JIANG ZHI XUAN

Nature Chemistry, Published online: 20 July 2020; doi:10.1038/s41557-020-0521-5

CsPbI₃ perovskite quantum dot (PQD) hybrid nonfullerene organic solar cells are fabricated. The devices based on a PTB7‐Th:FOIC blend with PQDs yield higher efficiency of 13.2% even at near‐zero driving force than that without PQDs (11.6%). Incorporation of PQDs also leads to efficiency enhancement from 15.4% to 16.6% for a PM6:Y6 blend.

Abstract

To take advantages of the intense absorption and fluorescence, high charge mobility, and high dielectric constant of CsPbI₃ perovskite quantum dots (PQDs), PQD hybrid nonfullerene organic solar cells (OSCs) are fabricated. Addition of PQDs leads to simultaneous enhancement of open‐circuit voltage (V _OC), short‐circuit current density (J _SC), and fill factor (FF); power conversion efficiencies are boosted from 11.6% to 13.2% for PTB7‐Th:FOIC blend and from 15.4% to 16.6% for PM6:Y6 blend. Incorporation of PQDs dramatically increases the energy of the charge transfer state, resulting in near‐zero driving force and improved V _OC. Interestingly, at near‐zero driving force, the PQD hybrid OSCs show more efficient charge generation than the control device without PQDs, contributing to enhanced J _SC, due to the formation of cascade band structure and increased molecular ordering. The strong fluorescence of the PQDs enhances the external quantum efficiency of the electroluminescence of the active layer, which can reduce nonradiative recombination voltage loss. The high dielectric constant of the PQDs screens the Coulombic interactions and reduces charge recombination, which is beneficial for increased FF. This work may open up wide applicability of perovskite quantum dots and an avenue toward high‐performance nonfullerene solar cells.

Aiming at stable and efficient perovskite light‐emitting diodes (PeLEDs), this work proposes an all‐inorganic strategy involving an insulator–perovskite–insulator device structure and cascade ZnS‐ZnSe electron transport layers, which improve charge‐injection efficiency and suppress the electric‐field‐induced ion migration channels. The findings provide an addressable approach access to future commercialization of PeLEDs.

Abstract

Stability issue is one of the major concerns that limit emergent perovskite light‐emitting diodes (PeLEDs) techniques. Generally, ion migration is considered as the most important origin of PeLEDs degradation. In this work, an all‐inorganic device architecture, LiF/perovskite/LiF/ZnS/ZnSe, is proposed to address this imperative problem. The inorganic (Cs_{1− x} Rb _x )_{1− y} K _y PbBr₃ perovskite is optimized with achieving a photoluminescence quantum yield of 67%. Depth profile analysis of X‐ray photoelectron spectroscopy indicates that the LiF/perovskite/LiF structure and the ZnS/ZnSe cascade electron transport layers significantly suppress the electric‐field‐induced ion migrations of the perovskite layers, and impede the diffusion of metallic atoms from cathode into perovskites. The as‐prepared PeLEDs display excellent shelf stability (maintaining 90% of the initial external quantum efficiency [EQE] after 264 h) and operational stability (half‐lifetime of about 255 h at an initial luminance of 120 cd m⁻²). The devices also exhibit a maximum brightness of 15 6155 cd m⁻² and an EQE of 11.05%.

Nature Chemistry, Published online: 20 July 2020; doi:10.1038/s41557-020-0521-5

Herein, quasi‐heteroface perovskite solar cells (QHF‐PSCs) are reported. Compared with normal PSCs, QHF‐PSCs have better carrier separation capabilities and effectively suppress the nonradiative recombination. Meanwhile, middle band gap perovskite layer is obtained by combining a wide band gap perovskite layer with a narrow band gap perovskite layer. This strategy points out a new avenue to further expand the application of perovskite materials.

Abstract

Perovskite solar cells (PSCs) have attracted unprecedented attention due to their rapidly rising photoelectric conversion efficiency (PCE). In order to further improve the PCE of PSCs, new possible optimization path needs to be found. Here, quasi‐heteroface PSCs (QHF‐PSCs) is designed by a double‐layer perovskite film. Such brand new PSCs have good carrier separation capabilities, effectively suppress the nonradiative recombination of the PSCs, and thus greatly improve the open‐circuit voltage and PCE. The root cause of the performance improvement is the benefit from the additional built‐in electric field, which is confirmed by measuring the external quantum efficiency under applied electric field and Kelvin probe force microscope. Meanwhile, an intermediate band gap perovskite layer can be obtained simply by combining a wide band gap perovskite layer with a narrow band gap perovskite layer. Tunability of the band gap is obtained by varying the film thicknesses of the narrow and wide band gap layers. This phenomenon is quite different from traditional inorganic solar cells, whose band gap is determined only by the narrowest band gap layer. It is believed that these QHF‐PSCs will be an effective strategy to further enhance PCE in PSCs and provide basis to further understand and develop the perovskite materials platform.

Herein, quasi‐heteroface perovskite solar cells (QHF‐PSCs) are reported. Compared with normal PSCs, QHF‐PSCs have better carrier separation capabilities and effectively suppress the nonradiative recombination. Meanwhile, middle band gap perovskite layer is obtained by combining a wide band gap perovskite layer with a narrow band gap perovskite layer. This strategy points out a new avenue to further expand the application of perovskite materials.

Abstract

Perovskite solar cells (PSCs) have attracted unprecedented attention due to their rapidly rising photoelectric conversion efficiency (PCE). In order to further improve the PCE of PSCs, new possible optimization path needs to be found. Here, quasi‐heteroface PSCs (QHF‐PSCs) is designed by a double‐layer perovskite film. Such brand new PSCs have good carrier separation capabilities, effectively suppress the nonradiative recombination of the PSCs, and thus greatly improve the open‐circuit voltage and PCE. The root cause of the performance improvement is the benefit from the additional built‐in electric field, which is confirmed by measuring the external quantum efficiency under applied electric field and Kelvin probe force microscope. Meanwhile, an intermediate band gap perovskite layer can be obtained simply by combining a wide band gap perovskite layer with a narrow band gap perovskite layer. Tunability of the band gap is obtained by varying the film thicknesses of the narrow and wide band gap layers. This phenomenon is quite different from traditional inorganic solar cells, whose band gap is determined only by the narrowest band gap layer. It is believed that these QHF‐PSCs will be an effective strategy to further enhance PCE in PSCs and provide basis to further understand and develop the perovskite materials platform.

Herein the morphology and exciton/charge carrier dynamics in bulk heterojunctions of the donor polymer PTQ10 and molecular acceptor IDIC are investigated. The results emphasize the potential for high material crystallinity to enhance charge separation and collection in organic solar cells, but also that long exciton diffusion lengths are likely to be essential for efficient exciton separation in such high crystallinity devices.

Abstract

Herein the morphology and exciton/charge carrier dynamics in bulk heterojunctions (BHJs) of the donor polymer PTQ10 and molecular acceptor IDIC are investigated. PTQ10:IDIC BHJs are shown to be particularly promising for low cost organic solar cells (OSCs). It is found that both PTQ10 and IDIC show remarkably high crystallinity in optimized BHJs, with GIWAXS data indicating pi‐pi stacking coherence lengths of up to 8 nm. Exciton‐exciton annihilation studies indicate long exciton diffusion lengths for both neat materials (19 nm for PTQ10 and 9.5 nm for IDIC), enabling efficient exciton separation with half lives of 1 and 3 ps, despite the high degree of phase segregation in this blend. Transient absorption data indicate exciton separation leads to the formation of two spectrally distinct species, assigned to interfacial charge transfer (CT) states and separated charges. CT state decay is correlated with the appearance of additional separate charges, indicating relatively efficient CT state dissociation, attributed to the high crystallinity of this blend. The results emphasize the potential for high material crystallinity to enhance charge separation and collection in OSCs, but also that long exciton diffusion lengths are likely to be essential for efficient exciton separation in such high crystallinity devices.

Solar cells based on 300 nm thick MAPbI₃ perovskite monocrystal are prepared, which show 3% enhancement in power conversion efficiency (PCE) compared to their polycrystalline counterparts. The suppressed charge recombination loss due to the reduction of grains and grain boundaries is believed to be the main reason for the PCE improvement.

Abstract

Grains and grain boundaries play key roles in determining halide perovskite‐based optoelectronic device performance. Halide perovskite monocrystalline solids with large grains, smaller grain boundaries, and uniform surface morphology improve charge transfer and collection, suppress recombination loss, and thus are highly favorable for developing efficient solar cells. To date, strategies of synthesizing high‐quality thin monocrystals (TMCs) for solar cell applications are still limited. Here, by combining the antisolvent vapor‐assisted crystallization and space‐confinement strategies, high‐quality millimeter sized TMCs of methylammonium lead iodide (MAPbI₃) perovskites with controlled thickness from tens of nanometers to several micrometers have been fabricated. The solar cells based on these MAPbI₃ TMCs show power conversion efficiency (PCE) of 20.1% which is significantly improved compared to their polycrystalline counterparts (PCE) of 17.3%. The MAPbI₃ TMCs show large grain size, uniform surface morphology, high hole mobility (up to 142 cm² V⁻¹ s⁻¹), as well as low trap (defect) densities. These properties suggest that TMCs can effectively suppress the radiative and nonradiative recombination loss, thus provide a promising way for maximizing the efficiency of perovskite solar cells.

An “S‐shaped, hook‐like” naphthalene diimide derivate, NDI‐BN, is adopted as a cathode interface layer in inverted perovskite solar cells and good power conversion efficiency of 21.32% with enhanced stability is achieved. The relationship between the molecular packing motif of the organic interface layer and the interfacial degradation mechanism is explored.

Abstract

Ion migration induced interfacial degradation is a detrimental factor for the stability of perovskite solar cells (PSCs) and hence requires special attention to address this issue for the development of efficient PSCs with improved stability. Here, an “S‐shaped, hook‐like” organic small molecule, naphthalene diimide derivative (NDI‐BN), is employed as a cathode interface layer (CIL) to tailor the [6,6]‐phenylC61‐butyric acid methylester (PCBM)/Ag interface in inverted PSCs. By realizing enhanced electron extraction capability via the incorporation of NDI‐BN, a peak power conversion efficiency of 21.32% is achieved. Capacitance–voltage measurements and X‐ray photoelectron spectroscopy analysis confirmed an obvious role of this new organic CIL in successfully blocking ionic diffusion pathways toward the Ag cathode, thereby preventing interfacial degradation and improving device stability. The molecular packing motif of NDI‐BN further unveils its densely packed structure with π–π stacking force which has the ability to effectually hinder ion migration. Furthermore, theoretical calculations reveal that intercalation of decomposed perovskite species into the NDI clusters is considerably more difficult compared with the PCBM counterparts. This substantial contrast between NDI‐BN and PCBM molecules in terms of their structures and packing fashion determines the different tendencies of ion migration and unveils the superior potential of NDI‐BN in curtailing interfacial degradation.

Tandem solar cells hold promise for breaking the second law of thermodynamics and Shockley–Queisser limits. So far, such devices have to be made via costly methods. The advent of perovskite‐based absorbers enables the fabrication of various tandem devices through low‐cost techniques by combination with different subcells.

Abstract

Tandem solar cells (TSCs) comprising stacked narrow‐bandgap and wide‐bandgap subcells are regarded as the most promising approach to break the Shockley–Queisser limit of single‐junction solar cells. As the game‐changer in the photovoltaic community, organic–inorganic hybrid perovskites became the front‐runner candidate for mating with other efficient photovoltaic technologies in the tandem configuration for higher power conversion efficiency, by virtue of their tunable and complementary bandgaps, excellent photoelectric properties, and solution processability. In this review, a perspective that critically dilates the progress of perovskite material selection and device design for perovskite‐based TSCs, including perovskite/silicon, perovskite/copper indium gallium selenide, perovskite/perovskite, perovskite/CdTe, and perovskite/GaAs are presented. Besides, all‐inorganic perovskite CsPbI₃ with high thermal stability is proposed as the top subcell in TSCs due to its suitable bandgap of ≈1.73 eV and rapidly increasing efficiency. To minimize the optical and electrical losses for high‐efficiency TSCs, the optimization of transparent electrodes, recombination layers, and the current‐matching principles are highlighted. Through big data analysis, wide‐bandgap perovskite solar cells with high open‐circuit voltage (V _oc) are in dire need in further study. In the end, opportunities and challenges to realize the commercialization of TSCs, including long‐term stability, area upscaling, and mitigation of toxicity, are also envisioned.

Layered hybrid perovskites based on (PDMA)FA _{n –1}Pb _n I_{3 n +1} (n = 1–3; PDMA = 1,4‐phenylenedimethanammonium) compositions are investigated by using combination of techniques, including X‐ray scattering measurements, molecular dynamics simulations, and density functional theory calculations, along with time‐resolved microwave conductivity measurements, to unravel unique structural and photophysical properties relevant to optoelectronic applications.

Abstract

Layered hybrid perovskites have emerged as a promising alternative to stabilizing hybrid organic–inorganic perovskite materials, which are predominantly based on Ruddlesden‐Popper structures. Formamidinium (FA)‐based Dion‐Jacobson perovskite analogs are developed that feature bifunctional organic spacers separating the hybrid perovskite slabs by introducing 1,4‐phenylenedimethanammonium (PDMA) organic moieties. While these materials demonstrate competitive performances as compared to other FA‐based low‐dimensional perovskite solar cells, the underlying mechanisms for this behavior remain elusive. Here, the structural complexity and optoelectronic properties of materials featuring (PDMA)FA _{n –1}Pb _n I_{3 n +1} (n = 1–3) formulations are unraveled using a combination of techniques, including X‐ray scattering measurements in conjunction with molecular dynamics simulations and density functional theory calculations. While theoretical calculations suggest that layered Dion‐Jacobson perovskite structures are more prominent with the increasing number of inorganic layers (n), this is accompanied with an increase in formation energies that render n > 2 compositions difficult to obtain, in accordance with the experimental evidence. Moreover, the underlying intermolecular interactions and their templating effects on the Dion‐Jacobson structure are elucidated, defining the optoelectronic properties. Consequently, despite the challenge to obtain phase‐pure n > 1 compositions, time‐resolved microwave conductivity measurements reveal high photoconductivities and long charge carrier lifetimes. This comprehensive analysis thereby reveals critical features for advancing layered hybrid perovskite optoelectronics.

In article number https://doi.org/10.1002/aenm.2020008232000823, Carr Hoi Yi Ho, Franky So and co‐workers presented a simple yet highly compatible interconnecting layer for organic tandem solar cells. All double‐junction tandem devices with different active layers show high reproducibility and efficiencies in several laboratories. Among these tandem devices, an excellent power conversion efficieny of 16.1% is achieved. In addition, most of the tandem devices achieve more than 40% enhancement from the single‐junction solar cell.

Solid‐state ¹⁹F magic angle spinning nuclear magnetic microscopy and elemental mapping are introduced to probe the structures of ternary and quaternary blends. The presence of the individual guest paths minimizes the influence on charge generation and transport of the host system, allowing cooperation of the parallel‐like subcells, producing impressive 17.2% efficiency via a quaternary strategy.

Abstract

Ternary strategies show over 16% efficiencies with increased current/voltage owing to complementary absorption/aligned energy level contributions. However, poor understanding of how the guest components tune the active layer structures still makes rational selection of material systems challenging. In this study, two phthalimide based ultrawide bandgap polymer donor guests are synthesized. Parallel energies between the highest occupied molecular orbitals of host and guest polymers are achieved via incorporating selnophene on the guest polymer. Solid‐state ¹⁹F magic angle spinning nuclear magnetic spectroscopy, graze‐incidence wide‐angle X‐ray diffraction, elemental transmission electron microscopy mapping, and transient absorption spectroscopy are combined to characterize the active layer structures. Formation of the individual guest phases selectively improves the structural order of donor and acceptor phase. The increased electron mobility in combination with the presence of the additional paths made by the guest not only minimizes the influence on charge generation and transport of the host system but also contributes to increasing the overall current generation. Therefore, phthalimide based polymers can be potential candidates that enable the simultaneous increase of open‐circuit voltage and short‐circuit current‐density via fine‐tuning energy levels and the formation of additional paths for enhancing current generation in parallel‐like multicomponent organic solar cells.

The emergence of nonfullerene electron acceptors has rejuvenated the field of organic photovoltaics, with device efficiencies over 18% and 20% in sight. In this essay, the basic properties of these new nonfullerene acceptors are discussed. Perspectives and suggestions for further research endeavors toward successful commercialization are also provided.

Abstract

Efficient, low‐cost, and low‐embodied energy photovoltaics are key enablers of the global decarbonization agenda. In addition to the market‐leading crystalline silicon technology, several other promising candidates are under active investigation with the perovskites leading the way with single‐junction efficiencies exceeding 25% at the lab‐scale. So‐called organic photovoltaics (solar cells based upon organic semiconductors), particularly those that can be solution processed, have long promised the Nirvana of ultralow cost and very short energy payback times. However, relatively low efficiencies, poor long‐term stability, and issues with manufacturing at scale have so far prevented truly meaningful commercialization of the technology. The recent emergence of the so‐called nonfullerene electron acceptors is potentially about to shift this dynamic—they have delivered a step change in performance in a relatively short period of time. In this Essay, the basic properties of these new materials, their pros and cons, what we know and what we do not know are explored.

Borophene is considered as one of the most promising 2D nanomaterials, owing to its unique structural and electronic properties. The various synthetic approaches for the fabrication of borophene nanostructures with different phases and morphologies, including free‐standing borophene sheets, are described. The frontline applications of these nanostructures in flexible electronics, sensing, disease diagnosis, catalysis, and hybrid energy storage are also considered.

Abstract

Borophene, a 2D allotrope of boron and the lightest elemental Dirac material, is the latest very promising 2D material owing to its unique structural and electronic characteristics of the X₃ and β₁₂ phases. The high atomic density on ridgelines of the β₁₂ phase of borophene provides a substantial orbital overlap, which leads to an excellent electron density in the conduction level and thus to a highly metallic behavior. These unique structural characteristics and electronic properties of borophene attract significant scientific interest. Herein, approaches for crystal growth/synthesis of these unique nanostructures and their potential technological applications are discussed. Various substrate‐supported ultrahigh‐vacuum growth techniques for borophene, such as molecular beam epitaxy, atomic layer deposition, and chemical vapor deposition, along with their challenges, are also summarized. The sonochemical exfoliation and modified Hummer's technique for the synthesis of free‐standing borophene are also discussed. Solution‐phase exfoliation seems to address the scalability issues and expands the applications of these unique materials to various fields, including renewable energy devices and ultrafast sensors. Furthermore, the electronic, optical, thermal, and elastic properties of borophene are thoroughly discussed and are compared with those of graphene and its “cousins.” Numerous frontline applications are envisaged and an outlook is presented.

The technology of pulsed laser irradiation in liquid from a solid target to liquid is pioneered, yielding liquid ternary supranano‐(<10 nm) alloys with a unique core–shell structure. The decoration of such supranano‐alloys as an electron mediator at grain boundaries promotes the electron extraction and transfer of the hybrid perovskite film of a perovskite solar cell and drives the efficiency up to 22.03%.

Abstract

Creating colloids of liquid metal with tailored dimensions has been of technical significance in nano‐electronics while a challenge remains for generating supranano (<10 nm) liquid metal to unravel the mystery of their unconventional functionalities. Present study pioneers the technology of pulsed laser irradiation in liquid from a solid target to liquid, and yields liquid ternary nano‐alloys that are laborious to obtain via wet‐chemistry synthesis. Herein, the significant role of the supranano liquid metal on mediating the electrons at the grain boundaries of perovskite films, which are of significance to influence the carriers recombination and hysteresis in perovskite solar cells, is revealed. Such embedding of supranano liquid metal in perovskite films leads to a cesium‐based ternary perovskite solar cell with stabilized power output of 21.32% at maximum power point tracing. This study can pave a new way of synthesizing multinary supranano alloys for advanced optoelectronic applications.

Judicious incorporation of ambiopolar black phosphorene with tailored thickness to concurrently impart electron and hole extractions in perovskite solar cells is reported by Jinsong Huang, Zhiqun Lin, and co‐workers in article number https://doi.org/10.1002/adma.2020009992000999. This work underpins the potential implementation of black phosphorene as a dual‐functional transport material for a diversity of optoelectronic devices, including photodetectors, sensors, and light‐emitting diodes.

The salt of the cation (Mes₂B⁺; Mes: mesitylene) and the anion [B(C₆F₅)₄]⁻ is introduced as superior p‐type dopant for organic semiconductors. The doping mechanism involves electron transfer from the semiconductor to Mes₂B⁺, and the positive charge is stabilized by [B(C₆F₅)₄]⁻. For poly(3‐hexylthiophene), the anion even stabilizes bipolarons. The effective electron affinity of Mes₂B⁺[B(C₆F₅)₄]⁻ is estimated to be 5.9 eV.

Abstract

Molecular doping allows enhancement and precise control of electrical properties of organic semiconductors, and is thus of central technological relevance for organic (opto‐) electronics. Beyond single‐component molecular electron acceptors and donors, organic salts have recently emerged as a promising class of dopants. However, the pertinent fundamental understanding of doping mechanisms and doping capabilities is limited. Here, the unique capabilities of the salt consisting of a borinium cation (Mes₂B⁺; Mes: mesitylene) and the tetrakis(penta‐fluorophenyl)borate anion [B(C₆F₅)₄]⁻ is demonstrated as p‐type dopant for polymer semiconductors. With a range of experimental methods, the doping mechanism is identified to comprise electron transfer from the polymer to Mes₂B⁺, and the positive charge on the polymer is stabilized by [B(C₆F₅)₄]⁻. Notably, the former salt cation leaves during processing and is not present in films. The anion [B(C₆F₅)₄]⁻ even enables the stabilization of polarons and bipolarons in poly(3‐hexylthiophene), not yet achieved with other molecular dopants. From doping studies with high ionization energy polymer semiconductors, the effective electron affinity of Mes₂B⁺[B(C₆F₅)₄]⁻ is estimated to be an impressive 5.9 eV. This significantly extends the parameter space for doping of polymer semiconductors.

Publication date: 15 January 2020

Source: Joule, Volume 4, Issue 1

Author(s): Jiahuan Zhang, Zaiwei Wang, Aditya Mishra, Maolin Yu, Mona Shasti, Wolfgang Tress, Dominik Józef Kubicki, Claudia Esther Avalos, Haizhou Lu, Yuhang Liu, Brian Irving Carlsen, Anand Agarwalla, Zishuai Wang, Wanchun Xiang, Lyndon Emsley, Zhuhua Zhang, Michael Grätzel, Wanlin Guo, Anders Hagfeldt

The salt of the cation (Mes₂B⁺; Mes: mesitylene) and the anion [B(C₆F₅)₄]⁻ is introduced as superior p‐type dopant for organic semiconductors. The doping mechanism involves electron transfer from the semiconductor to Mes₂B⁺, and the positive charge is stabilized by [B(C₆F₅)₄]⁻. For poly(3‐hexylthiophene), the anion even stabilizes bipolarons. The effective electron affinity of Mes₂B⁺[B(C₆F₅)₄]⁻ is estimated to be 5.9 eV.

Abstract

Molecular doping allows enhancement and precise control of electrical properties of organic semiconductors, and is thus of central technological relevance for organic (opto‐) electronics. Beyond single‐component molecular electron acceptors and donors, organic salts have recently emerged as a promising class of dopants. However, the pertinent fundamental understanding of doping mechanisms and doping capabilities is limited. Here, the unique capabilities of the salt consisting of a borinium cation (Mes₂B⁺; Mes: mesitylene) and the tetrakis(penta‐fluorophenyl)borate anion [B(C₆F₅)₄]⁻ is demonstrated as p‐type dopant for polymer semiconductors. With a range of experimental methods, the doping mechanism is identified to comprise electron transfer from the polymer to Mes₂B⁺, and the positive charge on the polymer is stabilized by [B(C₆F₅)₄]⁻. Notably, the former salt cation leaves during processing and is not present in films. The anion [B(C₆F₅)₄]⁻ even enables the stabilization of polarons and bipolarons in poly(3‐hexylthiophene), not yet achieved with other molecular dopants. From doping studies with high ionization energy polymer semiconductors, the effective electron affinity of Mes₂B⁺[B(C₆F₅)₄]⁻ is estimated to be an impressive 5.9 eV. This significantly extends the parameter space for doping of polymer semiconductors.