A photovoltaic device with an efficiency that could break the theoretical limit, exceeding ~60% is the focus in the research field in recent years. The efficiency of three important processes in a ...photovoltaic device need to be ensured to materialize the goal i.e., electron excitations, injections and regenerations. A multiple exciton generation (MEG) mechanism has been proven to increase the photovoltaic conversion efficiency - achievable via usage of small size lead chalcogenides as main light absorber of the photovoltaic device. An efficient electron injection in an excitonic solar cell could be achieved upon fulfilment of the following factors i.e., (i) LUMOfluorophore>CBphotoelectrode, and (ii) small offset between the LUMOfluorophore and CBphotoelectrode. The opto-electronic properties of lead chalcogenide are tuneable based on its size and morphology. Therefore, a synthesis method that could control the size and morphology of the yielded lead chalcogenide plays an important role. This research investigated the effect of additional activated carbon (AC) to the yielded PbS using vacuum thermal evaporator method. The PbS thin films were fabricated with addition of AC with different surface areas i.e., 80 m2/g, 650 m2/g and 1560 m2/g using thermal evaporator at vacuum pressure of 1.0 × 10−5 Torr. The surface area of the ACs was determined using Micromeritics ASAP 2020 BET (Brunauer-Emmett-Teller). The morphology, elemental analysis, crystal structure, opto-electronic, electron injection efficiency and electrical conductivity of the PbS thin film was characterized using Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Spectrometer (EDX), X-Ray Diffractometer (XRD), absorption spectrometer, photoluminescence spectrometer (PL), and Bridge Technology 4-point probes (4PP) respectively. The excited and ground states of the PbS, and redox potential of ionLic PMII electrolyte were determined using quantum chemical calculations at b3lyp/lanl2dz level of theory. Three important observations have been made i.e., (i) addition of AC with the PbS reactants affects the yielded morphology of PbS thin film, (ii) bare PbS/TiO2 device structure offers electron injection efficiency as high as 97% from the PbS to TiO2, and (iii) the bare PbS/TiO2 device structure would offer maximum VOC of ca. 1.7 V, however need to be paired with an electrolyte that possess oxidation potential of ca. −6.5 eV.
•Activated carbon provides alternative heating mechanism that affects the yielded morphology of thin film.•PbS/TiO2-based solar cell offers electron injection efficiency as high as ca. 97%.•Electrolyte with oxidation potential of –6.5 eV would materialize the PbS/TiO2-based solar cell with Voc ca. 1.7 V.
Two-dimensional MoS2 has been speculated to be the best material to replace graphene due to its peculiar structural-electronic properties. The MoS2 with size smaller than its exciton Bohr radius (ca. ...1.61 nm) would favor multi exciton generation upon absorption of photon with sufficient energy, Ephoton ≫ Egap (1.89 eV); which would increase the efficiency of an excitonic solar cell greater than 60%. Despite promising properties of the MoS2, however an excitonic solar cell with high efficiency is yet to be exhibited. In this work, the MoS2 thin films were fabricated using vacuum thermal evaporation technique and characterized. Four objectives have been outlined i.e., to study the effect of heating rate (steady, and rapid) on the (i) morphology, (ii) size, (iii) optoelectronic and (iv) crystal properties of the fabricated thin films. The MoS2 precursor was heated at the rate 2.027 A/s (steady), and 18.75 A/s (rapid), 1.5 × 10−3 Torr, 1.48 A, and 4.58 V. The deposited films later were characterized using Field Emission Scanning Electron Microscope with Energy Dispersive X-ray attachment, photoluminescence spectrometer, UV–vis-NIR spectrometer, and X-ray Diffractometer. The fabricated thin films exhibited nanosphere morphology with different size distributions i.e., wide (steady heating), and narrow (rapid heating). Two hypotheses were made based on the optoelectronic properties i.e., the basic building block of the MoS2 thin film fabricated under steady heating is (i) experiencing stronger quantum confinement effect, and (ii) dominated by nanocrystals which are smaller than that of the rapid heating. Similar energy loss could be expected in both MoS2 thin films i.e., ca. 0.15 to 0.17 eV, indicating the existence of shallow trap states. The MoS2 thin films were dominated by (002), (004), and (106) crystal planes. Therefore, the vacuum thermal evaporation technique would offer materials with unique size, crystal arrangement, and optoelectronic properties upon change of heating rate.
Quantum confined structure-based solar cell is promising two folds increment of the maximum theoretical photovoltaic conversion efficiency i.e., > 60% in comparison with that of the bulk analogs ...e.g., silicon-based and dye sensitized solar cell (ca. 32% of maximum theoretical efficiency). The key to the significant increment is the ability of the fluorophore to exhibit multiple exciton generation upon absorption photon with sufficient energy. Small size of lead chalcogenides (PbS, PbSe, PbTe) crystals have been reported and proven experimentally could exhibit this unique property. We have investigated few clusters of narrow bandgap lead chalcogenides nanocrystals i.e., (PbS)n, (PbSe)n and (PbTe)n; which n = 4 - 80. The cluster models were optimized using quantum chemical calculations to the lowest energy geometry at B3LYP/lanl2dz level of theory. The predicted realistic (PbS)
80
, (PbSe)
50
, and (PbTe)
74
clusters with the size, and bandgap of 4.58 nm (2.00 eV), 4.03 nm (1.51 eV), and 4.84 nm (1.55 eV) are smaller than that of their exciton Bohr radius i.e., 5.01, 13.1, and 24.8 nm respectively. Therefore, the occurrence of multi exciton generation in the clusters is hypothesized upon absorption of photon with E
photon
= 2E
g
.
Electronic learning (e-learning) has become the main method of teaching and learning for many educational institutions during the COVID-19 pandemic. The purpose of this study is to investigate the ...students’ acceptance of e-learning during the COVID-19 pandemic. Quantitative research methods were utilized in order to obtain the necessary data. A total of 100 respondents from three science courses, which were Biology (ED247), Chemistry (ED260), and Physics (ED248) in the Faculty of Education, University Teknologi MARA, Puncak Alam answered a questionnaire given via Google Forms. The IBM SPSS version 25.0 software was used for data analysis. The results show that the students’ acceptance towards e-learning is low based on research question 1 (mean=3.05, SD=.796), research question 2 (mean=1.18, SD=.386), research question 3 (mean=1.18, SD=.435) and research question 4 (mean=1.44, SD=.608). In conclusion, the student’s acceptance of e-learning during the COVID-19 pandemic is significant to improve an educational process by creating and sustaining meaningful learning.
Quantum confined structure-based solar cell is promising two folds increment of the maximum theoretical photovoltaic conversion efficiency i.e., > 60% in comparison with that of the bulk analogs ...e.g., silicon-based and dye sensitized solar cell (ca. 32% of maximum theoretical efficiency). The key to the significant increment is the ability of the fluorophore to exhibit multiple exciton generation upon absorption photon with sufficient energy. Small size of lead chalcogenides (PbS, PbSe, PbTe) crystals have been reported and proven experimentally could exhibit this unique property. We have investigated few clusters of narrow bandgap lead chalcogenides nanocrystals i.e., (PbS)n, (PbSe)n and (PbTe)n; which n = 4 - 80. The cluster models were optimized using quantum chemical calculations to the lowest energy geometry at B3LYP/lanl2dz level of theory. The predicted realistic (PbS)80, (PbSe)50, and (PbTe)74 clusters with the size, and bandgap of 4.58 nm (2.00 eV), 4.03 nm (1.51 eV), and 4.84 nm (1.55 eV) are smaller than that of their exciton Bohr radius i.e., 5.01, 13.1, and 24.8 nm respectively. Therefore, the occurrence of multi exciton generation in the clusters is hypothesized upon absorption of photon with Ephoton = 2Eg.
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