Chen Weijie

Publication date: January 2021

Source: Nano Energy, Volume 79

Author(s): Ming-Hua Li, Tian-Ge Sun, Jiang-Yang Shao, Yu-Duan Wang, Jin-Song Hu, Yu-Wu Zhong

Publication date: January 2021

Source: Nano Energy, Volume 79

Author(s): Huanyu Chen, Faguang Zhou, Zhiwen Jin

Publication date: January 2021

Source: Nano Energy, Volume 79

Author(s): Jinlu He, Wei-Hai Fang, Run Long, Oleg V. Prezhdo

Publication date: January 2021

Source: Nano Energy, Volume 79

Author(s): Shaobing Xiong, Ying Dai, Jianming Yang, Wei Xiao, Danqin Li, Xianjie Liu, Liming Ding, Pingping Gao, Mats Fahlman, Qinye Bao

Publication date: February 2021

Source: Nano Energy, Volume 80

Author(s): Jiabao Li, Jialong Duan, Xiya Yang, Yanyan Duan, Peizhi Yang, Qunwei Tang

Quantum dot thin‐film solar cell has attracted great attention with room for improvement. To achieve high‐efficiency commercial photovoltaic devices, appropriate optical and electrical designs are needed to breakdown the current limitation of quantum dot solar cells. Furthermore, recent approaches for stability and eco‐friendly issues in terms of both materials and structures are discussed.

Abstract

Quantum dots (QDs) are emerging photovoltaic materials that display exclusive characteristics that can be adjusted through modification of their size and surface chemistry. However, designing a QD‐based optoelectronic device requires specialized approaches compared with designing conventional bulk‐based solar cells. In this paper, design considerations for QD thin‐film solar cells are introduced from two different viewpoints: optics and electrics. The confined energy level of QDs contributes to the adjustment of their band alignment, enabling their absorption characteristics to be adapted to a specific device purpose. However, the materials selected for this energy adjustment can increase the light loss induced by interface reflection. Thus, management of the light path is important for optical QD solar cell design, whereas surface modification is a crucial issue for the electrical design of QD solar cells. QD thin‐film solar cell architectures are fabricated as a heterojunction today, and ligand exchange provides suitable doping states and enhanced carrier transfer for the junction. Lastly, the stability issues and methods on QD thin‐film solar cells are surveyed. Through these strategies, a QD solar cell study can provide valuable insights for future‐oriented solar cell technology.

The precise composition of the intermixed phase in bulk heterojunction structures with device‐relevant size is determined via the analysis of the glass transition temperatures proven by fast scanning calorimetry. A relatively small fraction (<15 wt%) of an acceptor in the intermixed amorphous phase leads already to efficient charge generation. However, charge transport can only be sustained in blend morphologies with a significant amount of the acceptor in the intermixed phase (in this case: ≈58 wt%).

Abstract

The relation of phase morphology and solid‐state microstructure with organic photovoltaic (OPV) device performance has intensely been investigated over the last twenty years. While it has been established that a combination of donor:acceptor intermixing and presence of relatively phase‐pure donor and acceptor domains is needed to get an optimum compromise between charge generation and charge transport/charge extraction, a quantitative picture of how much intermixing is needed is still lacking. This is mainly due to the difficulty in quantitatively analyzing the intermixed phase, which generally is amorphous. Here, fast scanning calorimetry, which allows measurement of device‐relevant thin films (<200 nm thickness), is exploited to deduce the precise composition of the intermixed phase in bulk‐heterojunction structures. The power of fast scanning calorimetry is illustrated by considering two polymer:fullerene model systems. Somewhat surprisingly, it is found that a relatively small fraction (<15 wt%) of an acceptor in the intermixed amorphous phase leads to efficient charge generation. In contrast, charge transport can only be sustained in blends with a significant amount of the acceptor in the intermixed phase (in this case: ≈58 wt%). This example shows that fast scanning calorimetry is an important tool for establishing a complete compositional characterization of organic bulk heterojunctions. Hence, it will be critical in advancing quantitative morphology–function models that allow for the rational design of these devices, and in delivering insights in, for example, solar cell degradation mechanisms via phase separation, especially for more complex high‐performing systems such as nonfullerene acceptor:polymer bulk heterojunctions.

A low‐cost industrial organic pigment, quinacridone (QA), was applied as surface passivation agent for perovskite solar cells (PSCs) by solution processing of a soluble QA derivative followed by thermal annealing to convert it into insoluble QA. Passivation with strong interactions between QA molecules and metal halides, together with the hydrophobicity of QA coating, enabled highly efficient PSCs with remarkable stability.

Abstract

Surface passivation of perovskite solar cells (PSCs) using a low‐cost industrial organic pigment quinacridone (QA) is presented. The procedure involves solution processing a soluble derivative of QA, N,N‐bis(tert‐butyloxycarbonyl)‐quinacridone (TBOC‐QA), followed by thermal annealing to convert TBOC‐QA into insoluble QA. With halide perovskite thin films coated by QA, PSCs based on methylammonium lead iodide (MAPbI₃) showed significantly improved performance with remarkable stability. A PCE of 21.1 % was achieved, which is much higher than 18.9 % recorded for the unmodified devices. The QA coating with exceptional insolubility and hydrophobicity also led to greatly enhanced contact angle from 35.6° for the pristine MAPbI₃ thin films to 77.2° for QA coated MAPbI₃ thin films. The stability of QA passivated MAPbI₃ perovskite thin films and PSCs were significantly enhanced, retaining about 90 % of the initial efficiencies after more than 1000 hours storage under ambient conditions.

Nature Energy, Published online: 21 October 2020; doi:10.1038/s41560-020-00725-1

An amphiphilic dendritic block copolymer is developed to serve as an efficient surface modifier of ZnO electron‐transporting layer in an organic photovoltaic device. When using an interlayer based on its hybridization with gold nanoparticles, the device can deliver improved performance and possess a lifetime of over 1.79 years when stored at room temperature in inert conditions.

Abstract

Herein, interfacial engineering is demonstrated to improve the thermal stability of non‐fullerene bulk‐heterojunction (BHJ) OPVs to a practical level. An amphiphilic dendritic block copolymer (DBC) is developed through a facile coupling method and employed as the surface modifier of ZnO electron‐transporting layer in inverted OPVs. Besides showing distinct self‐assembly behavior, the synthesized DBC possesses high compatibility with plasmonic gold nanoparticles (NPs) due to the constituent malonamide and ethylene oxide units. The hybrid DBC@AuNPs interlayer is shown to improve device's performance from 14.0% to 15.4% because it enables better energy‐level alignment and improves interfacial compatibility at the ZnO/BHJ interface. Moreover, the DBC@AuNPs interlayer not only improves the interfacial thermal stability at the ZnO/BHJ interface but also endows a more ideal BHJ morphology with an enhanced thermal robustness. The derived device reserves 77% of initial PCE after thermal aging at 65 °C for 3000 h and yields an extended T ₈₀ lifetime of >1100 h when stored at a constant thermal condition at 65 °C, outperforming the control device. Finally, the device is evaluated to possess a T ₈₀ lifetime of over 1.79 years at room temperature (298 K) when stored in an inert condition, showing great potential for commercialization.

A high‐pressure nitrogen‐extraction strategy to drive the formation of a stable intermediate for uniform perovskite crystallization and an effective passivation strategy by utilizing an ionic liquid are reported. As such, the PCEs of a small‐area PSC and a large‐area PSC module are 22.7% and 19.6% respectively, representing a high level made using a large‐area fabrication process.

Abstract

Slot‐die coating holds advantages over other large‐scale technologies thanks to its potential for well‐controlled, high‐throughput, continuous roll‐to‐roll fabrication. Unfortunately, it is challenging to control thin.film uniformity over a large area while maintaining crystallization quality. Herein, by using a high‐pressure nitrogen‐extraction (HPNE) strategy to assist crystallization, a wide processing window in the well‐controlled printing process for preparing high‐quality perovskites is achieved. The yellow‐phase perovskite generated by the HPNE acts as a crucial intermediate phase to produce large‐area high‐quality perovskite film. Furthermore, an ionic liquid is developed to passivate the perovskite surface to reduce surface defect density and to suppress carrier recombination, resulting in significantly increased efficiency to 22.7%, the highest for large‐area fabrication. The strategies are successfully extended to large‐area device fabrication, making it possible to produce a 40 × 40 mm² module with stabilized PCE as high as 19.4%, the highest‐efficiency for a large‐area module to date.

Dynamic processes of mobile ions, as well as the interaction between charge carriers and mobile ions, are intimately correlated to the observed slow response in perovskites. Photoluminescence (PL) and time‐resolved PL (TRPL) imaging are unique tools to probe the dynamic processes of the slow response and the corresponding microscopic and temporal physical mechanisms.

Abstract

Halide perovskites are promising candidate materials for the next generation high‐efficiency optoelectronic devices. Since perovskites are electronic‐ionic mixed conductors, ion dynamics have a critical impact on the performance and stability of perovskite‐based applications. However, comprehensively understanding ionic dynamics is challenging, particularly on nanoscale imaging of ionic dynamics in perovskites. In this review, mobile ion dynamics in halide perovskites investigated via luminescence spectroscopy combined with confocal microscopy are discussed, including mobile ion induced fluorescence quenching, phase segregation in mixed halide hybrid perovskite, and mobile ion accumulation at the interface in perovskite devices. Steady‐state and time‐resolved luminescence imaging techniques, combined with confocal microscopy, are unique tools for probing ionic dynamics in perovskites, providing invaluable insights on ionic dynamics in nanoscale resolution, along with a wide temporal range from picoseconds to hours. The works in this review are not only for understanding mobile ions to improve the design of perovskite‐based devices but also foster the development of microspectroscopic methodologies in a broader solid‐state physics context of investigating ionic transports in polycrystalline materials.

Nature Materials, Published online: 19 October 2020; doi:10.1038/s41563-020-00826-y

Publication date: 18 November 2020

Source: Joule, Volume 4, Issue 11

Author(s): Kuan Liu, Qiong Liang, Minchao Qin, Dong Shen, Hang Yin, Zhiwei Ren, Yaokang Zhang, Hengkai Zhang, Patrick W.K. Fong, Zehan Wu, Jiaming Huang, Jianhua Hao, Zijian Zheng, Shu Kong So, Chun-Sing Lee, Xinhui Lu, Gang Li