Yingzhi Jin

Solar steam generation at the sterilization condition suffers from low efficiency, especially in passive solar thermal devices. We developed a stationary solar collector with a transparent aerogel layer to achieve efficient solar steam generation via thermal concentration. In field tests performed in Mumbai, India, the device generated steam at 100°C with 56% efficiency and successfully powered a sterilization cycle following the standard sterilization protocol. Our work shows the potential of solar thermal technology in steam generation and other applications.

An additive‐involved leaching method is proposed to reduce the preparation temperature of CsPbI₃ to 100 °C. The CsPbI₃ perovskite film with high crystallinity is formed by an ion exchange reaction between DMAPbI₃ and Cs₄PbI₆. More than 16% photoelectric conversion efficiency can be achieved and the inencapsulation device exhibits remaekable stability.

Abstract

Inorganic CsPbI₃ perovskite with an optical bandgap ranging from 1.67 to 1.75 eV is a promising light‐harvesting material as a top cell in tandem solar cells, but its high fabrication temperature can damage the middle layers or the bottom subcells. Here, an additive‐involved leaching method to fabricate CsPbI₃ perovskite films is demonstrated, which can decrease the preparation temperature to 100 °C. The CsPbI₃ perovskite films with high crystallinity are achieved by a solution assisted reaction between DMAPbI₃ and Cs₄PbI₆ with the leaching of DMA⁺, Cs⁺, and I⁻. The as‐prepared CsPbI₃ perovskite films exhibit much superior stability compared to their high‐temperature counterparts. As a result, a power conversion efficiency of over 16% is obtained, and the unencapsulated device maintains over 93% of the initial efficiency after aging for 30 days in air with a relative humidity of 10%.

In article number 2000842, Valeria Nicolosi, Yuxi Xu, and co‐workers review the commonly used strategies for manufacturing 3D MXene architectures. Special attention is also given to understand the structure‐property relationships of 3D MXene architectures and highlight their promising applications in electrochemical energy storage and conversion, including supercapacitors, rechargeable batteries, and electrocatalysis.

Polymer‐based solid electrolytes (PSEs) have potential to replace liquid electrolytes to realize all‐solid‐state lithium batteries with high safety. This review summarizes some recent prominent advancements in PSEs with regard to polymer matrix selection, architectural engineering of polymers, and properties of different fillers. Application of PSEs in lithium batteries, suppression of lithium dendrites, and flexible batteries are also highlighted.

Abstract

Polymer‐based solid electrolytes (PSEs) have attracted tremendous interests for the next‐generation lithium batteries in terms of high safety and energy density along with good flexibility. Remarkable performances have been demonstrated in PSEs, which endowed PSEs with the potential to replace liquid electrolytes to meet the market demands. In this review, polymer matrices, different polymer architectures, and functional filler materials used in PSEs are discussed to explore the design concepts, methodologies, working mechanisms, and pros and cons of various PSEs. In addition, their recent notable applications in all‐solid‐state lithium ion batteries, lithium–sulfur batteries, suppression of lithium dendrites, and flexible lithium batteries are also introduced. Finally, the challenges and future prospects are sketched to provide strategies to explore novel PSEs for high‐performance all‐solid‐state lithium batteries.

A rational interface engineering strategy is presented for the potassium‐guided grain growth of deep‐blue perovskites with controlled crystal orientation. Efficient and stable perovskite LEDs emitting at 469 nm exhibit an external quantum efficiency of 4.14% and a Commission Internationale de l'Eclairage coordinate of (0.125, 0.076), matching well the National Television System Committee (NTSC) standard blue.

Abstract

Perovskite light‐emitting diodes (PeLEDs) are emerging candidates for the applications of solution‐processed full‐color displays. However, the device performance of deep‐blue PeLED still lags far behind that of their red and green counterparts, which is largely limited by low external quantum efficiency (EQE) and poor operational stability. Here, a facile and reliable crystallization strategy for perovskite grains is proposed, with improved deep‐blue emission through rational interfacial engineering. By modifying the substrate with potassium cation (K⁺) as the supplier of heterogeneous nucleation seeds, the interfacial K⁺‐guided grain growth is realized for well‐packed perovskite assemblies with high surface coverage and the controlled crystal orientation, leading to the enhanced radiative recombination and hole‐transport capabilities. Synergistical boost in device performance is achieved for deep‐blue PeLEDs emitting at 469 nm with a peak EQE of 4.14%, a maximum luminance of 451 cd m^–2, and spectrally stable color coordinates of (0.125, 0.076) that matches well with the National Television System Committee (NTSC) standard blue.

Nature Communications, Published online: 26 November 2020; doi:10.1038/s41467-020-19853-z

Non-fullerene acceptors are crucial for realising efficient charge transport and high power conversion in organic solar cells, yet the relationship of molecular packing and carrier transport is not well-understood. Here, the authors study the effect of side-chain engineering on the backbone assembly and the corresponding charge transport pathway.

Perovskite-silicon tandem solar cells are able to generate higher power conversion efficiencies than market-dominating crystalline-silicon single-junction solar cells and are expected to enter the market in the coming years. Therefore, the optimal tandem architecture needs to be identified and developed. In this modeling work, an in-depth comparison between different tandem architectures is presented. In particular, we focus on the performance of the three-terminal architecture, which, according to our simulations, generates the highest energy yield among the examined tandem architectures.

Non-fullerene solar cells have shown a remarkable development with the device efficiency exceeding 17%. Here, we utilized in-situ measurements, including magnetic field effects of photocurrent and magnetic field effects of polarization, to investigate the charge separation at D:A interfaces at the device-operating condition based on the popular PM6:Y6 non-fullerene system when the PM6 and Y6 components are separately and simultaneously excited. We found that the self-stimulated dissociation is essentially enabled by optically induced bulk polarization in non-fullerene acceptor-Y6 molecules.

Great progress has been made in the field of inorganic CsPbX₃ perovskite solar cells (PSCs), and organic molecule engineering has been playing a vital role in improving device performance. In this review, the roles of organic molecules in inorganic CsPbX₃ PSCs are systematically reviewed and discussed, and future research directions are suggested to further improve the performance of inorganic PSCs.

Abstract

Over 25% efficiencies have been achieved by organic–inorganic hybrid perovskite solar cells (PSCs). However, their practical applications are limited by the instability of the hybrid perovskite materials. Replacing hybrid perovskites with inorganic CsPbX₃ perovskites shows great promise to address the above issue and much progress has been made. To achieve high efficiency and stable inorganic CsPbX₃ PSCs, organic molecular engineering has been playing a vital role. Herein, the progress of the organic molecular engineering in inorganic CsPbX₃ PSCs is systematically reviewed. First, structure evolution induced by organic molecular engineering for inorganic CsPbX₃ perovskites is demonstrated. Then, organic molecular engineering in CsPbX₃ PSCs is categorized and reviewed (alloying in perovskite structures, as sacrificial agents, forming 2D structures, and modifying surfaces and interfaces). Finally, future research directions are suggested to further improve the performance of inorganic PSCs.

Photoinduced degradation can happen in each functional layer in perovskite solar cells, including the active layer, electronic transport layer, hole transport layer and their interfaces. An overview of these degradation categories and the corresponding solutions is proposed in this review, in the hope of encouraging further research and optimization of the devices.

Abstract

Solar cells based on metal halide perovskites have reached a power conversion efficiency as high as 25%. Their booming efficiency, feasible processability, and good compatibility with large‐scale deposition techniques make perovskite solar cells (PSCs) desirable candidates for next‐generation photovoltaic devices. Despite these advantages, the lifespans of solar cells are far below the industry‐needed 25 years. In fact, numerous PSCs throughout the literature show severely hampered stability under illumination. Herein, several photoinduced degradation mechanisms are discussed. With light radiation, the organic–inorgainc perovskites are prone to phase segregation or chemical decomposition; the oxide electron transport layers (ETLs) tend to introduce new defects at the interface; the commonly used small molecules‐based hole transport layers (HTLs) typically suffer from poor photostability and dopant diffusion during device operation. It has been demonstrated the photoinduced degradation can take place in every functional layer, including the active layer, ETL, HTL, and their interfaces. An overview of these degradation categories is provided in this review, in the hope of encouraging further research and optimization of relevant devices.

A series of PM6 polymers with different weight‐average molecular weights and polydispersity index are synthesized, and the effects of PM6 polymerization degree on the efficiency and degradation behaviors of the Y6‐based photovoltaic system are systematically studied.

Abstract

The degree of polymerization can cause significant changes in the blend microstructure and physical mechanism of the active layer of non‐fullerene polymer solar cells, resulting in a huge difference in device performance. However, the diversity of stability issues, including photobleaching stability, storage stability, photostability, thermal stability, and mechanical stability, and more, poses a challenge for the degree of polymerization to comprehensively address the trade‐off between device efficiency and stability and reasonably evaluate the application potential of polymer materials. Herein, a series of PM6 polymers with different weight‐average molecular weights (M _w) and polydispersity index (PDI) are synthesized. The effects of the degree of PM6 polymerization on the efficiency and degradation behaviors of the photovoltaic systems based on Y6 as acceptor are investigated systematically. The findings regarding stability issues, together with the trade‐offs in the efficiency‐stability gap, formulate a complete guideline for the material design and performance evaluation in a way that relies much less on trial‐and‐error efforts.

The present work deconvolutes the electronic processes in organic solar cells under short‐circuit conditions by combining readily available experimental methods (current‐voltage characteristics, external quantum efficiency) with optical simulations. The proposed method allows the quantification of geminate recombination, to determine the mobility‐lifetime product, and to quantify extraction. The applicability of this new approach is demonstrated in three different organic photovoltaic systems.

Abstract

The short‐circuit current (J _sc) of organic solar cells is defined by the interplay of exciton photogeneration in the active layer, geminate and non‐geminate recombination losses and free charge carrier extraction. The method proposed in this work allows the quantification of geminate recombination and the determination of the mobility‐lifetime product (µτ) as a single integrated parameter for charge transport and non‐geminate recombination. Furthermore, the extraction efficiency is quantified based on the obtained µτ product. Only readily available experimental methods (current‐voltage characteristics, external quantum efficiency measurements) are employed, which are coupled with an optical transfer matrix method simulation. The required optical properties of common organic photovoltaic (OPV) materials are provided in this work. The new approach is applied to three OPV systems in inverted or conventional device structures, and the results are juxtaposed against the µτ values obtained by an independent method based on the voltage–capacitance spectroscopy technique. Furthermore, it is demonstrated that the new method can accurately predict the optimal active layer thickness.

Herein, how F, OH, and O mix terminations affect the work function of the Ti₃C₂/MAPbI₃ interface is studied, covering the whole phase‐space of mixtures and highlighting the mechanism of strong nonlinear behaviors. Using first‐principles calculations, the degree and origin of the work function non‐linearity is described and sized.

Abstract

MXenes are a recent family of 2D materials with very interesting electronic properties for device applications. One very appealing feature is the wide range of work functions shown by these materials, depending on their composition and surface terminations, that can be exploited to adjust band alignments between different material layers. In this work, based on density functional theory calculations, how mixed terminations of F, OH, and/or O affect the work function of Ti₃C₂ MXene is analyzed in detail, covering the whole phase‐space of mixtures. The Ti₃C₂/CH₃NH₃PbI₃ (MAPbI₃) perovskite coupled system for solar cell applications is also analyzed. A strong nonlinear behavior is found when varying the relative concentrations of OH, O, and F terminations, with the strongest effect of the OH groups in lowering the work function, already at a relative amount of 25%. A surprising minimum work function is found for relative OH:O fraction of 75:25, explained in terms of the nonlinear electronic response in screening the surface dipoles.

The surface functionalization of 2D materials is critical for tuning properties and application performance. In the case of MXenes, oxygen‐terminated surfaces are critical for applications in energy storage and catalysis. Here, a route for exclusively functionalizing MXene surfaced by oxygen is shown and pushed to the limit.

Abstract

Tuning and tailoring of surface terminating functional species hold the key to unlock unprecedented properties for a wide range of applications of the largest 2D family known as MXenes. However, a few routes for surface tailoring are explored and little is known about the extent to which the terminating species can saturate the MXene surfaces. Among available terminations, atomic oxygen is of interest for electrochemical energy storage, hydrogen evolution reaction, photocatalysis, etc. However, controlled oxidation of the surfaces is not trivial due to the favored formation of oxides. In the present contribution, single sheets of Ti₃C₂T _x MXene, inherently terminated by F and O, are defluorinated by heating in vacuum and subsequentially exposed to O₂ gas at temperatures up to 450 °C in situ, in an environmental transmission electron microscope. Results include exclusive termination by O on the MXene surfaces and eventual supersaturation (x > 2) with a retained MXene sheet structure. Upon extended O exposure, the MXene structure transforms into TiO₂ and desorbs surface bound H₂O and CO₂ reaction products. These results are fundamental for understanding the oxidation, the presence of water on MXene surfaces, and the degradation of MXenes, and pave way for further tailoring of MXene surfaces.

Polymer‐based solid electrolytes (PSEs) have potential to replace liquid electrolytes to realize all‐solid‐state lithium batteries with high safety. This review summarizes some recent prominent advancements in PSEs with regard to polymer matrix selection, architectural engineering of polymers, and properties of different fillers. Application of PSEs in lithium batteries, suppression of lithium dendrites, and flexible batteries are also highlighted.

Abstract

Polymer‐based solid electrolytes (PSEs) have attracted tremendous interests for the next‐generation lithium batteries in terms of high safety and energy density along with good flexibility. Remarkable performances have been demonstrated in PSEs, which endowed PSEs with the potential to replace liquid electrolytes to meet the market demands. In this review, polymer matrices, different polymer architectures, and functional filler materials used in PSEs are discussed to explore the design concepts, methodologies, working mechanisms, and pros and cons of various PSEs. In addition, their recent notable applications in all‐solid‐state lithium ion batteries, lithium–sulfur batteries, suppression of lithium dendrites, and flexible lithium batteries are also introduced. Finally, the challenges and future prospects are sketched to provide strategies to explore novel PSEs for high‐performance all‐solid‐state lithium batteries.

A rational interface engineering strategy is presented for the potassium‐guided grain growth of deep‐blue perovskites with controlled crystal orientation. Efficient and stable perovskite LEDs emitting at 469 nm exhibit an external quantum efficiency of 4.14% and a Commission Internationale de l'Eclairage coordinate of (0.125, 0.076), matching well the National Television System Committee (NTSC) standard blue.

Abstract

Perovskite light‐emitting diodes (PeLEDs) are emerging candidates for the applications of solution‐processed full‐color displays. However, the device performance of deep‐blue PeLED still lags far behind that of their red and green counterparts, which is largely limited by low external quantum efficiency (EQE) and poor operational stability. Here, a facile and reliable crystallization strategy for perovskite grains is proposed, with improved deep‐blue emission through rational interfacial engineering. By modifying the substrate with potassium cation (K⁺) as the supplier of heterogeneous nucleation seeds, the interfacial K⁺‐guided grain growth is realized for well‐packed perovskite assemblies with high surface coverage and the controlled crystal orientation, leading to the enhanced radiative recombination and hole‐transport capabilities. Synergistical boost in device performance is achieved for deep‐blue PeLEDs emitting at 469 nm with a peak EQE of 4.14%, a maximum luminance of 451 cd m^–2, and spectrally stable color coordinates of (0.125, 0.076) that matches well with the National Television System Committee (NTSC) standard blue.

It is found that the dynamic redistribution of mobile ions modifies the injection and transport property of charge carriers in the emissive layer, which can well explain the hysteresis in external quantum efficiency (EQE)– and radiance–voltage curves, as well as the rise phenomena of EQE and radiance under low constant driving voltages.

Abstract

Despite quick development of perovskite light‐emitting diodes (PeLEDs) during the past few years, the fundamental mechanisms on how ion migration affects device efficiency and stability remain unclear. Here, it is demonstrated that the dynamic redistribution of mobile ions in the emissive layer plays a key role in the performance of PeLEDs and can explain a range of abnormal behaviours commonly observed during the device measurement. The dynamic redistribution of mobile ions changes charge–carrier injection and leads to increased recombination current; at the same time, the ion redistribution also changes charge transport and results in decreased shunt resistance current. As a result, the PeLEDs show hysteresis in external quantum efficiencies (EQEs) and radiance, that is, higher EQEs and radiance during the reverse voltage scan than during the forward scan. In addition, the changes on charge injection and transport induced by the ion redistribution also well explain the rise of the EQE/radiance values under constant driving voltages. The argument is further rationalized by adding extra formamidinium iodide (FAI) into optimized PeLEDs based on FAPbI₃, resulting in more significant hysteresis and shorter operational stability of the PeLEDs.

A promising path is suggested for upscaling of organic photovoltaics (OPV) toward true mass application in the form of semi‐transparent OPV embedded in polytunnels or green‐houses. Here their specific properties, that is, offering narrow band absorption in the infrared wavelength range can be used as game changer.

Abstract

This Essay presents a possible pathway for the advancement of organic photovoltaics toward broader commercial success and enlarged market size. This vision aims at broad scale applications in photovoltaic greenhouses and polytunnels, which harvest those portions of the solar spectrum that are not used or required by plants. Based on the assumptions of the Shockley–Queisser–Limit, respectively detailed balance, and the additional postulation of using no absorption in the visible part of the AM 1.5G solar spectrum a power conversion efficiency of ≈17% is theoretically predicted. The suggestion is supported by the existence of a number of organic compounds, which already exhibit a good spectral compatibility with the typical photosynthetic action spectrum of chloroplasts. It is hoped that more suitable materials development shall be triggered and fertilized as a result of this Essay.

A series of Donor–π–Acceptor porphyrins coded as CS0, CS1, and CS2 that can effectively passivate the perovskite surface, increase V _OC and FF, reduce the hysteresis effect, enhance power conversion efficiency to be higher than 22%, and improve the device stability have been developed.

Abstract

In recent years, hybrid perovskite solar cells (PSCs) have attracted much attention owing to their low cost, easy fabrication, and high photoelectric conversion efficiency. Nevertheless, solution‐processed perovskite films usually show substantial structural disorders, resulting in ion defects on the surface of lattice and grain boundaries. Herein, a series of D–π–A porphyrins coded as CS0, CS1, and CS2 that can effectively passivate the perovskite surface, increase V _OC and FF, reduce the hysteresis effect, enhance power conversion efficiency to be higher than 22%, and improve the device stability is developed. The results in this study demonstrated that the donor–π–acceptor type porphyrin derivatives are promising passivators that can improve the cell performance of PSCs.

Apart from exciton–phonon coupling, octahedral distortion is revealed to significantly affect the exciton diffusion process. A simple fluorine substitution to phenethylammonium for the organic cations to tune the structural rigidity and octahedral distortion yields a record exciton diffusivity of 1.91 cm² s⁻¹ and a diffusion length of 405 nm along the in‐plane direction.

Abstract

Layered perovskites have been employed for various optoelectronic devices including solar cells and light‐emitting diodes for improved stability, which need exciton transport along both the in‐plane and the out‐of‐plane directions. However, it is not clear yet what determines the exciton transport along the in‐plane direction, which is important to understand its impact toward electronic devices. Here, by employing both steady‐state and transient photoluminescence mapping, it is found that in‐plane exciton diffusivities in layered perovskites are sensitive to both the number of layers and organic cations. Apart from exciton–phonon coupling, the octahedral distortion is revealed to significantly affect the exciton diffusion process, determined by temperature‐dependent photoluminescence, light‐intensity‐dependent time‐resolved photoluminescence, and density function theory calculations. A simple fluorine substitution to phenethylammonium for the organic cations to tune the structural rigidity and octahedral distortion yields a record exciton diffusivity of 1.91 cm² s⁻¹ and a diffusion length of 405 nm along the in‐plane direction. This study provides guidance to manipulate exciton diffusion by modifying organic cations in layered perovskites.