconducting oxide overlayer materials (SOOMs) can offer a new way for low-cost and highly-stable halide perovskite solar cells (HPSCs) compared to organic semiconducting overlayer materials. The effective deposition of SOOMs on top of the perovskite layer is expected to contribute to the commercialization of single-junction as well as multi-junction HPSCs.

Abstract

Halide perovskite solar cells (HPSCs) contain charge transport layers (CTLs) both above and below the photoactive perovskite layer. These semiconducting CTLs are just as important as the perovskite layer to fully realizing the potential of perovskite materials. In particular, semiconducting oxide overlayer materials (SOOMs) are expected to lower costs and provide better long-term stability compared to the organic semiconducting materials commonly used for the upper layer. However, SOOM-based HPSCs are currently less efficient than conventional devices owing to SOOM's deposition constraints imposed by the underlying perovskite layer. This progress report focuses on the recent evolution of SOOM-based HPSCs by describing the key issues and recent advances in SOOM deposition methods. Finally, remaining challenges and future research directions for SOOMs are discussed to provide guidance toward the commercialization of HPSCs.

Three structurally similar non‐fullerene acceptors with various outer side chains are designed and matched with a cost‐effective donor polymer named PTQ10 to fabricate organic solar cells. High efficiencies of 17.1% and 17.6% are achieved by the PTQ10‐based binary and ternary devices, respectively, demonstrating the significance of material compatibility in fine‐tuning morphology toward high‐performance organic photovoltaics.

Abstract

In this work, the properties and performance of three structurally similar non‐fullerene acceptors (named BTP‐Ph, BTP‐Th, and BTP‐C11) possessing different side chains on the β‐positions of the thienothiophene units of the Y6 molecule are systematically studied. The steric and electronic effects of these side chains on the blend morphology and device performance based on the PTQ10 donor polymer are investigated. It is found that the thiophene and benzene units on the side chains introduce more steric hindrance and thus slightly reduce the crystallinity of the molecule. However, an interesting matching trend with the PTQ10 donor that appears to better match with the less crystalline molecules is observed. Overall, PTQ10:BTP‐Ph delivers the highest performance of 17.1% due to the suitable phase separation among three blends. Next, a ternary strategy is explored by incorporating BTP‐Th/BTP‐C11 with better molecular packing into PTQ10:BTP‐Ph, which successfully extends photon response, enhances charge transport, and suppresses charge recombination compared with the binary blend. Due to these synergistic effects, the ternary device based on PTQ10:BTP‐Ph:BTP‐Th achieves an outstanding power conversion efficiency of 17.6% with a fill factor of 78.8%, which is the highest value of PTQ10‐based devices to date.

A novel naphtho[2,3‐b:6,7‐b′]difuran (NDF)‐based copolymer NDF‐3T is designed and applied in organic solar cells (OSCs). The champion device based on NDF‐3T/ ITIC‐4Cl shows a PCE of 14.21%, due to the favorable molecular conformational modulation. Importantly, 14.21% is the highest PCE reported for furan‐based single‐junction OSCs. Therefore, the NDF is shown to be a promising building block in organic electronic materials.

Abstract

As one kind of abundant product from renewable resources, furan and its fused‐ring derivatives, have provoked great interest in the context of developing efficient photovoltaic materials. However, the power conversion efficiency (PCE) of furan‐based photovoltaic materials has lagged behind its thiophene counterparts. In this work, in consideration of the ordered π–π stacking via extending conjugation to further improve the charge mobility, a novel furan fused‐ring derivative of naphtho[2,3‐b:6,7‐b′]difuran (NDF) based copolymer of NDF‐3T is designed and synthesized. Because of its favorable linear molecular conformation, the NDF‐3T possesses a high crystallinity, as well as ordered and dense π–π stacking. Subsequently, the NDF‐3T‐based device exhibits an efficient PCE of 14.21%, which is higher than that of the analogue naphthodithiophene (NDT) counterpart (10.86%). To the best of the authors’ knowledge, the PCE is also the best record in furan‐based photovoltaic materials. More importantly, the development of line NDF shows great potential in construing highly efficient photovoltaic materials and can be referenced to other furan fused‐ring structures.

Nature Communications, Published online: 01 March 2021; doi:10.1038/s41467-021-21676-5

Nature Photonics, Published online: 01 March 2021; doi:10.1038/s41566-021-00766-2

The organic component in 2D layered perovskites can grant access to many possibilities for material design, in view of the rich variety. This work shows how the choice of the structure and chain length of organic cations can effectively guide the precise design of the emission color and efficiency of such versatile nanomaterials.

Abstract

The unique combination of organic and inorganic layers in 2D layered perovskites offers promise for the design of a variety of materials for mechatronics, flexoelectrics, energy conversion, and lighting. However, the potential tailoring of their properties through the organic building blocks is not yet well understood. Here, different classes of organoammonium molecules are exploited to engineer the optical emission and robustness of a new set of Ruddlesden–Popper metal‐halide layered perovskites. It is shown that the type of molecule regulates the number of hydrogen bonds that it forms with the edge‐sharing [PbBr₆]^4‐ octahedra layers, leading to strong differences in the material emission and tunability of the color coordinates, from deep‐blue to pure‐white. Also, the emission intensity strongly depends on the length of the molecules, thereby providing an additional parameter to optimize their emission efficiency. The combined experimental and computational study provides a detailed understanding of the impact of lattice distortions, compositional defects, and the anisotropic crystal structure on the emission of such layered materials. It is foreseen that this rational design can be extended to other types of organic linkers, providing a yet unexplored path to tailor the optical and mechanical properties of these materials and to unlock new functionalities.

Nature Communications, Published online: 26 February 2021; doi:10.1038/s41467-021-21493-w

Publication date: 17 March 2021

Source: Joule, Volume 5, Issue 3

Author(s): Chaoyang Kuang, Zhangjun Hu, Zhongcheng Yuan, Kaichuan Wen, Jian Qing, Libor Kobera, Sabina Abbrent, Jiri Brus, Chunyang Yin, Heyong Wang, Weidong Xu, Jianpu Wang, Sai Bai, Feng Gao

Publication date: Available online 19 February 2021

Source: Joule

Author(s): Kaitlyn T. VanSant, Adele C. Tamboli, Emily L. Warren

Publication date: 8 April 2021

Source: Chem, Volume 7, Issue 4

Author(s): Samik Jhulki, Hio-Ieng Un, Yi-Fan Ding, Chad Risko, Swagat K. Mohapatra, Jian Pei, Stephen Barlow, Seth R. Marder

Publication date: 13 May 2021

Source: Chem, Volume 7, Issue 5

Author(s): Jiaqiang Li, Zhicheng Zhang, Ya Kong, Binwei Yao, Chen Yin, Lianming Tong, Xudong Chen, Tongbu Lu, Jin Zhang

Nature Materials, Published online: 25 February 2021; doi:10.1038/s41563-021-00944-1

Nature Photonics, Published online: 15 February 2021; doi:10.1038/s41566-021-00763-5

Nature Photonics, Published online: 24 February 2021; doi:10.1038/s41566-021-00772-4

Recent years have witnessed substantial progress in nanostructured‐perovskite‐based devices. Patterning and integration techniques for nanostructured perovskites are summarized and recent progress in novel nanostructured‐perovskite‐based applications is presented.

Abstract

In the past decade, lead halide perovskites have been intensively explored due to their promising future in photovoltaics. Owing to their remarkable material properties such as solution processability, nice defect tolerance, broad bandgap tunability, high quantum yields, large refractive index, and strong nonlinear effects, this family of materials has also shown advantages in many other optoelectronic devices including microlasers, photodetectors, waveguides, and metasurfaces. Very recently, the stability of perovskite devices has been improved with the optimization of synthesis methods and device architectures. It is widely accepted that it is the time to integrate all the perovskite devices into a real system. However, for integrated photonic circuits, the shapes and distributions of chemically synthesized perovskites are quite random and not suitable for integration. Consequently, controlled synthesis and the top‐down fabrication process are highly desirable to break the barriers. Herein, the developments of patterning and integration techniques for halide perovskites, as well as the structure/function relationships, are systematically reviewed. The recent progress in the study of optical responses originating from nanostructured perovskites is also presented. Lastly, the challenges and perspective for nanostructured‐perovskite devices are discussed.

A sequential coevaporation technique of Sb₂Se₃ and sulfur powders is developed for the deposition of antimony selenosulfide (Sb₂(S,Se)₃) thin film, from which it is discovered that the interfacial properties, source–substrate distance, and temperature of the substrate conjugatedly affect the structural and electrical properties. The corresponding device delivers a champion efficiency of 8.0% in the vapor‐deposition‐derived alloy‐type Sb₂(S,Se)₃ films.

Abstract

Antimony selenosulfide (Sb₂(S,Se)₃) is an emerging low‐cost, nontoxic solar material with suitable bandgap and high absorption coefficient. Developing effective methods for fabricating high‐quality films would benefit the device efficiency improvement and deepen the fundamental understanding on the optoelectronic properties. Herein, equipment is developed that allows online introduction of precursor vapor during the reaction process, enabling sequential coevaporation of Sb₂Se₃ and S powders for the deposition of Sb₂(S,Se)₃ thin films. With this unique ability, it is revealed that the deposition sequence manipulates both the interfacial properties and optoelectronic properties of the absorber film. A power conversion efficiency of 8.0% is achieved, which is the largest value in vapor‐deposition‐derived Sb₂(S,Se)₃ solar cells. The research demonstrates that multi‐source sequential coevaporation is an efficient technique to fabricate high‐efficiency Sb₂(S,Se)₃ solar cells.

A new molecule, SFIC‐Cl, featured by enhanced π‐electron delocalization by fused‐spiroconjugation and narrowed bandgap by chlorination, is constructed, and is integrated into single‐crystal transistors, organic light‐emitting diodes, and organic photovoltaics. This study demonstrates that these chlorinated spiroconjugated fused systems offer a novel direction toward development of high‐performance organic semiconductor materials for hybrid organic electronic devices.

Abstract

The synthesis of a new molecule, SFIC‐Cl, is reported, which features enhanced π‐electron delocalization by spiroconjugation and narrowed bandgap by chlorination. SFIC‐Cl is integrated into a single‐crystal transistor (OFET) and organic light‐emitting diode (OLED). The material demonstrates remarkable transport abilities across various solution‐processed OFETs and retains efficient radiance in a near‐infrared OLED emitting light at 700 nm. Furthermore, the intermolecular multi‐dimensional connection of SFIC‐Cl enables the fabrication of a single‐component large‐area (2 × 2 cm²) near‐infrared OLED by spin‐coating. The SFIC‐Cl‐acceptor‐based solar cell shows excellent power conversion efficiency of 10.16% resulting from the broadened and strong absorption and well‐matched energy levels. The study demonstrates that chlorinated spiroconjugated fused systems offer a novel direction toward the development of high‐performance organic semiconductor materials for hybrid organic electronic devices.

The mystery of the buried interface in perovskite photovoltaics is deciphered by combining advanced spectroscopy techniques with a lift‐off strategy. The findings open a new avenue to understanding performance losses and thus the design of unique passivation strategies to remove imperfections at the top surfaces and buried interfaces of perovskite photovoltaics, resulting in substantial enhancement in device performance.

Abstract

Understanding the fundamental properties of buried interfaces in perovskite photovoltaics is of paramount importance to the enhancement of device efficiency and stability. Nevertheless, accessing buried interfaces poses a sizeable challenge because of their non‐exposed feature. Herein, the mystery of the buried interface in full device stacks is deciphered by combining advanced in situ spectroscopy techniques with a facile lift‐off strategy. By establishing the microstructure–property relations, the basic losses at the contact interfaces are systematically presented, and it is found that the buried interface losses induced by both the sub‐microscale extended imperfections and lead‐halide inhomogeneities are major roadblocks toward improvement of device performance. The losses can be considerably mitigated by the use of a passivation‐molecule‐assisted microstructural reconstruction, which unlocks the full potential for improving device performance. The findings open a new avenue to understanding performance losses and thus the design of new passivation strategies to remove imperfections at the top surfaces and buried interfaces of perovskite photovoltaics, resulting in substantial enhancement in device performance.

Blending the organic semiconductor 2,7‐dioctyl[1]benzothieno[3,2‐b]benzothiophene (C₈‐BTBT) with the layered Ruddlesden–Popper‐phase perovskite (PEA)₂PbBr₄ in solution phase facilitates the formation of large and near‐single‐crystalline‐quality platelet‐like perovskite domains overlaid by a thin layer of the organic molecule. Transistors utilizing the (PEA)₂PbBr₄/C₈‐BTBT bilayer as the channel exhibit unexpectedly large hysteresis, and their use as a non‐volatile memory element is demonstrated.

Abstract

Controlling the morphology of metal halide perovskite layers during processing is critical for the manufacturing of optoelectronics. Here, a strategy to control the microstructure of solution‐processed layered Ruddlesden–Popper‐phase perovskite films based on phenethylammonium lead bromide ((PEA)₂PbBr₄) is reported. The method relies on the addition of the organic semiconductor 2,7‐dioctyl[1]benzothieno[3,2‐b]benzothiophene (C₈‐BTBT) into the perovskite formulation, where it facilitates the formation of large, near‐single‐crystalline‐quality platelet‐like (PEA)₂PbBr₄ domains overlaid by a ≈5‐nm‐thin C₈‐BTBT layer. Transistors with (PEA)₂PbBr₄/C₈‐BTBT channels exhibit an unexpectedly large hysteresis window between forward and return bias sweeps. Material and device analysis combined with theoretical calculations suggest that the C₈‐BTBT‐rich phase acts as the hole‐transporting channel, while the quantum wells in (PEA)₂PbBr₄ act as the charge storage element where carriers from the channel are injected, stored, or extracted via tunneling. When tested as a non‐volatile memory, the devices exhibit a record memory window (>180 V), a high erase/write channel current ratio (10⁴), good data retention, and high endurance (>10⁴ cycles). The results here highlight a new memory device concept for application in large‐area electronics, while the growth technique can potentially be exploited for the development of other optoelectronic devices including solar cells, photodetectors, and light‐emitting diodes.

Combining the layer‐by‐layer processing method and a ternary strategy, 18.16% efficiency, which is among the highest values reported to date, is achieved in single‐junction organic photovoltaics (OPVs) based on the PM6:BO‐4Cl:BTP‐S2 blend, superior to that (18.03%) of bulk‐heterojunction OPVs, proving that layer‐by‐layer processed ternary OPVs could be a promising approach to high efficiencies.

Abstract

Obtaining a finely tuned morphology of the active layer to facilitate both charge generation and charge extraction has long been the goal in the field of organic photovoltaics (OPVs). Here, a solution to resolve the above challenge via synergistically combining the layer‐by‐layer (LbL) procedure and the ternary strategy is proposed and demonstrated. By adding an asymmetric electron acceptor, BTP‐S2, with lower miscibility to the binary donor:acceptor host of PM6:BO‐4Cl, vertical phase distribution can be formed with donor‐enrichment at the anode and acceptor‐enrichment at the cathode in OPV devices during the LbL processing. In contrast, LbL‐type binary OPVs based on PM6:BO‐4Cl still show bulk‐heterojunction like morphology. The formation of the vertical phase distribution can not only reduce charge recombination but also promote charge collection, thus enhancing the photocurrent and fill factor in LbL‐type ternary OPVs. Consequently, LbL‐type ternary OPVs exhibit the best efficiency of 18.16% (certified: 17.8%), which is among the highest values reported to date for OPVs. The work provides a facile and effective approach for achieving high‐efficiency OPVs with expected morphologies, and demonstrates the LbL‐type ternary strategy as being a promising procedure in fabricating OPV devices from the present laboratory study to future industrial production.

A thermally stable perovskite solar cell is developed by capturing mobile lithium ions using a new molecular hole transporter, 1,3‐bis(5‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)thieno[3,2‐b]thiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (coded HL38), where a strong interaction of the lithium ions in lithium bis(trifluoromethanesulfonyl)imide with the 5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione (octyl‐TPD) moiety in HL38 is responsible for maintaining ≈86% of the initial power conversion efficiency for over 1000 h at 85 °C.

Abstract

A thermally stable perovskite solar cell (PSC) based on a new molecular hole transporter (MHT) of 1,3‐bis(5‐(4‐(bis(4‐methoxyphenyl) amino)phenyl)thieno[3,2‐b]thiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (coded HL38) is reported. Hole mobility of 1.36 × 10⁻³ cm² V⁻¹ s⁻¹ and glass transition temperature of 92.2 °C are determined for the HL38 doped with lithium bis(trifluoromethanesulfonyl)imide and 4‐tert‐butylpyridine as additives. Interface engineering with 2‐(2‐aminoethyl)thiophene hydroiodide (2‐TEAI) between the perovskite and the HL38 improves the power conversion efficiency (PCE) from 19.60% (untreated) to 21.98%, and this champion PCE is even higher than that of the additive‐containing 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐MeOTAD)‐based device (21.15%). Thermal stability testing at 85 °C for over 1000 h shows that the HL38‐based PSC retains 85.9% of the initial PCE, while the spiro‐MeOTAD‐based PSC degrades unrecoverably from 21.1% to 5.8%. Time‐of‐flight secondary‐ion mass spectrometry studies combined with Fourier transform infrared spectroscopy reveal that HL38 shows lower lithium ion diffusivity than spiro‐MeOTAD due to a strong complexation of the Li⁺ with HL38, which is responsible for the higher degree of thermal stability. This work delivers an important message that capturing mobile Li⁺ in a hole‐transporting layer is critical in designing novel MHTs for improving the thermal stability of PSCs. In addition, it also highlights the impact of interface design on non‐conventional MHTs.

Polycrystalline all‐inorganic CsPbI_{3− x} Br _x perovskite exhibits pervasive texture expressions when solution processed into thin‐film optical devices. Synchrotron‐based large‐area X‐ray scattering techniques provide insights, which connect the final texture formation to the crystal symmetry of the halide perovskite, which can be tuned via halide mixing. Both I‐rich and Br‐rich materials each exhibit two different, energetically favored texture directions.

Abstract

Controlling grain orientations within polycrystalline all‐inorganic halide perovskite solar cells can help increase conversion efficiencies toward their thermodynamic limits; however, the forces governing texture formation are ambiguous. Using synchrotron X‐ray diffraction, mesostructure formation within polycrystalline CsPbI_2.85Br_0.15 powders as they cool from a high‐temperature cubic perovskite (α‐phase) is reported. Tetragonal distortions (β‐phase) trigger preferential crystallographic alignment within polycrystalline ensembles, a feature that is suggested here to be coordinated across multiple neighboring grains via interfacial forces that select for certain lattice distortions over others. External anisotropy is then imposed on polycrystalline thin films of orthorhombic (γ‐phase) CsPbI_{3‐ x} Br _x perovskite via substrate clamping, revealing two fundamental uniaxial texture formations; i) I‐rich films possess orthorhombic‐like texture (<100> out‐of‐plane; <010> and <001> in‐plane), while ii) Br‐rich films form tetragonal‐like texture (<110> out‐of‐plane; <110> and <001> in‐plane). In contrast to relatively uninfluential factors like the choice of substrate, film thickness, and annealing temperature, Br incorporation modifies the γ‐CsPbI_{3− x} Br _x crystal structure by reducing the orthorhombic lattice distortion (making it more tetragonal‐like) and governs the formation of the different, energetically favored textures within polycrystalline thin films.

A charge‐transfer complex strategy to reduce the energy disorder of organic semiconductor (OS) charge transport layers (CTLs) by doping a well‐designed OS (BDT‐Si) with electron‐acceptor features in a commercial hole‐transport material (PTAA) is proposed. As a result, the p–i–n planar perovskite solar cells with the optimized hole‐transport layer exhibit the best power conversion efficiency of 21.87%, and good operating stability at maximum power point under continuous illumination.

Abstract

Solution‐processed organic semiconductor charge‐transport layers (OS‐CTLs) with high mobility, low trap density, and energy level alignment have dominated the important progress in p–i–n planar perovskite solar cells (pero‐SCs). Unfortunately, their inevitable long chains result in weak molecular stacking, which is likely to generate high energy disorder and deteriorate the charge‐transport ability of OS‐CTLs. Here, a charge‐transfer complex (CTC) strategy to reduce the energy disorder in the OS‐CTLs by doping an organic semiconductor, 4,4′‐(4,8‐bis(5‐(trimethylsilyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)bis(N,N‐bis(4‐methoxyphenyl)aniline) (BDT‐Si), in a commercial hole‐transport layer (HTL), poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl)amine (PTAA), is proposed. The formation of the CTC makes the PTAA conjugated backbone electron‐deficient, resulting in a quinoidal and stiffer character, which is likely to planarize the PTAA backbone and enhance the ordering of the film in nanoscale. The resultant HTL exhibits a reduced energy disorder, which simultaneously promotes hole transport in the HTL, hole extraction at the interface, energy level alignment, and quasi‐Fermi level splitting in the device. As a result, the p–i–n planar pero‐SCs with optimized HTL exhibit the best power conversion efficiency of 21.87% with good operating stability. This finding demonstrates that the CTC strategy is an effective way to reduce the energy disorder in HTLs and to improve the performance of planar pero‐SCs.