Development of Morphologically engineered Flower-like Hafnium-Doped ZnO with Experimental and DFT Validation for Low-Temperature and Ultrasensitive Detection of NOX Gas.

Substitutional doping and different nanostructures of ZnO have rendered it an effective sensor for the detection of volatile organic compounds in real-time atmosphere. However, the low selectivity of ZnO sensors limits their applications. Herein, hafnium (Hf)-doped ZnO (Hf-ZnO) nanostructures are developed by the hydrothermal method for high selectivity of hazardous NOX gas in the atmosphere, substantially portraying the role of doping concentration on the enhancement of structural, optical, and sensing behavior. ZnO microspheres with 5% Hf doping showed excellent sensing and detected 22 parts per billion (ppb) NOX gas in the atmosphere, within 24 s, which is much faster than ZnO (90 s), and rendered superior sensing ability (S = 67) at a low temperature (100 °C) compared to ZnO (S = 40). The sensor revealed exceptional stability under humid air (S = 55 at 70% RH), suggesting a potential of 5% Hf-ZnO as a new stable sensing material. Density functional theory (DFT) and other characterization analyses revealed that the high sensing activity of 5% Hf-ZnO is attributed to the accessibility of more adsorption sites arising due to charge distortion, increased oxygen vacancies concentration, Lewis acid base, porous morphology, small particle size (5 nm), and strong bond interaction amidst NO2 molecule with ZnO-Hf-Ovacancy sites, resulting from the substitution of the host cation (Zn2+) with doping cation (Hf4+).

Cotton soot derived carbon nanoparticles for NiO supported processing temperature tuned ambient perovskite solar cells.

The emergence of perovskite solar cells (PSCs) in a "catfish effect" of other conventional photovoltaic technologies with the massive growth of high-power conversion efficiency (PCE) has given a new direction to the entire solar energy field. Replacing traditional metal-based electrodes with carbon-based materials is one of the front-runners among many other investigations in this field due to its cost-effective processability and high stability. Carbon-based perovskite solar cells (c-PSCs) have shown great potential for the development of large scale photovoltaics. First of its kind, here we introduce a facile and cost-effective large scale carbon nanoparticles (CNPs) synthesis from mustard oil assisted cotton combustion for utilization in the mesoporous carbon-based perovskite solar cell (PSC). Also, we instigate two different directions of utilizing the carbon nanoparticles for a composite high temperature processed electrode (HTCN) and a low temperature processed electrode (LTCN) with detailed performance comparison. NiO/CNP composite thin film was used in high temperature processed electrodes, and for low temperature processed electrodes, separate NiO and CNP layers were deposited. The HTCN devices with the cell structure FTO/c-TiO2/m-TiO2/m-ZrO2/high-temperature NiO-CNP composite paste/infiltrated MAPI (CH3NH3PbI3) achieved a maximum PCE of 13.2%. In addition, high temperature based carbon devices had remarkable stability of ~ 1000 h (ambient condition), retaining almost 90% of their initial efficiency. In contrast, LTCN devices with configuration FTO/c-TiO2/m-TiO2/m-ZrO2/NiO/MAPI/low-temperature CNP had a PCE limit of 14.2%, maintaining ~ 72% of the initial PCE after 1000 h. Nevertheless, we believe this promising approach and the comparative study between the two different techniques would be highly suitable and adequate for the upcoming cutting-edge experimentations of PSC.

Realization of Poly(methyl methacrylate)-Encapsulated Solution-Processed Carbon-Based Solar Cells: An Emerging Candidate for Buildings' Comfort.

The self-assembling characteristics allow carbon nanomaterials to be readily explored, environmentally benign, solution-processed, low-cost, and efficient solar light-harvesting materials. An effort has been made to replace the regular photovoltaic device's electrodes by different carbon allotrope-based electrodes. Sequential fabrication of carbon solar cells (SCs) was performed under ambient conditions, where FTO/graphene/single-walled carbon nanotubes/graphene quantum dots-fullerene/carbon black paste layers were assembled with poly(methyl methacrylate) (PMMA) as an encapsulating layer. The PMMA layer provides significant improvement toward the entry of water vapor, hence leading to stability up to 1000 h. The photoconversion efficiency of the PMMA-encapsulated carbon SC has been increased by ∼105% and the stability decreased by only ∼10% after 1000 h of exposure to environmental moisture. Besides, the building integrated photovoltaic window properties achieved using this carbon SC were also investigated by using the color rendering index and the correlated color temperature, which can have an impact on the buildings' occupants' comfort. This study leads to an extensive integration to improve carbon-based materials because of their effective and useful but less-explored characteristics suitable for potential photovoltaic applications.

Performance of WO3-Incorporated Carbon Electrodes for Ambient Mesoscopic Perovskite Solar Cells.

The stability of perovskite solar cells (PSC) is often compromised by the organic hole transport materials (HTMs). We report here the effect of WO3 as an inorganic HTM for carbon electrodes for improved stability in PSCs, which are made under ambient conditions. Sequential fabrication of the PSC was performed under ambient conditions with mesoporous TiO2/Al2O3/CH3NH3PbI3 layers, and, on the top of these layers, the WO3 nanoparticle-embedded carbon electrode was used. Different concentrations of WO3 nanoparticles as HTM incorporated in carbon counter electrodes were tested, which varied the stability of the cell under ambient conditions. The addition of 7.5% WO3 (by volume) led to a maximum power conversion efficiency of 10.5%, whereas the stability of the cells under ambient condition was ∼350 h, maintaining ∼80% of the initial efficiency under light illumination. At the same time, the higher WO3 concentration exhibited an efficiency of 9.5%, which was stable up to ∼500 h with a loss of only ∼15% of the initial efficiency under normal atmospheric conditions and light illumination. This work demonstrates an effective way to improve the stability of carbon-based perovskite solar cells without affecting the efficiency for future applications.

Enhanced Efficiency of Carbon-Based Mesoscopic Perovskite Solar Cells through a Tungsten Oxide Nanoparticle Additive in the Carbon Electrode.

This paper presents perovskite solar cells employed with WO3 nanoparticles embedded carbon top electrode. WO3 nanoparticles works as an inorganic hole-transport material (HTM) to promote the hole-extraction in the perovskite/carbon interface as revealed by efficiency, electrochemical impedance and external quantum efficiency measurements. As a result, a 40% enhancement of energy conversion efficiency has been achieved compared to the reference devices with the energy conversion efficiency of 10.77% under standard conditions. In addition, the Li-TFSI can modify the interface between electron-transport material (ETM) and perovskite, which may inhibit the recombination at the ETM/perovskite interface. The VOC of devices upon the modification of Li-TFSI is increased from 887.9 to 934.2 mV. This work highlights about the enlightenment of the effective performance of carbon-based mesoscopic PSCs by the introduction of HTM and the modification of interfaces.