Covalently Functionalized SWCNTs as Tailored p-Type Dopants for Perovskite Solar Cells

p-Type Functionalized Carbon Nanohorns and Nanotubes in Perovskite Solar Cells

The incorporation of p-type functionalized carbon nanohorns (CNHs) in perovskite solar cells (PSCs) and their comparison with p-type functionalized single- and double-walled carbon nanotubes (SWCNTs and DWCNTs) are reported in this study for the first time. These p-type functionalized carbon nanomaterial (CNM) derivatives were successfully synthesized by [2 + 1] cycloaddition reaction with nitrenes formed from triphenylamine (TPA) and 9-phenyl carbazole (Cz)-based azides, yielding CNHs-TPA, CNHs-Cz, SWCNTs-Cz, SWCNTs-TPA, DWCNTs-TPA, and DWCNTs-Cz. These six novel CNMs were incorporated into the spiro-OMeTAD-based hole transport layer (HTL) to evaluate their impact on regular mesoporous PSCs. The photovoltaic results indicate that all p-type functionalized CNMs significantly improve the power conversion efficiency (PCE), mainly by enhancing the short-circuit current density (Jsc) and fill factor (FF). TPA-functionalized derivatives increased the PCE by 12-17% compared to the control device without CNMs, while Cz-functionalized derivatives resulted in a PCE increase of 4-8%. Devices prepared with p-type functionalized CNHs exhibited a slightly better PCE compared with those based on SWCNTs and DWCNTs derivatives. The increase in hole mobility of spiro-OMeTAD, additional p-type doping, better energy alignment with the perovskite layer, and enhanced morphology and contact interface play important roles in enhancing the performance of the device. Furthermore, the incorporation of p-type functionalized CNMs into the spiro-OMeTAD layer increased device stability by improving the hydrophobicity of the layer and enhancing the hole transport across the MAPI/spiro-OMeTAD interface. After 28 days under ambient conditions and darkness, TPA-functionalized CNMs maintained the performance of the device by over 90%, while Cz-functionalized CNMs preserved it between 75 and 85%.

Promotion Strategies of Hole Transport Materials by Electronic and Steric Controls for n-i-p Perovskite Solar Cells

Hole transport materials (HTMs) play a requisite role in n-i-p perovskite solar cells (PSCs). The properties of HTMs, such as hole extraction efficiency, chemical compatibility, film morphology, ion migration barrier, and so on, significantly affect PSCs' power conversion efficiencies (PCEs) and stabilities. Up till now, researchers have devoted much attention to developing new types of HTMs as well as promoting pristine HTMs using numerous strategies. In this Review, we summarize the design strategies of various common HTMs for n-i-p PSCs are comprehensively discussed from two separate aspects (additive and non-additive engineering). Additive engineering generally tunes electronic properties of HTMs while non-additive engineering basically modifies their steric structures. Critical analysis and comparison between these design strategies are provided, considering the overall PCEs and stabilities of PSCs. Finally, a brief perspective on future promising design strategies for HTMs is given, in order to fabricate efficient and stable n-i-p devices for the commercialization of PSCs.

Highly sensitive and selective determination of p-nitrophenol at an interpenetrating networks structure of self-assembled rod-like lanthanum hydroxide-oxidized multi-walled carbon nanotubes nanocomposite

In this study, a novel electrochemical sensor based on self-assembled rod-like lanthanum hydroxide-oxidized multi-walled carbon nanotubes (La(OH)₃-OxMWCNTs) nanocomposite was developed for sensitive determination of p-nitrophenol (p-NP). The La(OH)₃-OxMWCNTs nanocomposite with an interpenetrating networks structure was characterized by field emission electron microscope (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, Raman spectra and X-ray photoelectron spectroscopy (XPS). The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were performed to study the electrochemical behaviors of La(OH)₃-OxMWCNTs modified glassy carbon electrode (La(OH)₃-OxMWCNTs/GCE). The La(OH)₃-OxMWCNTs/GCE was used for sensitive determination of p-NP by CV and linear sweep voltammetry (LSV). Under the optimum conditions, the peak currents of LSV versus the concentrations of p-NP in the range 1.0-30.0 μmol L^-1 showed a good linear relationship (R²=0.9971), and the limit of detection (LOD) was calculated to be 0.27 μmol L^-1 (signal-to-noise ratio of 3, S/N=3). The recoveries of p-NP in real samples of industrial wastewater and Xiangjiang water at La(OH)₃-OxMWCNTs/GCE were in the range of 95.62-110.75% with relative standard deviation (RSD) in the range of 1.65-3.85%. The intra-day and inter-day precisions were estimated to be less than 2.76% (n= 5), indicating that La(OH)₃-OxMWCNTs/GCE possessed highly stability. In addition, La(OH)₃-OxMWCNTs/GCE sensor showed good anti-interference ability for determination of p-NP in aqueous mixtures containing high concentrations of inorganic and organic interferents, and a decrease of oxidation peak currents by less than 3.57% relative to the initial levels indicated it possessed excellent selectivity. Therefore, La(OH)₃-OxMWCNTs/GCE could be used as a fast, selective and sensitive electrochemical sensor platform for the selective determination and quantification of aqueous p-NP.

Blisters on graphite surface: a scanning microwave microscopy investigation

Scanning microwave microscopy (SMM) is based on the interaction between a sample and an electromagnetic evanescent field, in the microwave frequency range. SMM is usually coupled with a scanning probe microscopy (SPM) technique such as in our case, a scanning tunneling microscope (STM). In this way, the STM tip is used to control the distance between the probe and the sample while acting as an antenna for the microwave field. Thanks to the peculiarity of our home-made setup, the SMM is a suitable method to study blisters formed on HOPG surface as consequence of an electrochemical treatment. Our system has a “broad-band” approach that opens the way to perform local microwave spectroscopy over a broad frequency range. Moreover, microwaves have the ability to penetrate into the sample allowing the sub-surface characterization of materials. The application of the SMM to characterize blisters formed on the HOPG surface provides information on the sub-layer structures.

Blisters formed on an electrochemically treated HOPG are investigated by Scanning Microwave Microscopy that allows a spectroscopic and sub-surface characterization.

Highly Efficient Deep-UV Light-Emitting Diodes Using AlN-Based Deep-UV-Transparent Glass Electrodes

Many studies have set out to develop electrodes that are both highly conductive and transparent across a wide spectral region, from visible to deep UV (DUV). However, few solutions have been proposed because these two properties are mutually exclusive. In this paper, an AlN-based glass electrode film with a conducting filament formed by the application of an ac pulse is proposed as a solution, which exhibits a high transmittance in the DUV region (over 95.6% at 280 nm) and a low contact resistance with a p-Al_0.4Ga_0.6N layer (ρ_c = 3.2 × 10^-2 Ω·cm²). The Ohmic conduction mechanism at the interface between the AlN film and the p-Al_0.4Ga_0.6N layers is fully examined using various analytical tools. This AlN film is finally applied to a 280 nm top-emitting light-emitting diode, to verify the validity of the method, which exhibits very stable operations with a forward voltage of 7.7 V at 20 mA, a light output power of 7.49 mW at 100 mA, and, most importantly, a record high external quantum efficiency of 2.8% after packaging.