Cs and Br tuning to achieve ultralow-hysteresis and high-performance indoor triple cation perovskite solar cell with low-cost carbon-based electrode.

With high efficacy for electron-photon conversion under low light, perovskite materials show great potential for indoor solar cell applications to power small electronics for internet of things (IoTs). To match the spectrum of an indoor LED light source, triple cation perovskite composition was varied to adjust band gap values via Cs and Br tuning. However, increased band gaps lead to morphology, phase instability, and defect issues. 10% Cs and 30% Br strike the right balance, leading to low-cost carbon-based devices with the highest power conversion efficiency (PCE) of 31.94% and good stability under low light cycles. With further improvement in device stack and size, functional solar cells with the ultralow hysteresis index (HI) of 0.1 and the highest PCE of 30.09% with an active area of 1 cm2 can be achieved. A module from connecting two such cells in series can simultaneously power humidity and temperature sensors under 1000 lux.

Efficient and Stable Carbon-Based Perovskite Solar Cells Enabled by Mixed CuPc:CuSCN Hole Transporting Layer for Indoor Applications.

Perovskite solar cells (PSCs) are an innovative technology with great potential to offer cost-effective and high-performance devices for converting light into electricity that can be used for both outdoor and indoor applications. In this study, a novel hole-transporting layer (HTL) was created by mixing copper phthalocyanine (CuPc) molecules into a copper(I) thiocyanate (CuSCN) film and was applied to carbon-based PSCs with cesium/formamidinium (Cs0.17FA0.83Pb(I0.83Br0.17)3) as a photoabsorber. At the optimum concentration, a high power conversion efficiency (PCE) of 15.01% was achieved under AM1.5G test conditions, and 32.1% PCE was acquired under low-light 1000 lux conditions. It was discovered that the mixed CuPc:CuSCN HTL helps reduce trap density and improve the perovskite/HTL interface as well as the HTL/carbon interface. Moreover, the PSCs based on the mixed CuPc:CuSCN HTL provided better stability over 1 year due to the hydrophobicity of CuPc material. In addition, thermal stability was tested at 85 °C and the devices achieved an average efficiency drop of approximately 50% of the initial PCE value after 1000 h. UV light stability was also examined, and the results revealed that the average efficiency drop of 40% of the initial value for 70 min of exposure was observed. The work presented here represents an important step toward the practical implementation of the PSC as it paves the way for the development of cost-effective, stable, yet high-performance PSCs for both outdoor and indoor applications.

Robust perovskite formation via vacuum thermal annealing for indoor perovskite solar cells.

Perovskite materials are fascinating candidates for the next-generation solar devices. With long charge carrier lifetime, metal-halide perovskites are known to be good candidates for low-light harvesting. To match the irradiance spectra of indoor light, we configured a triple-cation perovskite material with appropriate content of bromide and chloride (FA0.45MA0.49Cs0.06Pb(I0.62Br0.32Cl0.06)3) to achieve an optimum band gap (Eg) of [Formula: see text]1.80 eV. With low photon flux at indoor condition, minimal recombination is highly desirable. To achieve such goal, we, for the first time, combined dual usage of antisolvent deposition and vacuum thermal annealing, namely VTA, to fabricate a high-quality perovskite film. VTA leads to compact, dense, and hard morphology while suppressing trap states at surfaces and grain boundaries, which are key culprits for exciton losses. With low-cost carbon electrode architecture, VTA devices exhibited average power conversion efficiency (PCE) of 27.7 ± 2.7% with peak PCE of 32.0% (Shockley-Queisser limit of 50-60%) and average open-circuit voltage (Voc) of 0.93 ± 0.02 V with peak Voc of 0.96 V, significantly more than those of control and the vacuum treatment prior to heat.

Preparation and Characterization of Photoluminescent Graphene Quantum Dots from Watermelon Rind Waste for the Detection of Ferric Ions and Cellular Bio-Imaging Applications.

Graphene quantum dots (GQDs) were synthesized using watermelon rind waste as a photoluminescent (PL) agent for ferric ion (Fe3+) detection and in vitro cellular bio-imaging. A green and simple one-pot hydrothermal technique was employed to prepare the GQDs. Their crystalline structures corresponded to the lattice fringe of graphene, possessing amide, hydroxyl, and carboxyl functional groups. The GQDs exhibited a relatively high quantum yield of approximately 37%. Prominent blue emission under UV excitation and highly selective PL quenching for Fe3+ were observed. Furthermore, Fe3+ could be detected at concentrations as low as 0.28 µM (limit of detection), allowing for high sensitivity toward Fe3+ detection in tap and drinking water samples. In the bio-imaging experiment, the GQDs exhibited a low cytotoxicity for the HeLa cells, and they were clearly illuminated at an excitation wavelength of 405 nm. These results can serve as the basis for developing an environment-friendly, simple, and cost-effective approach of using food waste by converting them into photoluminescent nanomaterials for the detection of metal ions in field water samples and biological cellular studies.

Investigation of Functionalized Surface Charges of Thermoplastic Starch/Zinc Oxide Nanocomposite Films Using Polyaniline: The Potential of Improved Antibacterial Properties.

Improving the antibacterial activity of biodegradable materials is crucial for combatting widespread drug-resistant bacteria and plastic pollutants. In this work, we studied polyaniline (PANI)-functionalized zinc oxide nanoparticles (ZnO NPs) to improve surface charges. A PANI-functionalized ZnO NP surface was prepared using a simple impregnation technique. The PANI functionalization of ZnO successfully increased the positive surface charge of the ZnO NPs. In addition, PANI-functionalized ZnO improved mechanical properties and thermal stability. Besides those properties, the water permeability of the bionanocomposite films was decreased due to their increased hydrophobicity. PANI-functionalized ZnO NPs were applied to thermoplastic starch (TPS) films for physical properties and antibacterial studies using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The PANI-functionalized ZnO bionanocomposite films exhibited excellent antibacterial activity for both E. coli (76%) and S. aureus (72%). This result suggests that PANI-functionalized ZnO NPs can improve the antibacterial activity of TPS-based bionanocomposite films.

Alkali/zinc-activated fly ash nanocomposites for dye removal and antibacterial applications.

Fly ash (FA), obtained as waste materials from industrial power plants, is generated in large quantities and low recycling. In this study, re-generation of waste FA as cost-effective materials with adsorbent and antibacterial applications was assessed. Alkaline/zinc-activated fly ash nanocomposite (A-FA/Zn) was prepared using one-pot hydrothermal technique. Those nanocomposites are characterized by high surface area and negatively surface charge, which are important influences contributing to an enhancement in adsorption capacity via increase in the number of adsorptive sites and electrostatic interaction between dye molecules-nanocomposites. Additionally, the presence of Zn ions in the prepared nanocomposites represents a key advantage with respect to enhancing antibacterial activity. The feasibility of further enhancing adsorption and antibacterial mechanisms was also examined. It is anticipated that the findings of this study will provide useful information with respect to the development of simple, eco-friendly and low-cost A-FA/Zn with multifunctional applications as organic dye removal and antibacterial purposes.

Controlled Structure and Growth Mechanism behind Hydrothermal Growth of TiO2 Nanorods.

Fabrication of uniform vertically-aligned titanium dioxide nanorods (TiO2 NRs) was achieved by hydrothermal growth on a fluorine-doped tin oxide (FTO) glass substrate. The substrate was coated by a TiO2 seed layer composed of titanium (IV) butoxide (TBO) as a precursor in an HCl solution. To reduce the amount of toxic substances used in this work, a minimal amount of HCl was used. On a larger scale, this method would require less precursor and therefore be a cost-savings. The aim of the present work is to achieve high crystalline orientations of TiO2 NRs for low quantities of both TBO precursor and HCl solutions. Results showed that the 0.7% TBO TiO2 NRs after 1.5 h of hydrothermal treatment exhibited the optimal crystalline orientation along [001] while the (002) plane is the dominant facet. The results demonstrate high transmittance of visible light and well-formed crystalline structures that offer a fast electron pathway along the length of the TiO2 NRs with less grain boundaries. Lastly, TiO2 NRs and their growth mechanism are discussed. This work offers a promising hydrothermal method for growing well-aligned TiO2 single-crystal NRs that can be employed in solar cell applications.

Effect of GO Additive in ZnO/rGO Nanocomposites with Enhanced Photosensitivity and Photocatalytic Activity.

Zinc oxide/reduced graphene oxide nanocomposites (ZnO/rGO) are synthesized via a simple one-pot solvothermal technique. The nanoparticle-nanorod turnability was achieved with the increase in GO additive, which was necessary to control the defect formation. The optimal defect in ZnO/rGO not only increased ZnO/rGO surface and carrier concentration, but also provided the alternative carrier pathway assisted with rGO sheet for electron-hole separation and prolonging carrier recombination. These properties are ideal for photodetection and photocatalytic applications. For photosensing properties, ZnO/rGO shows the improvement of photosensitivity compared with pristine ZnO from 1.51 (ZnO) to 3.94 (ZnO/rGO (20%)). Additionally, applying bending strain on ZnO/rGO enhances its photosensitivity even further, as high as 124% at r = 12.5 mm, due to improved surface area and induced negative piezoelectric charge from piezoelectric effect. Moreover, the photocatalytic activity with methylene blue (MB) was studied. It was observed that the rate of MB degradation was higher in presence of ZnO/rGO than pristine ZnO. Therefore, ZnO/rGO became a promising materials for different applications.