Chen Weijie

Gradient 1D/3D perovskite bilayer using 4-tert-butylpyridinium cation (TBP⁺) as a cation for 1D perovskite layer is introduced. The crystal structure and fundamental properties of 1D perovskite (TBPPbI₃) are investigated. Gradient 1D/3D perovskite-based devices show an improved power conversion efficiency from 18.3% to 19.3% due to the enhanced hole extraction process and suppressed carrier recombination.

To achieve both high efficiency and long-term stability of perovskite solar cells (PSCs), it is effective to use a perovskite layer in which a low-dimensional perovskite layer is stacked on a 3D perovskite layer. However, the guidelines for the effective structure of these perovskite layers remain unclear. Herein, the gradient structured 1D perovskite layer formed on top of a 3D perovskite layer using 4-tert-butylpyridinium iodide (TBPI) as a capping layer is introduced. It is demonstrated that the gradient structured 1D perovskite layer on the 3D perovskite improves the conversion efficiency of PSCs despite the lateral orientation of the (PbI₃ ⁻) _n linear chain of the 1D perovskite, which is responsible for electronic conduction. In addition, it is found that the hydrophobic organic unit of TBPI protects the 3D perovskite layer, which enhances its long-term stability.

Perovskite solar cells in which H₂-phthalocyanine is introduced as a hole transport material showed superior thermal long-term stability and improved performance over the 20%. These results are driven by a surface passivation of hybrid halide perovskites with H₂-phthalocyanine as a Lewis base.

Abstract

Perovskite solar cells in an n-i-p structure record high power conversion efficiency, but issues of insufficient thermal stability and the high cost of p-type hole transporting materials have been raised as drawbacks. H₂-phthalocyanine (Pc) is introduced as a hole transport material to ensure the thermal stability and simultaneously have served surface passivation effects on hybrid halide perovskites as a Lewis base. Pyrrolic nitrogen in the Pc reacts with uncoordinated Pb²⁺ ions on the perovskite surface. Upon enhancing the interfacial interaction between phthalocyanine and the perovskite, the open circuit voltage in devices increases as compared to that of devices using a metal-phthalocyanine complex. While the phthalocyanine-applied device maintains superior thermal long-term stability, the power conversion efficiency also exceeds 20%.

This work presents a comprehensive review on the current understanding, and apparent contradictions, of experimental observation, interpretation, and theoretical hypotheses presented in the state-of-the-art mixed dimensional 2D-3D perovskite literature and identifies promising future research directions for enhancing the stability and performance of such devices.

Abstract

Perovskite solar cells are a potential game changer for the photovoltaics industry, courtesy of their facile fabrication and high efficiency. Despite this, commercialization is being held back by poor stability. To become economically feasible for commercial production, perovskite solar cells must meet or exceed industry standards for operational lifetime and reliability. In this regard, mixed dimensional 2D-3D perovskite solar cells, incorporating long carbon-chain organic spacer cations, have shown promising results, with enhancement in both device efficiency and stability. Dimensional engineering of perovskite films requires a delicate balance of 2D and 3D perovskite composition to take advantage of the specific properties of each material phase. This review summarizes and assesses the current understanding, and apparent contradictions in the state-of-the-art mixed dimensional perovskite solar cell literature regarding the origin of stability and performance enhancement. By combining and comparing results from experimental and theoretical studies it is focused on how the perovskite composition, film formation methods, additive and solvent engineering influence efficiency and stability, and identify future research directions to further improve both key performance metrics.

In this study, the importance of terminal group match in the design of polymer donor and small-molecule acceptor for optimal blend morphology, reduced voltage loss, and high device performances are demonstrated.

Abstract

As a variety of non-fullerene small molecule acceptors (SMAs) have been developed to improve power conversion efficiency (PCE) of organic solar cells (OSCs), the pairing of the SMAs with optimal polymer donors (P _Ds) is an important issue. Herein, a systematic investigation is conducted with the development of the SMA series, named C6OB-H, C6OB-Me, and C6OB-F, which contain distinctive terminal substituents –H, –CH₃, and –F, respectively. These SMAs are paired with two P _Ds, PBDT-H and PBDT-F. Interestingly, the P _D/SMA pairs with similar terminal groups yield enhanced molecular compatibility and energetic interactions, which suppress voltage loss while improving blend morphology to enhance simultaneously the open–circuit voltage, short–circuit current, and fill factor of the OSCs. In particular, the OSC based on the PBDT-F:C6OB-F blend sharing fluorine terminal groups achieves the highest PCE of 15.2%, which outperforms those of PBDT-H:C6OB-F (10.1%) and PBDB-F:C6OB-H OSCs (11.2%). Furthermore, the PBDT-F:C6OB-F OSC maintains high PCEs with active layer thicknesses between 85 and 310 nm. In contrast, the PCE of PBDT-H:C6OB-F-based OSC already drops by 80% from 10.1% to 2.1% when the active layer thickness increases from 100 to 200 nm. This study establishes an important P _D/SMA pairing rule in terms of terminal functional groups for achieving high-performance OSC.

A new series of conjugated molecules with spatially 2D sidechains are designed and utilized as the non-fullerene acceptors in all-small-molecule organic solar cells. The multi-dimensional lamellar packing induced by the orthogonal sidechains is able to tune the morphology as effective as the stacking of conjugated backbones, thus providing an impressive power conversion efficiency of 15.67%.

Abstract

Organic semiconductors consist of a conjugated backbone and flexible sidechains. Compared to the meticulous design of backbones, less attention has been paid to the investigation of sidechains, in particular their spatial orientation. Herein, three non-fullerene acceptors, anti-PDFC, syn-PDFC, and PDFC-Ph, are applied in all-small-molecule organic solar cells (ASM-OSCs) to reveal the varied effects of sidechains on morphology and device performance. With spatially orthogonal alkyl chains, anti-PDFC and syn-PDFC show unique bimodal lamellar packing and moderate crystallinity. When blending with an efficient binary BTR-Cl/Y6 system, anti-PDFC as well as syn-PDFC not only form their own crystal phase but also improve the packing order of BTR-Cl, consequently enhancing the power conversion efficiency (PCE) of ternary ASM-OSC to be 14.56%. However, although PDFC-Ph has an identical backbone with anti-PDFC, the alternated sidechains make it relatively amorphous, which is prone to damage the original packing of the host donor/acceptor, and thus deteriorating the device performance. When PC₇₁BM is added to optimize the morphology further, the triple-acceptor device involving anti-PDFC realizes a PCE of 15.67%, which is among the best efficiencies in ASM-OSCs. This study demonstrates that a multi-dimensional sidechain can optimize the morphology of a bulk heterojunction as effective as a conjugated backbone.

Based on the synergistic effect of the higher dielectric property of non-fullerene acceptors and corresponding photoactive films and the energy transfer from donor to acceptor on charge separation of selected non-fullerene-based photovoltaic devices, these results well interpret the high device performance with a tiny driving force, and the intrinsic physical working mechanism on non-fullerene-based photovoltaic devices is proposed.

Abstract

In non-fullerene-based photovoltaic devices, it is unclear how excitons efficiently dissociate into charge carriers under small driving force. Here, we developed a modified method to estimate dielectric constants of PM6 donor and non-fullerene acceptors. Surprisingly, most non-fullerene acceptors and blend films showed higher dielectric constants. Moreover, they exhibited larger dielectric constants differences at the optical frequency. These results are likely bound to reduced exciton binding energy and bimolecular recombination. Besides, the overlap between the emission spectrum of donor and absorption spectra of non-fullerene acceptors allowed the energy transfer from donor to acceptors. Hence, based on the synergistic effect of dielectric property and energy transfer resulting in efficient charge separation, our finding paves an alternative path to elucidate the physical working mechanism in non-fullerene-based photovoltaic devices.

Publication date: 19 May 2021

Source: Joule, Volume 5, Issue 5

Author(s): Wenyan Yang, Wei Wang, Yuheng Wang, Rui Sun, Jie Guo, Hongneng Li, Mumin Shi, Jing Guo, Yao Wu, Tao Wang, Guanghao Lu, Christoph J. Brabec, Yongfang Li, Jie Min

A new urea-ammonium thiocyanate (UAT) molten salt was introduced as the additive in all-inorganic cesium lead triiodide solar cell, as a modification strategy to fully release and exploit coordination activities of SCN⁻ to deposit high-quality CsPbI₃ film. Thus, the UAT-based devices can provide an encouraging PCE up to 20.08 % with excellent operational stability of over 1000 h.

Abstract

Besides widely used surface passivation, engineering the film crystallization is an important and more fundamental route to improve the performance of all-inorganic perovskite solar cells. Herein, we have developed a urea-ammonium thiocyanate (UAT) molten salt modification strategy to fully release and exploit coordination activities of SCN⁻ to deposit high-quality CsPbI₃ film for efficient and stable all-inorganic solar cells. The UAT is derived by the hydrogen bond interactions between urea and NH₄ ⁺ from NH₄SCN. With the UAT, the crystal quality of the CsPbI₃ film has been significantly improved and a long single-exponential charge recombination lifetime of over 30 ns has been achieved. With these benefits, the cell efficiency has been promoted to over 20 % (steady-state efficiency of 19.2 %) with excellent operational stability over 1000 h. These results demonstrate a promising development route of the CsPbI₃ related photoelectric devices.

An easily synthesized building block BNT and a relevant polymer PBNT‐BDD featuring B‐N covalent bond were synthesized for application in solar cells. The polymer offered a power conversion efficiency of 16.1 %, a nonradiative recombination energy loss of 0.19 eV, and a singlet‐triplet gap as low as 0.15 eV, demonstrating the promising prospect of B‐N‐containing materials in organic photovoltaics.

Abstract

High‐efficiency organic solar cells (OSCs) largely rely on polymer donors. Herein, we report a new building block BNT and a relevant polymer PBNT‐BDD featuring B‐N covalent bond for application in OSCs. The BNT unit is synthesized in only 3 steps, leading to the facile synthesis of PBNT‐BDD. When blended with a nonfullerene acceptor Y6‐BO, PBNT‐BDD afforded a power conversion efficiency (PCE) of 16.1 % in an OSC, comparable to the benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐based counterpart. The nonradiative recombination energy loss of 0.19 eV was afforded by PBNT‐BDD. PBNT‐BDD also exhibited weak crystallinity and appropriate miscibility with Y6‐BO, benefitting of morphological stability. The singlet–triplet gap (ΔE _ST) of PBNT‐BDD is as low as 0.15 eV, which is much lower than those of common organic semiconductors (≥0.6 eV). As a result, the triplet state of PBNT‐BDD is higher than the charge transfer (CT) state, which would suppress the recombination via triplet state effectively.

Ion exchange lithography (IEL) for integrating user-defined patterns of desirable chemical compositions in thin films is introduced. In IEL, a reactive nanoparticle “canvas” is locally converted by printing ion exchange “inks”. The proof-of-concept and versatility are demonstrated by printing, painting, and airbrushing inks to create perovskite semiconductors with tunable composition. The functional potential is explored by fabricating light-emitting diodes.

Abstract

Patterning materials with different properties in a single film is a fundamental challenge and essential for the development of next-generation (opto)electronic functional components. This work introduces the concept of ion exchange lithography and demonstrates spatially controlled patterning of electrically insulating films and semiconductors with tunable optoelectronic properties. In ion exchange lithography, a reactive nanoparticle “canvas” is locally converted by printing ion exchange “inks.” To demonstrate the proof of principle, a canvas of insulating nanoporous lead carbonate is spatioselectively converted into semiconducting lead halide perovskites by contact printing an ion exchange precursor ink of methylammonium and formamidinium halides. By selecting the composition of the ink, the photoluminescence wavelength of the perovskite semiconductors is tunable over the entire visible spectrum. A broad palette of conversion inks can be applied on the reactive film by printing with customizable stamp designs, spray-painting with stencils, and painting with a brush to inscribe well-defined patterns with tunable optoelectronic properties in the same canvas. Moreover, the optoelectronic properties of the converted canvas are exploited to fabricate a green light-emitting diode (LED), demonstrating the functionality potential of ion exchange lithography.

Nature Energy, Published online: 12 April 2021; doi:10.1038/s41560-021-00805-w

The work presents a detailed understanding of solution-processing-dependent quantum well growth and its impact on charge transport and photovoltaic performance for Dion–Jacobson perovskite. Faster solvent removal during film formation leads to a gradient distribution of the quantum wells and a preferential perpendicular orientation. The highest efficiency of 15.81% for aromatic spacer-based Dion–Jacobson perovskite solar cells is achieved.

Abstract

Dion–Jacobson (DJ) 2D hybrid perovskite semiconductors offer improved environmental stability and higher structural diversity in comparison with their 3D analogous. However, lacking of controlled perovskite crystallization makes it a challenge to achieve high charge transport for photovoltaic devices. Here, a detailed understanding of effects on film formation during different solution-casting processes for the DJ perovskite (PDMA)(MA) _{n −1}Pb _n I_{3 n +1} (<n> = 4, PDMA refers to 1,4-phenylenedimethanammonium) in the final film structure and photovoltaic outcomes is presented. Faster removal of solvent from solution via hot-casting or antisolvent dripping results in a more uniform thickness distribution of quantum wells. This eventually enhances carrier transport greatly along perpendicular direction and increases power conversion efficiencies. A high efficiency of 15.81% is achieved for the hot-casting devices, which is also the highest for aromatic spacer-based DJ perovskite solar cells. This work helps to better understand the control of film formation during solution-casting for high performance solar cells.

Nature Energy, Published online: 08 April 2021; doi:10.1038/s41560-021-00802-z

Nature Communications, Published online: 01 April 2021; doi:10.1038/s41467-021-22193-1

Publication date: July 2021

Source: Nano Energy, Volume 85

Author(s): Tanya Kumari, Jiyeon Oh, Sang Myeon Lee, Mingyu Jeong, Jungho Lee, Byongkyu Lee, So-Huei Kang, Changduk Yang

Publication date: July 2021

Source: Nano Energy, Volume 85

Author(s): Jianxing Xia, Ruiling Zhang, Junsheng Luo, Hua Yang, Hongyu Shu, Haseeb Ashraf Malik, Zhongquan Wan, Yu Shi, Keli Han, Ruilin Wang, Xiaojun Yao, Chunyang Jia

Publication date: July 2021

Source: Nano Energy, Volume 85

Author(s): Cheng Chen, Tongtong Xuan, Wenhao Bai, Tianliang Zhou, Fan Huang, An Xie, Le Wang, Rong-Jun Xie

Two new orange–red thermally activated delayed fluorescence (TADF) materials, PzTDBA and PzDBA, are developed based on the acceptor–donor–acceptor configuration. The TADF devices fabricated with 5 wt% PzTDBA and PzDBA as emitting dopants show maximum external quantum efficiency (EQE) of 30.3% and 21.8% with extremely low roll‐off of 3.6% and 3.2% at 1000 cd m⁻². The high efficiency and low roll‐off is due to the high photoluminescence quantum yield (PLQY) and short delayed exciton lifetime.

Abstract

Two new orange–red thermally activated delayed fluorescence (TADF) materials, PzTDBA and PzDBA, are reported. These materials are designed based on the acceptor–donor–acceptor (A–D–A) configuration, containing rigid boron acceptors and dihydrophenazine donor moieties. These materials exhibit a small ΔE _ST of 0.05–0.06 eV, photoluminescence quantum yield (PLQY) as high as near unity, and short delayed exciton lifetime (τ_d) of less than 2.63 µs in 5 wt% doped film. Further, these materials show a high reverse intersystem crossing rate (k _risc) on the order of 10⁶ s⁻¹. The TADF devices fabricated with 5 wt% PzTDBA and PzDBA as emitting dopants show maximum EQE of 30.3% and 21.8% with extremely low roll‐off of 3.6% and 3.2% at 1000 cd m⁻² and electroluminescence (EL) maxima at 576 nm and 595 nm, respectively. The low roll‐off character of these materials is analyzed by using a roll‐off model and the exciton annihilation quenching rates are found to be suppressed by the fast k _risc and short delayed exciton lifetime. These devices show operating device lifetimes (LT₅₀) of 159 and 193 h at 1000 cd m⁻² for PzTDBA and PzDBA, respectively. The high efficiency and low roll‐off of these materials are attributed to the good electronic properties originatng from the A–D–A molecular configuration.

Wide-bandgap oxide semiconductors uniquely combine electrical conductivity and optical transparency and are widely used in optoelectronic devices. The materials physics of wide-bandgap oxide semiconductors, the recent progress in the design of new materials and novel thin-film transistor (TFT) devices, and current challenges and perspectives are reviewed.

Abstract

Wide bandgap oxide semiconductors constitute a unique class of materials that combine properties of electrical conductivity and optical transparency. They are being widely used as key materials in optoelectronic device applications, including flat-panel displays, solar cells, OLED, and emerging flexible and transparent electronics. In this article, an up-to-date review on both the fundamental understanding of materials physics of oxide semiconductors, and recent research progress on design of new materials and high-performing thin film transistor (TFT) devices in the context of fundamental understanding is presented. In particular, an in depth overview is first provided on current understanding of the electronic structures, defect and doping chemistry, optical and transport properties of oxide semiconductors, which provide essential guiding principles for new material design and device optimization. With these principles, recent advances in design of p-type oxide semiconductors, new approaches for achieving cost-effective transparent (flexible) electrodes, and the creation of high mobility 2D electron gas (2DEG) at oxide surfaces and interfaces with a wealth of fascinating physical properties of great potential for novel device design are then reviewed. Finally, recent progress and perspective of oxide TFT based on new oxide semiconductors, 2DEG, and low-temperature solution processed oxide semiconductor for flexible electronics will be reviewed.

Reducing and mitigating non‐radiative recombination defects in perovskite materials are still crucial prerequisites for achieving high performance in light‐emitting applications. Ethoxylated trimethylolpropane triacrylate is introduced in antisolvent to passivate surface and bulk defects during the spinning process, and external quantum efficiency of quasi‐2D perovskite light‐emitting diodes as high as 22.49% is demonstrated.

Abstract

Perovskite light‐emitting diodes (PeLEDs) are considered as particularly attractive candidates for high‐quality lighting and displays, due to possessing the features of wide gamut and real color expression. However, most PeLEDs are made from polycrystalline perovskite films that contain a high concentration of defects, including point and extended imperfections. Reducing and mitigating non‐radiative recombination defects in perovskite materials are still crucial prerequisites for achieving high performance in light‐emitting applications. Here, ethoxylated trimethylolpropane triacrylate (ETPTA) is introduced as a functional additive dissolved in antisolvent to passivate surface and bulk defects during the spinning process. The ETPTA can effectively decrease the charge trapping states by passivation and/or suppression of defects. Eventually, the perovskite films that are sufficiently passivated by ETPTA make the devices achieve a maximum external quantum efficiency (EQE) of 22.49%. To our knowledge, these are the most efficient green PeLEDs up to now. In addition, a threefold increase in the T ₅₀ operational time of the devices was observed, compared to control samples. These findings provide a simple and effective strategy to make highly efficient perovskite polycrystalline films and their optoelectronics devices.

The lithium–sulfur battery is the frontrunner technology for potential large-scale energy storage stemming from its high specific energy capacity and superior energy density. The transition metals, metal dichalcogenides, metal phosphides, metal oxides, metal carbides, metal nitrides, and others (e.g., metal phosphosulfides, metal hydroxides, metal–organic frameworks and hybrids), which can serve as robust cathodes for high-performance Li–S batteries, are presented.

Abstract

Lithium–sulfur (Li-S) batteries have a high specific energy capacity and density of 1675 mAh g⁻¹ and 2670 Wh kg⁻¹, respectively, rendering them among the most promising successors for lithium-ion batteries. However, there are myriads of obstacles in the practical application and commercialization of Li-S batteries, including the low conductivity of sulfur and its discharge products (Li₂S/Li₂S₂), volume expansion of sulfur electrode, and the polysulfide shuttle effect. Hence, immense attention has been devoted to rectifying these issues, of which the application of metal-based compounds (i.e., transition metal, metal phosphides, sulfides, oxides, carbides, nitrides, phosphosulfides, MXenes, hydroxides, and metal-organic frameworks) as sulfur hosts is profiled as a fascinating strategy to hinder the polysulfide shuttle effect stemming from the polar–polar interactions between the metal compounds and polysulfides. This review encompasses the fundamental electrochemical principles of Li-S batteries and insights into the interactions between the metal-based compounds and the polysulfides, with emphasis on the intimate structure–activity relationship corroborated with theoretical calculations. Additionally, the integration of conductive carbon-based materials to ameliorate the existing adsorptive abilities of the metal-based compound is systematically discussed. Lastly, the challenges and prospects toward the smart design of catalysts for the future development of practical Li-S batteries are presented.