Octadecylamine‐Functionalized Single‐Walled Carbon Nanotubes for Facilitating the Formation of a Monolithic Perovskite Layer and Stable Solar Cells

Organic–inorganic lead halide perovskites have shown great future for application in solar cells owing to their exceptional optical and electronic properties. To achieve high‐performance perovskite solar cells, a perovskite light absorbing layer with large grains is desirable in order to minimize grain boundaries and recombination during the operation of the device. Herein, a simple yet efficient approach is developed to synthesize perovskite films consisting of monolithic‐like grains with micrometer size through in situ deposition of octadecylamine functionalized single‐walled carbon nanotubes (ODA‐SWCNTs) onto the surface of the perovskite layer. The ODA‐SWCNTs form a capping layer that controls the evaporation rate of organic solvents in the perovskite film during the postthermal treatment. This favorable morphology in turn dramatically enhances the short‐circuit current density of the perovskite solar cells and almost completely eliminates the hysteresis. A maximum power conversion efficiency of 16.1% is achieved with an ODA‐SWCNT incorporated planar solar cell using (FA_0.83MA_0.17)_0.95Cs_0.05Pb(I_0.83Br_0.17)₃ as light absorber. Furthermore, the perovskite solar cells with ODA‐SWCNT demonstrate extraordinary stability with performance retention of 80% after 45 d stability testing under high humidity (60–90%) environment. This work opens up a new avenue for morphology manipulation of perovskite films and enhances the device stability using carbon material.     

Microwave‐Induced Controlled Purification of Single‐Walled Carbon Nanotubes without Sidewall Functionalization

A microwave‐induced controlled method for the purification of single‐walled carbon nanotubes (SWCNTs) by removing residual metal catalysts and carbonaceous impurities is reported. Compared to conventional strong acid treatment, this one‐step method uses dilute acids and complexing agents and reduces the reaction times to the order of minutes. Furthermore, the SWCNTs retain their chemical and physical properties and are not functionalized. Electron microscopy, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and atomic absorption (AA) spectrometry studies were used to characterize the purified SWCNTs.     

Recent Advances in Applications of Sorted Single‐Walled Carbon Nanotubes

Single‐walled carbon nanotubes (SWCNTs) exhibit outstanding properties that make them appealing in a wide range of applications. However, their properties are variable depending on the tube helicity (chirality), which has been a challenge for a long time and needs to be effectively controlled. In recent years, tremendous efforts have been made to control the electrical type/chirality of nanotubes through both direct controlled synthesis and postsynthesis separation methods. Driven by these breakthroughs, the applications of separated families of SWCNTs in various fields have emerged as a new topic of research. In this Review, an overview of recent advances in the use of highly purified and well‐separated SWCNTs in a comprehensive range of applications is presented including photovoltaics, transistors, batteries, sensors, light emitters, biological/medical fields, and others. Finally, important future directions for the utilization of separated SWCNTs in these fields are provided.     

Spin‐ and Spray‐Deposited Single‐Walled Carbon‐Nanotube Electrodes for Organic Solar Cells

Organic bulk‐heterojunction solar cells using thin‐film single‐walled carbon‐nanotube (SWCNT) anodes deposited on glass are reported. Two types of SWCNT films are investigated: spin‐coated films from dichloroethane (DCE), and spray‐coated films from deionized water using sodium dodecyl sulphate (SDS) or sodium dodecyl benzene sulphonate (SDBS) as the surfactant. All of the films are found to be mechanically robust, with no tendency to delaminate from the underlying substrate during handling. Acid treatment with HNO₃ yields high conductivities >1000 S cm^?1 for all of the films, with values of up to 7694 ± 800 S cm^?1 being obtained when using SDS as the surfactant. Sheet resistances of around 100 Ω sq^?1 are obtained at reasonable transmission, for example, 128 ± 2 Ω sq^?1 at 90% for DCE, 57 ± 3 Ω sq^?1 at 65% for H₂O:SDS, and 68 ± 5 Ω sq^?1 at 70% for H₂O:SDBS. Solar cells are fabricated by successively coating the SWCNT films with poly(3,4‐ethylenedioxythiophene):poly(styrene sulphonate) (PEDOT:PSS), a blend of regioregular poly(3‐hexylthiophene) (P3HT) and 1‐(3‐methoxy‐carbonyl)‐propyl‐1‐phenyl‐(6,6)C₆₁ (PCBM), and LiF/Al. The resultant devices have respective power conversions of 2.3, 2.2 and 1.2% for DCE, H₂O:SDS and H₂O:SDBS, with the first two being at a virtual parity with reference devices using ITO‐coated glass as the anode (2.3%).     

Selective Enhancement of Photoluminescence in Filled Single‐Walled Carbon Nanotubes

The insertion of organometallic molecules into the hollow core of single‐walled carbon nanotubes can drastically change their properties. Using biocompatible standardized suspensions of pristine, opened, and filled nanotubes, a very selective enhancement of the photoluminescence and optical absorption is observed. Via ferrocene encapsulation, the PL signal increases almost by a factor of three for tubes with chiralities such as (8,6) and (9,5). This behavior is attributed to a local electron charge transfer from the ferrocene molecules that balances out the p‐type doping of the nanotubes resulting from the modified charge distribution of the surfactant molecules and the opening process. The near infrared photoluminescence of the nanotubes in solution is strongly enhanced when ferrocene is encapsulated. The diameter‐dependent charge transfer is additionally confirmed by first principles calculations. These findings highlight an essential ingredient to optimize the application of solvated nanotubes, for instance, as in–vivo near infrared sensors in biomedical research.     

Carbon Nanotube Based Inverted Flexible Perovskite Solar Cells with All‐Inorganic Charge Contacts

Organolead halide perovskite solar cells (PSC) are arising as promising candidates for next‐generation renewable energy conversion devices. Currently, inverted PSCs typically employ expensive organic semiconductor as electron transport material and thermally deposited metal as cathode (such as Ag, Au, or Al), which are incompatible with their large‐scale production. Moreover, the use of metal cathode also limits the long‐term device stability under normal operation conditions. Herein, a novel inverted PSC employs a SnO₂‐coated carbon nanotube (SnO₂@CSCNT) film as cathode in both rigid and flexible substrates (substrate/NiO‐perovskite/Al₂O₃‐perovskite/SnO₂@CSCNT‐perovskite). Inverted PSCs with SnO₂@CSCNT cathode exhibit considerable enhancement in photovoltaic performance in comparison with the devices without SnO₂ coating owing to the significantly reduced charge recombination. As a result, a power conversion efficiency of 14.3% can be obtained on rigid substrates while the flexible ones achieve 10.5% efficiency. More importantly, SnO₂@CSCNT‐based inverted PSCs exhibit significantly improved stability compared to the standard inverted devices made with silver cathode, retaining over 88% of their original efficiencies after 550 h of full light soaking or thermal stress. The results indicate that SnO₂@CSCNT is a promising cathode material for long‐term device operation and pave the way toward realistic commercialization of flexible PSCs.     

Selective Electrochemical Etching of Single‐Walled Carbon Nanotubes

Single‐walled carbon nanotubes (SWNTs) are a promising material for future nanotechnology. However, their applications are still limited in success because of the co‐existence of metallic SWNTs and semiconducting SWNTs produced samples. Here, electrochemical etching, which shows both diameter and electrical selectivity, is demonstrated to remove SWNTs. With the aid of a back‐gate electric field, selective removal of metallic SWNTs is realized, resulting in high‐performance SWNT field‐effect transistors with pure semiconducting SWNT channels. Moreover, electrochemical etching is realized on a selective area. These findings would be valuable for research and the application of SWNTs in electrochemistry and in electronic devices.     

Alloy Engineering in Few‐Layer Manganese Phosphorus Trichalcogenides for Surface‐Enhanced Raman Scattering

Manganese phosphorus trichalcogenides are widely used in the field of photocatalysis and magnetic studies due to their broadband gaps. Herein, an alloy engineering method for the few‐layer manganese phosphorus trichalcogenides (MnPS_3–xSe_x, 0 ≤ x ≤ 3) in surface‐enhanced Raman scattering (SERS) is reported. A new strategy, with the coupling of exciton resonance (µ_ex) and photoinduced charge transfer (PICT), is applied to screen out materials for SERS enhancement. According to the calculation of density functional theory, the bandgap of manganese phosphorus trichalcogenides (MnPS₃) can be adjusted to match the band energy of Rhodamine 6G molecules by alloy engineering. Furthermore, a series of few‐layer MnPS_3–xSe_x (0 ≤ x ≤ 3) are fabricated to study the PICT‐induced SERS behavior under resonance excitation. The good performance with a detection limit down to 10^?9 m indicates that the synergistic resonances between µ_ex and PICT are crucial to the enhancement.     

An Ultrathin Flexible 2D Membrane Based on Single‐Walled Nanotube–MoS2 Hybrid Film for High‐Performance Solar Steam Generation

Solar steam generation is achieved by localized heating system using various floating photothermal materials. However, the steam generation efficiency is hindered by the difficulty in obtaining a photothermal material with ultrathin structure yet sufficient solar spectrum absorption capability. Herein, for the first time, an ultrathin 2D porous photothermal film based on MoS₂ nanosheets and single‐walled nanotube (SWNT) films is prepared. The as‐prepared SWNT–MoS₂ film exhibits an absorption of more than 82% over the whole solar spectrum range even with an ultrathin thickness of ≈120 nm. Moreover, the SWNT–MoS₂ film floating on the water surface can generate a sharp temperature gradient due to the localized heat confinement effect. Meanwhile, the ultrathin and porous structure effectively facilitates the fast water vapor escaping, consequently an impressively high evaporation efficiency of 91.5% is achieved. Additionally, the superior mechanical strength of the SWNT–MoS₂ film enables the film to be reused for atleast 20 solar illumination cycles and maintains stable water productivity as well as high salt rejection performance. This rational designed hybrid architecture provides a novel strategy for constructing 2D‐based nanomaterials for solar energy harvesting, chemical separation, and related technologies.     

Incorporating Graphitic Carbon Nitride (g‐C3N4) Quantum Dots into Bulk‐Heterojunction Polymer Solar Cells Leads to Efficiency Enhancement

Graphitic carbon nitride (g‐C₃N₄) has been commonly used as photocatalyst with promising applications in visible‐light photocatalytic water‐splitting. Rare studies are reported in applying g‐C₃N₄ in polymer solar cells. Here g‐C₃N₄ is applied in bulk heterojunction (BHJ) polymer solar cells (PSCs) for the first time by doping solution‐processable g‐C₃N₄ quantum dots (C₃N₄ QDs) in the active layer, leading to a dramatic efficiency enhancement. Upon C₃N₄ QDs doping, power conversion efficiencies (PCEs) of the inverted BHJ‐PSC devices based on different active layers including poly(3‐hexylthiophene‐2,5‐diyl):[6,6]‐phenyl‐C61‐butyric acid methyl ester (P3HT:PC₆₁BM), poly(4,8‐bis‐alkyloxybenzo(l,2‐b:4,5‐b′)dithiophene‐2,6‐diylalt‐(alkyl thieno(3,4‐b)thiophene‐2‐carboxylate)‐2,6‐diyl):[6,6]‐phenyl C₇₁‐butyric acid methyl ester (PBDTTT‐C:PC₇₁BM), and poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐co‐3‐fluorothieno [3,4‐b]thiophene‐2‐carboxylate] (PTB7‐Th):PC₇₁BM reach 4.23%, 6.36%, and 9.18%, which are enhanced by ≈17.5%, 11.6%, and 11.8%, respectively, compared to that of the reference (undoped) devices. The PCE enhancement of the C₃N₄ QDs doped BHJ‐PSC device is found to be primarily attributed to the increase of short‐circuit current (J_sc), and this is confirmed by external quantum efficiency (EQE) measurements. The effects of C₃N₄ QDs on the surface morphology, optical absorption and photoluminescence (PL) properties of the active layer film as well as the charge transport property of the device are investigated, revealing that the efficiency enhancement of the BHJ‐PSC devices upon C₃N₄ QDs doping is due to the conjunct effects including the improved interfacial contact between the active layer and the hole transport layer due to the increase of the roughness of the active layer film, the facilitated photoinduced electron transfer from the conducting polymer donor to fullerene acceptor, the improved conductivity of the active layer, and the improved charge (hole and electron) transport.     

Tuning Electrical Conductance of Serpentine Single‐Walled Carbon Nanotubes

Changes in resistivity of serpentine single‐walled carbon nanotubes are presented as a function of bending radius, r_b, in the range of 100–2000 nm. Resistivity (ρ) is observed to increase with curvature (1/r_b), which is consistent with theoretical speculation on strain‐induced bandgap increment. Furthermore, a sharp bend (r_b < 50nm) in the nanotubes results in a drastic change in the field‐effect behavior, i.e., from ambipolar to p type across the bend. Local Raman spectra show that the G‐band Raman frequencies shift along the curvature, which may be attributed to local deformation and broken cylindrical symmetry in the nanotubes. The results suggest the possibility to tune the electrical properties by bending nanotubes and to build an all‐nanotube device by modulating the structure of the same tube.     

Carbon Nanotube–Graphitic Carbon Nitride Hybrid Films for Flavoenzyme‐Catalyzed Photoelectrochemical Cells

In green plants, solar‐powered electrons are transferred through sophistically arranged photosystems and are subsequently channelled into the Calvin cycle to generate chemical energy. Inspired by the natural photosynthetic scheme, a photoelectrochemical cell (PEC) is constructed configured with protonated graphitic carbon nitride (p‐g‐C₃N₄) and carbon nanotube hybrid (CNT/p‐g‐C₃N₄) film cathode, and FeOOH‐deposited bismuth vanadate (FeOOH/BiVO₄) photoanode for the production of industrially useful chiral alkanes using an old yellow enzyme homologue from Thermus scotoductus (TsOYE). In the biocatalytic PEC platform, photoexcited electrons provided by the FeOOH/BiVO₄ photoanode are transferred to the robust and self‐standing CNT/p‐g‐C₃N₄ hybrid film that electrocatalytically reduces flavin mononucleotide (FMN) mediator. The p‐g‐C₃N₄ promotes a two‐electron reduction of FMN coupled with an accelerated electron transfer by the conductive CNT network. The reduced FMN subsequently delivers the electrons to TsOYE for the highly enantioselective conversion of ketoisophorone to (R)‐levodione. Under light illumination (>420 nm) and external bias, (R)‐levodione is synthesized with the enantiomeric excess value of above 83%, not influenced by the scale of applied bias, simultaneously exhibiting stable and high current efficiency. The results suggest that the biocatalytic PEC made up of economical materials can selectively synthesize high‐value organic chemicals using water as an electron donor.     

Boosting Perovskite Solar Cells Performance and Stability through Doping a Poly‐3(hexylthiophene) Hole Transporting Material with Organic Functionalized Carbon Nanostructures

Perovskite solar cells (PSCs) are demonstrating great potential to compete with second generation photovoltaics. Nevertheless, the key issue hindering PSCs full exploitation relies on their stability. Among the strategies devised to overcome this problem, the use of carbon nanostructures (CNSs) as hole transporting materials (HTMs) has given impressive results in terms of solar cells stability to moisture, air oxygen, and heat. Here, the use of a HTM based on a poly(3‐hexylthiophene) (P3HT) matrix doped with organic functionalized single walled carbon nanotubes (SWCNTs) and reduced graphene oxide in PSCs is proposed to achieve higher power conversion efficiencies (η = 11% and 7.3%, respectively) and prolonged shelf‐life stabilities (480 h) in comparison with a benchmark PSC fabricated with a bare P3HT HTM (η = 4.3% at 480 h). Further endurance test, i.e., up to 3240 h, has shown the failure of all the PSCs based on undoped P3HT, while, on the contrary, a η of ≈8.7% is still detected from devices containing 2 wt% SWCNT‐doped P3HT as HTM. The increase in photovoltaic performances and stabilities of the P3HT‐CNS‐based solar cell, with respect to the standard P3HT‐based one, is attributed to the improved interfacial contacts between the doped HTM and the adjacent layers.     

Aligning Single‐Walled Carbon Nanotubes By Means Of Langmuir–Blodgett Film Deposition: Optical,Morphological, and Photo‐electrochemical Studies

An alkoxy‐substituted poly(phenylene thiophene) is used in order to suspend single‐walled carbon nanotubes in an organic solvent. The suspension is spread on the air–water interface of a Langmuir trough and the floating film is characterized by means of Brewster angle microscopy and UV‐visible reflection spectroscopy and the compression isotherm is recorded. The polymer/carbon‐nanotube blend is transferred onto different substrates using the Langmuir–Blodgett technique. AFM measurements indicate the formation of globular structures for the samples transferred at low surface‐pressure values and a tubular morphology for high‐pressure‐deposited samples. AFM analysis is repeated on a sample exposed to soft X‐rays for about 5 h and a highly organized structure of bundles of carbon nanotubes rises up. Samples with different numbers of layers are transferred onto ITO substrates by means of the Langmuir–Blodgett method and are tested as photocathodes in a photo‐electrochemical cell. A V_oc of 0.18 V, an I_sc of 85.8 mA, FF of 40.0%, and η of (6.23 × 10^?3)% are obtained.     

Electrochemical Properties of High‐Power Supercapacitors Using Single‐Walled Carbon Nanotube Electrodes

We have investigated the key factors determining the performance of supercapacitors constructed using single‐walled carbon nanotube (SWNT) electrodes. Several parameters, such as composition of the binder, annealing temperature, type of current collector, charging time, and discharging current density have been optimized for the best performance of the supercapacitor with respect to energy density and power density. We find a maximum specific capacitance of 180 F/g and a measured power density of 20 kW/kg at energy densities in the range from 7 to 6.5 Wh/kg at 0.9 V in a solution of 7.5 N KOH (the currently available supercapacitors have energy densities in the range 6–7 Wh/kg and power density in the range 0.2–5 kW/kg at 2.3 V in non‐aqueous solvents).     

多晶黑硅表面微结构对电池效率的影响

采用Ag离子辅助化学刻蚀法制备了多晶黑硅薄片,使用NaOH溶液处理多晶黑硅表面,增大其表面纳米孔直径,使SiNx薄膜能够均匀覆盖整个黑硅表面,提高黑硅的钝化效果,进而提高多晶黑硅电池光电转化效率.通过反射谱仪、扫描电子显微镜(SEM)、太阳电池测试系统等测试和表征不同扩孔时间对多晶黑硅各方面性能的影响.结果表明:未被NaOH扩孔处理的多晶黑硅的反射率最低,为5.03％,多晶黑硅太阳电池的光电转化效率为16.51％.当多晶黑硅被NaOH腐蚀40 s时,反射率为10.01％,电池的效率为18.00％,比普通多晶硅太阳电池的效率高2.19％,比未被扩孔处理的多晶黑硅太阳电池的效率高1.49％.     

Three‐Dimensional Bulk Heterojunction Morphology for Achieving High Internal Quantum Efficiency in Polymer Solar Cells

Here, an investigation of three‐dimensional (3D) morphologies for bulk heterojunction (BHJ) films based on regioregular poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) is reported. Based on the results, it is demonstrated that optimized post‐treatment, such as solvent annealing, forces the PCBM molecules to migrate or diffuse toward the top surface of the BHJ composite films, which induces a new vertical component distribution favorable for enhancing the internal quantum efficiency (η_IQE ) of the devices. To investigate the 3D BHJ morphology, novel time‐of‐flight secondary‐ion mass spectroscopy studies are employed along with conventional methods, such as UV‐vis absorption, X‐ray diffraction, and high‐resolution transmission electron microscopy studies. The η_IQE of the devices are also compared after solvent annealing for different times, which clearly shows the effect of the vertical component distribution on the performance of BHJ polymer solar cells. In addition, the fabrication of high‐performance P3HT:PCBM solar cells using the optimized solvent‐annealing method is reported, and these cells show a mean power‐conversion efficiency of 4.12% under AM 1.5G illumination conditions at an intensity of 100 mW cm^?2.     

Over 16.7% Efficiency Organic‐Silicon Heterojunction Solar Cells with Solution‐Processed Dopant‐Free Contacts for Both Polarities

Realization of synchronous improvement in optical management and electrical engineering is necessary to achieve high‐performance photovoltaic device. However, inherent challenges are faced in organic‐silicon heterojunction solar cells (HSCs) due to the poor contact property of polymer on structured silicon surface. Herein, a remarkable efficiency boost from 12.6% to over 16.7% in poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)/n‐silicon (PEDOT:PSS/n‐Si) HSCs by independent optimization of hole‐/electron‐selective contacts only relying on solution‐based processes is realized. A bilayer PEDOT:PSS film with different functionalizations is utilized to synchronously realize conformal contact and effective carrier collection on textured Si surface, making the photogenerated carriers be well separated at heterojunction interface. Meanwhile, fullerene derivative is used as electron‐transporting layer at the rear n‐Si/Al interface to reduce the contact barrier. The study of carriers' transport and independent optimization on separately contacted layers may lead to an effective and simplified path to fabricate high‐performance organic‐silicon heterojunction devices.     

Enhanced Thermal Stability and Efficiency of Polymer Bulk‐Heterojunction Solar Cells by Low‐Temperature Drying of the Active Layer

This study addresses two key issues, stability and efficiency, of polymer solar cells based on blended poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) by demonstrating a film‐forming process that involves low‐temperature drying (?5 °C) and subsequent annealing of the active layer. The low‐temperature process achieves 4.70% power conversion efficiency (PCE) and ～1250 h storage half‐life at 65 °C, which are significant improvements over the 3.39% PCE and ～143 h half‐life of the regular room‐temperature process. The improvements are attributed to the enhanced nucleation of P3HT crystallites as well as the minimized separation of the P3HT and PCBM phases at the low drying temperature, which upon post‐drying annealing results in a morphology consisting of small PCBM‐rich domains interspersed within a densely interconnected P3HT crystal network. This morphology provides ample bulk‐heterojunction area for charge generation while allowing for facile charge transport; moreover, the P3HT crystal network serves as an immobile frame at heating temperatures less than the melting point (T_m) of P3HT, thus preventing PCBM/P3HT phase separation and the corresponding device degradation.