Chen Weijie

An embedding 2D/3D heterostructure is in situ formed by incorporating a small amount of 4-guanidinobutanoic acid, which markedly suppresses nonradiative recombination, leading to high efficiencies of 21.45% and 20.16% for the rigid and flexible perovskite devices, respectively.

Abstract

Flexible perovskite solar cells (f-PSCs) have attracted increasing attention because of their enormous potential for use in consumer electronic devices. The key to achieve high device performance is to deposit pinhole-free, uniform and defect-less perovskite films on the rough surface of polymeric substrates. Here, a solvent engineering to tailor the crystal morphology of FA-alloyed perovskite films prepared by one-step blade coating is first deployed. It is found that the use of binary solvents DMF:NMP, rather than the conventional DMF:DMSO, enables to deposit dense and uniform FA-alloyed perovskite films on both the rigid and flexible substrates. As a decisive step, an embedding 2D/3D perovskite heterostructure is in situ formed by incorporating a small amount of 4-guanidinobutanoic acid (GBA). Accordingly, photovoltage increases up to 100 mV are realized due to the markedly suppressed nonradiative recombination, leading to high efficiencies of 21.45% and 20.16% on the rigid and flexible substrates, respectively. In parallel, improved mechanical robustness of the flexible devices is achieved due to the presence of the embedded 2D phases. The results underpin the importance of morphology control and defect passivation in delivering high-performance flexible FA-alloyed flexible perovskite devices.

Methylammonium chloride (MACl) or formamidine chloride (FACl) of perovskite precursor is added into SnO₂ electron transport layer (ETL) and reacts with PbI₂ to form perovskite crystal nucleus, which improves the contact between SnO₂ ETL and perovskite, as well as the morphology and crystallinity of perovskite layer, and greatly improves the fill factor (FF) of perovskite solar cells (PSCs).

Abstract

The electron transport layer (ETL) is a key component of regular perovskite solar cells to promote the overall charge extraction efficiency and tune the crystallinity of the perovskite layer for better device performance. The authors present a novel protocol of ETL engineering by incorporating a composition of the perovskite precursor, methylammonium chloride (MACl), or formamidine chloride (FACl), into SnO₂ layers, which are then converted into the crystal nuclei of perovskites by reaction with PbI₂. The SnO₂-embedded nuclei remarkably improve the morphology and crystallinity of the optically active perovskite layers. The improved ETL-to-perovskite electrical contact and dense packing of large-grained perovskites enhance the carrier mobility and suppress charge recombination. The power conversion efficiency increases from 20.12% (blank device) to 21.87% (21.72%) for devices with MACl (FACl) as an ETL dopant. Moreover, all the precursor-engineered cells exhibit a record-high fill factor (82%).

Herein, lead acetate and lead thiocyanate are explored as dual lead sources to prepare high-quality methylammonium lead iodide perovskite films in ambient air through an eco-friendly way, which results in unprecedented efficiency for perovskite solar cells prepared from non-halide lead sources. In addition, the device also shows excellent air stability.

Abstract

The realization of highly efficient perovskite solar cells (PSCs) in ambient air is considered to be advantageous for low-cost commercial manufacturing. However, it is fundamentally difficult to achieve comparable device performance to that obtained in an inert atmosphere, especially when the ambient humidity is high. Here, an effective precursor engineering that simultaneously employs non-halide lead acetate and lead thiocyanate lead sources for fabricating high-quality methylammonium lead iodide perovskite films in ambient air with enhanced moisture tolerance, is reported. The presence of Ac^– and SCN^– ions not only enables the facile formation of homogeneous and highly crystalized perovskite films, but also directs the uniform growth of the crystals along the (110) direction. Accordingly, a 20.55% efficiency is demonstrated, one of the best results for air-processed MAPbI₃ PSCs, which is also the highest value achieved with non-halide lead sources. Furthermore, the unencapsulated device shows fivefold prolonged air stability (3600 h) compared to the conventional PbI₂-based PSC. Together with the use of non-toxic antisolvent, this strategy is fully compatible with ambient air operation and thus of great potential for practical applications.

A facile one-step method to in situ deposit γ-phase 3D CsPbI₃ films consisting of cuboid crystallites is achieved by introducing 1,3-propanediamine dihydriodide (PDAI). The PDAI–perovskite light-emitting diode (PeLED) can reach a record efficiency of 15.03% for 3D CsPbI₃ PeLEDs and a peak efficiency of 10.30% of a 9 cm² PeLED.

Abstract

Inorganic CsPbI₃ perovskite with high chemical stability is attractive for efficient deep-red perovskite light-emitting diodes (PeLEDs) with high color purity. Compared to PeLEDs based on ex-situ-synthesized CsPbI₃ nanocrystals/quantum dots suffering from low conductivity and efficiency droop under high current densities, in situ deposited 3D CsPbI₃ films from precursor solutions can maintain high conductivity but show high trap density. Here, it is demonstrated that introducing diammonium iodide can increase the size of colloids in the precursor solution, retard the phase-transition rate, and passivate trap states of the in-situ-formed cuboid crystallites. The PeLED based on the one-step-formed 3D CsPbI₃ cuboid crystallite films shows a peak external quantum efficiency (EQE) value up to 15.03% because of the high conductivity and reduced trap states. Furthermore, this one-step method also has a wide processing window, which is attractive for flow-line production of large-area PeLED modules. The fabrication of a 9 cm² PeLED that exhibits a peak EQE of 10.30% is successfully demonstrated.

Recent developments of the quinoxaline-based D–A copolymers for the applications as polymer donor in polymer solar cells and as hole transport material in perovskite solar cells are reviewed.

Abstract

Polymer solar cells (PSCs) have achieved great progress recently, benefiting from the rapid development of narrow bandgap small molecule acceptors and wide bandgap conjugated polymer donors. Among the polymer donors, the D–A copolymers with quinoxaline (Qx) as A-unit have received increasing attention since the report of the low-cost and high-performance D–A copolymer donor based on thiophene D-unit and difluoro-quinoxalline A-unit in 2018. In addition, the weak electron-deficient characteristic and the multiple substitution positions of the Qx unit make it an ideal A-unit in constructing the wide bandgap polymer donors with different functional substitutions. In this review article, recent developments of the Qx-based D–A copolymer donors, including synthetic method of the Qx unit, backbone modulation, side chain optimization, and functional substitution of the Qx-based D–A copolymers, are summarized and discussed. Furthermore, the application of the Qx-based D–A copolymers as hole transport material in perovskite solar cells (pero-SCs) is also introduced. The focus mainly on the molecular design strategies and structure–properties relationship of the Qx-based D–A copolymers, aiming to provide a guideline for developing high-performance Qx-based D–A copolymers for the applications as donor in PSCs and as hole transport material in pero-SCs.

Publication date: December 2021

Source: Nano Energy, Volume 90, Part A

Author(s): Sawanta S. Mali, Jyoti V. Patil, Julian A. Steele, Chang Kook Hong

Publication date: December 2021

Source: Nano Energy, Volume 90, Part A

Author(s): Cong Chen, Jiwei Liang, Junjun Zhang, Xinxing Liu, Xinxing Yin, Hongsen Cui, Haibing Wang, Chen Wang, Zaifang Li, Junbo Gong, Qianqian Lin, Weijun Ke, Chen Tao, Bo Da, Zejun Ding, Xudong Xiao, Guojia Fang

Publication date: December 2021

Source: Nano Energy, Volume 90, Part B

Author(s): Yuhong Zhang, Lin Xu, Yanjie Wu, Qingqing Zhou, Zhichong Shi, Xinmeng Zhuang, Bin Liu, Biao Dong, Xue Bai, Wen Xu, Donglei Zhou, Hongwei Song

A thorough overview is given on the fundamental properties of tin halide perovskites tailored to their application in solar cells. A detailed discussion of the crystal structure, electronic properties, photophysics, and thin-film crystallization of tin halide perovskites provides a foundation to highlight its exceptional properties and reveals research strategies to improve the performance of tin halide solar cells.

Abstract

Metal halide perovskites have unique optical and electrical properties, which make them an excellent class of materials for a broad spectrum of optoelectronic applications. However, it is with photovoltaic devices that this class of materials has reached the apotheosis of popularity. High power conversion efficiencies are achieved with lead-based compounds, which are toxic to the environment. Tin-based perovskites are the most promising alternative because of their bandgap close to the optimal value for photovoltaic applications, the strong optical absorption, and good charge carrier mobilities. Nevertheless, the low defect tolerance, the fast crystallization, and the oxidative instability of tin halide perovskites currently limit their efficiency. The aim of this review is to give a detailed overview of the crystallographic, photophysical, and optoelectronic properties of tin-based perovskite compounds in their multiple forms from 3D to low-dimensional structures. At the end, recent progress in tin-based perovskite solar cells are reviewed, mainly focusing on the detail of the strategies adopted to improve the device performances. For each subtopic, the current challenges and the outlook are discussed, with the aim to stimulate the community to address the most important issues in a concerted manner.

Hierarchical morphology modifications in layer-by-layer organic solar cells are achieved by a multi-functional volatile solid additive, yielding favorable vertical component distribution and molecular packing. This work realizes simultaneous improvements in device efficiency and stability, providing a practical method for morphology control in layer-by-layer devices.

Abstract

Layer-by-layer (LBL) deposition strategy enabling favorable vertical phase distributions has been regarded as promising candidates for constructing high-efficient organic photovoltaic (OPV) cells. However, solid additives with the merits of good stability and reproducibility have been rarely used to fine-tune the morphology of the LBL films for improved efficiency and stability. Herein, hierarchical morphology control in LBL OPV is achieved via a dual functional solid additive. Series of LBL devices are fabricated by introducing the solid additive individually or simultaneously to the donor or acceptor layer to clarify the functions of additives. Additive in the donor layer can facilitate the formation of preferable vertical component distribution, and that in the acceptor layer will enhance the molecular crystallinity for better charge transport properties. The optimized morphology ultimately contributed to high PCEs of 16.4% and 17.4% in the binary and quaternary LBL devices. This reported method provides an alternative way to controllably manipulate the morphology of LBL OPV cells.

2D mixed halide perovskites with bandgap tunability and increased stability are employed in photovoltaics, light-emitting diodes, and optoelectronics. Inherent halide ion mobility (instability) of mixed halides drives photoinduced halide ion segregation. The important role of dimensionality across 3D to 2D perovskites governs the excited-state dynamics and the kinetics of halide segregation and dark recovery.

Abstract

2D lead halide perovskites, which exhibit bandgap tunability and increased chemical stability, have been found to be useful for designing optoelectronic devices. Reducing dimensionality with decreasing number of layers (n = 10–1) also imparts resistance to light-induced ion migration as seen from the halide ion segregation and dark recovery in mixed halide (Br:I = 50:50) perovskite films. The light-induced halide ion segregation efficiency, as determined from difference absorbance spectra, decreases from 20% to <1% as the dimensionality is decreased for 2D perovskite film from n = 10 to 1. The segregation rate constant (k _segregation), which decreases from 5.9 × 10⁻³ s⁻¹ (n = 10) to 3.6 × 10⁻⁴ s⁻¹ (n = 1), correlates well with nearly an order of magnitude decrease observed in charge-carrier lifetime (τ_average = 233 ps for n = 10 vs τ_avg = 27 ps for n = 1). The tightly bound excitons in 2D perovskites make charge separation less probable, which in turn decreases the halide mobility and resulting phase segregation. The importance of controlling the dimensionality of the 2D architecture in suppressing halide ion mobility is discussed.

Cost-effective carbazole donors toward efficient hole transport materials (HTMs) have been developed based on the arylamine-carbazole hybrid strategy. The perovskite solar cells based on M143 achieve a power conversion efficiency over 20%, which is among the highest performance for organic HTMs with carbazole donors.

The extraordinary electronic and structural properties of carbazole make it an important donor for the molecular design of hole transport materials (HTMs). However, the development of peripheral carbazole donors has lagged behind. Herein, a series of low-cost arylamine-substituted carbazole donors are synthesized by a one-step facile method. The effect of the terminal arylamine on the optoelectronic, thermal stability, hole mobility, and photovoltaic properties of the studied carbazole HTMs is also investigated. The diphenylamine- and carbazole-substituted carbazoles possess the orthogonal–planar conformation, endowing the HTMs (M142 and M143) with excellent electronic properties and morphological properties. Consequently, power conversion efficiencies (PCEs) of 19.60% and 20.05% accompanied with a high photovoltage are achieved for M142- and M143-based doped devices, respectively, outperforming the controlled cells based on nonsubstituted carbazole HTM (M145, PCE = 17.25%). Moreover, the devices based on M143 exhibit good long-term storage, thermal, and light stability. This work provides a simple strategy for molecular design in developing efficient carbazole donors.

Benefitting from the synergistic effect of anion and cation, additive engineering employing antimony acetate enables the fabrication of stable CH₃NH₃PbI₃-based perovskite solar cell with efficiency beyond 21%, in which the acetate ion plays an important role in optimizing the perovskite film morphology while the antimony ion is more involved in tailoring the electronic properties of perovskite.

Abstract

Both the film quality and the electronic properties of halide perovskites have significant influences on the photovoltaic performance of perovskite solar cells (PSCs) because both of them are closely related to the charge carrier transportation, separation, and recombination processes in PSCs. In this work, an additive engineering strategy using antimony acetate (Sb(Ac)₃) is employed to enhance the photovoltaic performance of methylammonium lead iodide (MAPbI₃)-based PSCs by improving the film quality and optimizing the photoelectronic properties of halide perovskites. It is found that Ac⁻ and Sb³⁺ of Sb(Ac)₃ play different roles and their synergistic effect contributed to the eventual excellent photovoltaic performance of MAPbI₃-based PSCs with a power conversion efficiency of above 21%. The Ac⁻ anions act as a crystal growth controller and are more involved in the improvement of perovskite film morphology. By comparison, Sb³⁺ cations are more involved in the optimization of the electronic structure of perovskites to tailor the energy levels of the perovskite film. Furthermore, with the assistance of Sb(Ac)₃, MAPbI₃-based PSCs deliver much improved moisture, air, and thermal stability. This work can provide scientific insights on the additive engineering for improving the efficiency and long-term stability of MAPbI₃-based PSCs, facilitating the further development of perovskite-based optoelectronics.

In this work, a series of fully degradable n-type conjugated polymers (PNDIT2/IM-f) are developed for high-performance and transient organic electronics.

Abstract

Degradable organic semiconductors have significant potential for transient and biomedical organic electronics, but there have been only a few studies on fully degradable conjugated polymers (CPs) that achieve high electrical performance. In addition, these examples are limited to p-type CPs. In this study, a series of fully degradable n-type CPs, naphthalene diimide (NDI)-based terpolymer (PNDIT2/IM-f) are developed. The incorporation of an imine linker (IM) into the CP backbone affords the capability of facile hydrolysis degradation while maintaining efficient π-conjugations and excellent electrical properties. An additional benefit of this molecular design is the systematic tunability of the degradation characteristics and electrical performance depending on the IM content (f _IM). At the optimal point (f _IM = 0.45) that enables complete degradation of the polymer under acidic conditions, the resulting PNDIT2/IM-0.45 film exhibits high electron mobility (μ_e) of 0.04 cm² V⁻¹ s⁻¹ in organic field-effect transistors (OFETs), demonstrating excellent potential as transient OFETs. The high μ_e value is mainly attributed to the enlarged edge-on orientations and tighter stacking of PNDIT2/IM-f crystallites as increasing f _IM. Thus, this study provides useful guidelines for the design of fully degradable n-type CPs and establishes an important correlation between the molecular structure−electronic performance−transient properties.

The interaction energies of solvents and co-solvents with perovskite precursors control the crystallization dynamics of mixed dimensional perovskites. Solvent engineering thus enables the manipulation of the phase distribution towards favorably oriented 2D phases with a narrow distribution of the number of inorganic layers in the 2D perovskite towards materials that provide solar cells with efficiency exceeding 11%.

Abstract

Solution-processed quasi-2D perovskites are promising for stable and efficient solar cells because of their superior environmental stability compared to 3D perovskites and tunable optoelectronic properties. Changing the number of inorganic layers (n) sandwiched between the organic spacers allows for tuning of the bandgap. However, narrowing the phase distribution around a specific n-value is a challenge. In-situ UV–vis–NIR absorption spectroscopy is used to time-resolve the crystallization dynamics of quasi-2D butylammonium-based (BA) perovskites with <n> = 4, processed from N,N-dimethylformamide (DMF) in the presence of different co-solvents. By combining with photoluminescence, transient absorption, and grazing-incidence wide-angle X-ray scattering, the crystallization is correlated to the distribution of phases with different n-values. Infrared spectroscopy and density functional theory reveal that the phase distribution correlates with perovskite precursor—co-solvent interaction energies and that stronger interactions shift the phase distribution towards smaller n-values. Careful tuning of the solvent/co-solvent ratio provides a more homogeneous phase distribution, with highly oriented perovskite crystals and suppressed formation of n = 1–2 phases, providing a power conversion efficiency for BA₂MA₃Pb₄I₁₃ solar cells that increases from 3.5% when processed from DMF to over 11% and 10% when processed from DMF/dimethyl sulfoxide and DMF/N-methyl-2-pyrrolidone mixtures, respectively.

A sponge-like Cu-doping SnO₂-NiO p-n semiconductor heterostructure (SnO₂-NiO_x/Cu), was created as a CM-based SERS substrate with a significant EF >10¹⁰. SnO₂-NiO_x/Cu was then developed as a SERS nose for selective recognition of multiple lung cancer related VOCs down to ppb level. The information of VOCs recorded in a barcode demonstrated practical potential of a desktop SERS device for biomarker screening.

Abstract

Surface enhanced Raman scattering (SERS) based on chemical mechanism (CM) attracts tremendous attention for great selectivity and stability. However, low enhancement factor (EF) limits its practical applications for trace detection. Here, a novel sponge-like Cu-doping SnO₂-NiO p-n semiconductor heterostructure (SnO₂-NiO_x/Cu), was first created as a CM-based SERS substrate with a significant EF of 1.46×10¹⁰. This remarkable EF was mainly attributed to the enhanced charge-separation efficacy of p-n heterojunction and charge transfer resonance resulted from Cu doping. Moreover, the porous structure enriched the probe molecules, resulting in further SERS signals magnification. By immobilizing CuPc as an inner-reference element, SnO₂-NiO_x/Cu was developed as a SERS nose for selective recognition of multiple lung cancer related VOCs down to ppb level. The information of VOCs was recorded in a barcode, demonstrating practical potential of a desktop SERS device for biomarker screening.