JIALINGBO

Fullerene Intercalation

In article number 1900508, Tobias Unruh and co‐workers report on the formation process of a PC60BM:pBTTT‐C14 active layer of a bulk heterojunction organic photovoltaic solar cell during evaporation of the solvent:additive mixture. By careful evaluation of the in‐situ grazing incidence small‐angle X‐ray scattering measurements, a conclusive picture of the 5‐step mechanism of fullerene intercalation and additive‐tuned evolution of the nanoscopic film structure during the drying process could be obtained.

Recent advances in covalent functionalization of single‐walled carbon nanotubes are explored to create intrinsically near‐infrared fluorescent carbon nanotube nanosensors with multimodal applications. Simultaneous covalent and noncovalent functionalizations on single‐walled carbon nanotube (SWCNT) surfaces interact through steric hindrance and intermolecular interactions. The ability to dual functionalize SWCNT nanoparticles has potential applications in diverse biotechnology applications including biomolecule imaging applications described herein.

Abstract

Optical nanoscale technologies often implement covalent or noncovalent strategies for the modification of nanoparticles, whereby both functionalizations are leveraged for multimodal applications but can affect the intrinsic fluorescence of nanoparticles. Specifically, single‐walled carbon nanotubes (SWCNTs) can enable real‐time imaging and cellular delivery; however, the introduction of covalent SWCNT sidewall functionalizations often attenuates SWCNT fluorescence. Recent advances in SWCNT covalent functionalization chemistries preserve the SWCNT's pristine graphitic lattice and intrinsic fluorescence, and here, such covalently functionalized SWCNTs maintain intrinsic fluorescence‐based molecular recognition of neurotransmitter and protein analytes. The covalently modified SWCNT nanosensor preserves its fluorescence response towards its analyte for certain nanosensors, presumably dependent on the intermolecular interactions between SWCNTs or the steric hindrance introduced by the covalent functionalization that hinders noncovalent interactions with the SWCNT surface. These SWCNT nanosensors are further functionalized via their covalent handles with a targeting ligand, biotin, to self‐assemble on passivated microscopy slides, and these dual‐functionalized SWCNT materials are explored for future use in multiplexed sensing and imaging applications.

A generic guideline for accurately controlling phase purity and arrangement in 2D perovskite films is provided by utilizing coordination engineering of a single‐crystal precursor solution. The resulting films with narrow distribution and preferentially perpendicular crystal orientation result in a significant improvement in device performance and stability, which is not typically found in conventional stoichiometric precursors.

Abstract

2D Ruddlesden–Popper perovskites (RPPs) have recently drawn significant attention because of their structural variability that can be used to tailor optoelectronic properties and improve the stability of derived photovoltaic devices. However, charge separation and transport in 2D perovskite solar cells (PSCs) suffer from quantum well barriers formed during the processing of perovskites. It is extremely difficult to manage phase distributions in 2D perovskites made from the stoichiometric mixtures of precursor solutions. Herein, a generally applicable guideline is demonstrated for precisely controlling phase purity and arrangement in RPP films. By visually presenting the critical colloidal formation of the single‐crystal precursor solution, coordination engineering is conducted with a rationally selected cosolvent to tune the colloidal properties. In nonpolar cosolvent media, the derived colloidal template enables RPP crystals to preferentially grow along the vertically ordered alignment with a narrow phase variation around a target value, resulting in efficient charge transport and extraction. As a result, a record‐high power conversion efficiency (PCE) of 14.68% is demonstrated for a (TEA)₂(MA)₂Pb₃I₁₀ (n = 3) photovoltaic device with negligible hysteresis. Remarkably, superior stability is achieved with 93% retainment of the initial efficiency after 500 h of unencapsulated operation in ambient air conditions.

The electron‐transport‐layer (ETL) free perovskite solar cells (PSCs) are attractive because of fewer layers and hence lower cost, but the lower photovoltaic performance, as compared to the ETL‐contained PSCs, largely restricts their practical applications. Herein, we design and synthesize hydroxylethyl functionalized imidazolium iodide, whose single crystal structure is determined, and propose self‐assembled ionic liquid on the conductive substrate for ETL‐free PSCs. It is found that the self‐assembly of the ionic liquid on the conductive substrate can lower the work function of the conductive substrate, enhance the interfacial electron extraction, and meanwhile retard the interfacial charge recombination. As a consequence, the power conversion efficiency is improved remarkably from 9.01% to 17.31% upon the self‐assembly of ionic liquid on the conductive substrate. This finding provides a new way to achieve highly efficient ETL free PSCs.

A polymerization‐assisted grain growth strategy in the sequential deposition method of perovskite thin films is demonstrated by triggering a polymerization process during PbI₂ film annealing. This strategy effectively passivates undercoordinated lead ions, reduces defect density, and boosts power conversion efficiency up to 23.0%, together with a prolonged lifetime.

Abstract

Intrinsically, detrimental defects accumulating at the surface and grain boundaries limit both the performance and stability of perovskite solar cells. Small molecules and bulkier polymers with functional groups are utilized to passivate these ionic defects but usually suffer from volatility and precipitation issues, respectively. Here, starting from the addition of small monomers in the PbI₂ precursor, a polymerization‐assisted grain growth strategy is introduced in the sequential deposition method. With a polymerization process triggered during the PbI₂ film annealing, the bulkier polymers formed will be adhered to the grain boundaries, retaining the previously established interactions with PbI₂. After perovskite formation, the polymers anchored on the boundaries can effectively passivate undercoordinated lead ions and reduce the defect density. As a result, a champion power conversion efficiency (PCE) of 23.0% is obtained, together with a prolonged lifetime where 85.7% and 91.8% of the initial PCE remain after 504 h continuous illumination and 2208 h shelf storage, respectively.

Charge selective contact between perovskite absorber and charge transport layer is modified via air‐stable n‐doping fullerene, producing multiple beneficial effects, and thus improving both efficiency and stability of perovskite solar cells.

Abstract

As one common electron transport material for planar n‐i‐p perovskite solar cell, titanium dioxide (TiO₂) compact layer has several challenging issues, such as surface hydroxyl groups, high defect density, and unmatched energy levels, causing severe energy loss and poor stability at contact. To solve these problems, the authors introduce a thin [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) interlayer doped with an air stable n‐type dopant, 3‐dimethyl‐2‐phenyl‐2,3‐dihydro‐1H‐benzoimidazole (DMBI) to modify the TiO₂ surface. The state‐of‐the‐art characterizations demonstrate such modification significantly improves charge transfer at MAPbI₃/TiO₂ interface together with smaller energy level offset, leading to suppressed charge recombination. High‐quality perovskite film with larger crystal grain size grows on the n‐doped PCBM/TiO₂ attributed to the better surface affinity. As a result, the average power conversion efficiency of perovskite solar cell exhibits a prominent improvement from 17.46% to 20.14%, with an enhancement in all device photovoltaic parameters. In addition, the stability of the device with n‐doped PCBM/TiO₂ is much better than that of the control device with the bare TiO₂ due to hydrophobicity nature of PCBM and low defect densities in the perovskite film and at the interface. This work indicates that many further device performance improvements should be conceivable by focusing on the perovskite interface.

A strong fluorine‐containing Lewis acid tris(pentafluorophenyl) phosphine (TPFP) is developed to passivate mixed perovskite solar cells, achieving a champion efficiency of 22.02% and a high stability under 85% relative humidity. The moisture degradation mechanism is phase segregation of I‐rich black phase and Cs/Br‐rich yellow phase resulting from water‐assisted synergistic Cs and halide ion migrations.

Abstract

Multiple‐cation lead mixed‐halide perovskites (MLMPs) have been recognized as ideal candidates in perovskite solar cells in terms of high efficiency and stability due to decreased open‐circuit voltage loss and suppressed yellow phase formation. However, they still suffer from an unsatisfactory long‐term moisture stability. In this study, phosphorus‐containing Lewis acid and base molecules are employed to improve device efficiency and stability based on their multifunction including recombination reduction, phase segregation suppression, and moisture resistance. The strong fluorine‐containing Lewis acid treatment can achieve a champion PCE of 22.02%. Unencapsulated and encapsulated devices retain 63% and 80% of the initial efficiency after 14 days of aging under 75% and 85% relative humidity, respectively. The better passivation of Lewis acid implies more halide defects than Pb defects at the MLMP surface. This unbalanced defect type results from phase segregation that is the synergistic effect of Cs and halide ion migrations. Identifying defect type based on different passivation effects is beneficial to not only choose suitable passivators to boost the efficiency and slow down the moisture degradation of MLMP solar cells, but also to understand the mechanism of defect‐assisted moisture degradation.

Nature Communications, Published online: 04 March 2020; doi:10.1038/s41467-020-15016-2

Nature Communications, Published online: 04 March 2020; doi:10.1038/s41467-020-15037-x

Highly efficient all‐inorganic perovskite solar cells based on CsPbI _x Br_{3‐ x} are fabricated through the introduction of a spontaneous interfacial manipulation method. A spontaneously formed ultrathin 2D perovskite top interface can not only eliminate interfacial defects but also effectively prevent moisture penetration. As a result, the device exhibits a power conversion efficiency of 18% with extended device stability.

Abstract

Cesium‐based all‐inorganic halide perovskites solar cells (PSCs) have recently attracted increasing attention. Currently, due to the existence of high defects density and unoptimized interfacial morphology, “state‐of‐the‐art” performances of all‐inorganic PSCs are still far away from their theoretical limits. Although commonly used two‐step passivation methods can effectively passivate the perovskite surface, they will inevitably detriment the original perovskite morphology due to the use of weak‐polarity solvents. This will potentially result in the unintentional doping, uncontrollable interfacial band alignment, and the additional defects formation. Hence, a spontaneous interfacial manipulation (SIM) method is developed to self‐organize a 2D/3D multidimensional perovskite top interface. It is demonstrated that the spontaneously formed ultrathin 2D perovskite can not only eliminate the interfacial defects, but also effectively prevent moisture penetration. As a result, a significant power conversion efficiency enhancement from 13.64% to over 18% is obtained along with greatly extended device lifetime, for CsPbI _x Br_{3‐ x} ‐based all‐inorganic PSC.

In article number https://doi.org/10.1002/admi.2019017161901716, Hongwei Lei, Song Zhang, Zuojun Tan, and co‐workers report a novel and efficient perovskite defect passivation strategy using silica oligomer. TEOS‐processed silica oligomer is in situ introduced into perovskite films to serve as a passivation agent (PA) for perovskite solar cells (PVSCs). Silica oligomer PA can enlarge perovskite grain sizes, prolong carrier lifetime, enhance charge carrier dynamics and reduce trap state densities, resulting in highly efficient PVSCs with good humid and thermal stability.

A novel bifunctional (anti)solvent system is developed for regulating the perovskite crystallization procedure. It can perform not only as an antisolvent at the spin‐coating step to rapidly generate crystal seeds, but also as a solvent for ripening the precursors to large crystal grains during the thermal‐annealing process. Therefore, it can significantly enhance the efficiency, stability, and reproducibility of perovskite solar cells.

Abstract

The preparation of high‐quality perovskite films is important for achieving high‐performance perovskite solar cells (PSCs). The effective balance between solvent and antisolvent is an essential factor for regulating high‐quality perovskite film during the spin‐coating and thermal‐annealing steps. In this work, a greener, nonhalogenated, nontoxic bifunctional (anti)solvent, methyl benzoate (MB), is developed not only as an antisolvent to rapidly generate crystal seeds at the perovskite spin‐coating step, but also as a digestive‐ripening solvent for the perovskite precursors, which can prevent the loss of organic components during the thermal‐annealing stage and effectively suppress the formation of miscellaneous lead halide phases. As a result, this novel bifunctional (anti)solvent is employed in planar n–i–p PSCs for engineering high‐quality perovskite layers and thus achieving a power conversion efficiency up to 22.37% with negligible hysteresis and >1300 h stability. Moreover, due to the high boiling point and low‐volatility characteristic of MB, high‐performance PSCs are achieved reproducibly at different operating temperatures (22–34 °C). Therefore, this developed bifunctional solvent system can provide a promising platform toward globally upscaling and commercializing PSCs in all seasons and regions.

GABr doping in ideal‐bandgap (≈1.34 eV) Sn–Pb binary perovskite films can efficiently reduce the defect density caused by Sn²⁺ oxidation in the perovskite and reduce the V _OC deficit. As a result, the best PCE of 20.63% with a record small V _OC deficit of 0.33 V is achieved in Sn–Pb binary 1.35 eV PSCs.

Abstract

1.5–1.6 eV bandgap Pb‐based perovskite solar cells (PSCs) with 30–31% theoretical efficiency limit by the Shockley–Queisser model achieve 21–24% power conversion efficiencies (PCEs). However, the best PCEs of reported ideal‐bandgap (1.3–1.4 eV) Sn–Pb PSCs with a higher 33% theoretical efficiency limit are <18%, mainly because of their large open‐circuit voltage (V _oc) deficits (>0.4 V). Herein, it is found that the addition of guanidinium bromide (GABr) can significantly improve the structural and photoelectric characteristics of ideal‐bandgap (≈1.34 eV) Sn–Pb perovskite films. GABr introduced in the perovskite films can efficiently reduce the high defect density caused by Sn²⁺ oxidation in the perovskite, which is favorable for facilitating hole transport, decreasing charge‐carrier recombination, and reducing the V _oc deficit. Therefore, the best PCE of 20.63% with a certificated efficiency of 19.8% is achieved in 1.35 eV PSCs, along with a record small V _oc deficit of 0.33 V, which is the highest PCE among all values reported to date for ideal‐bandgap Sn–Pb PSCs. Moreover, the GABr‐modified PSCs exhibit significantly improved environmental and thermal stability. This work represents a noteworthy step toward the fabrication of efficient and stable ideal‐bandgap PSCs.

Degradation of perovskite solar cells with excess PbI₂ is investigated. Excess PbI₂ in perovskite films undergoes photodecomposition (photolysis) under illumination, which produces lead and iodine and accelerates the degradation of PSCs.

Abstract

Excess/unreacted lead iodide (PbI₂) has been commonly used in perovskite films for the state‐of‐the‐art solar cell applications. However, an understanding of intrinsic degradation mechanisms of perovskite solar cells (PSCs) containing unreacted PbI₂ has been still insufficient and, therefore, needs to be clarified for better operational durability. Here, it is shown that degradation of PSCs is hastened by unreacted PbI₂ crystals under continuous light illumination. Unreacted PbI₂ undergoes photodecomposition under illumination, resulting in the formation of lead and iodine in films. Thus, this photodecomposition of PbI₂ is one of the main reasons for accelerated device degradation. Therefore, this work reveals that carefully controlling the formation of unreacted PbI₂ crystals in perovskite films is very important to improve device operational stability for diverse opto‐electronic applications in the future.

A new S‐atom‐containing small molecule (TPE‐S) is introduced as a dopant‐free hole‐transporting layer in all‐inorganic and organic/inorganic hybrid perovskite solar cells (PVSCs) with a p–i–n inverted structure, leading to improved power conversion efficiencies of 15.4% and 21%, respectively. In addition, these devices also show enhanced photostability, with performance comparable to state‐of‐the‐art PVSCs based on the conventional n–i–p structure.

Abstract

Designing new hole‐transporting materials (HTMs) with desired chemical, electrical, and electronic properties is critical to realize efficient and stable inverted perovskite solar cells (PVSCs) with a p–i–n structure. Herein, the synthesis of a novel 3D small molecule named TPE‐S and its application as an HTM in PVSCs are shown. The all‐inorganic inverted PVSCs made using TPE‐S, processed without any dopant or post‐treatment, are highly efficient and stable. Compared to control devices based on the commonly used HTM, PEDOT:PSS, devices based on TPE‐S exhibit improved optoelectronic properties, more favorable interfacial energetics, and reduced recombination due to an improved trap passivation effect. As a result, the all‐inorganic CsPbI₂Br PVSCs based on TPE‐S demonstrate a remarkable efficiency of 15.4% along with excellent stability, which is the one of the highest reported values for inverted all‐inorganic PVSCs. Meanwhile, the TPE‐S layer can also be generally used to improve the performance of organic/inorganic hybrid inverted PVSCs, which show an outstanding power conversation efficiency of 21.0%, approaching the highest reported efficiency for inverted PVSCs. This work highlights the great potential of TPE‐S as a simple and general dopant‐free HTM for different types of high‐performance PVSCs.

The built‐in electric field of a perovskite solar cell is reinforced by introducing electric dipole molecules, and the oriented charge transfer and collection are significantly improved. An efficiency of 21.5% is demonstrated and the average stability of NMFL device retains 95% PCE after storing over 2000 h under ambient conditions.

Abstract

Perovskite solar cells (PSCs) have received great attention due to their outstanding performance and their low processing costs. To boost their performance, one approach is to reinforce the built‐in electric field (BEF) to promote oriented carrier transport. The BEF is maximized by reinforcing the work function difference between cathode and anode (Δμ₁) and increasing the work function difference between lower and upper surfaces of perovskite film (Δμ₂) via introduction of electric dipole molecules, denoted as PTFCN and CF3BACl. The synergistic reinforcement of BEF improves charge transport and collection, and realizes markedly high photovoltaic performances with the best power conversion efficiency (PCE) up to 21.5%, a growth of 15.6% as compared to the control device, which is higher than the superposition of improvements achieved by either raising Δμ₁ or Δμ₂. Importantly, dual‐functional CF3BACl not only supplies dipole effect for tuning the surface potential of perovskite but offers hydrophobic trifluoride group toward the long‐term stable unencapsulated PSCs retaining more than 95% PCE after storing 2000 h under ambient conditions. This work demonstrates the synergistic effect of Δμ₁ and Δμ₂, providing an effective strategy for the further development of PSC in terms of photovoltaic conversion and stability.

A unique ammonium salt, 1‐naphthylmethylamine iodide (NMAI) is shown to passivate the surface defects of perovskite, induce upward energy level bending and block electrons at the interface between the perovskite and hole transport layer in perovskite solar cells. These combined effects result in reduced non‐radiative recombination. Hence, more intensified electroluminescence and a champion open‐circuit voltage of 1.20 V are achieved in NMAI‐based devices.

Abstract

The presence of non‐radiative recombination at the perovskite surface/interface limits the overall efficiency of perovskite solar cells (PSCs). Surface passivation has been demonstrated as an efficient strategy to suppress such recombination in Si cells. Here, 1‐naphthylmethylamine iodide (NMAI) is judiciously selected to passivate the surface of the perovskite film. In contrast to the popular phenylethylammonium iodide, NMAI post‐treatment primarily leaves NMAI salt on the surface of the perovskite film. The formed NMAI layer not only efficiently decreases the defect‐assisted recombination for chemical passivation, but also retards the charge accumulation of energy level mis‐alignment for vacuum level bending and prevents minority carrier recombination due to the charge‐blocking effect. Consequently, planar PSCs with high efficiency of 21.04% and improved long‐term stability (98.9% of the initial efficiency after 3240 h) are obtained. Moreover, open‐circuit voltage as high as 1.20 V is achieved at the absorption threshold of 1.61 eV, which is among the highest reported values in planar PSCs. This work provides new insights into the passivation mechanisms of organic ammonium salts and suggests future guidelines for developing improved passivation layers.