Influence of an Sb doping layer in CIGS thin-film solar cells: a photoluminescence study

Sb doping of Cu(In,Ga)Se2 (CIGS) solar cells has been reported to exhibit a positive effect on the morphology of the absorber layer, offering a possibility to lower manufacturing cost by lowering the annealing temperatures during the CIGS deposition. In this work electron microscopy, energy-dispersive x-ray spectroscopy and photoluminescence experiments have been performed on cells deposited on soda-lime glass substrates, adding a thin Sb layer onto the Mo back contact prior to the CIGS absorber deposition. The defect structure of CIGS solar cells doped with Sb in this way has been investigated and is compared with that of undoped reference cells. The influence of substrate temperature during absorber growth has also been evaluated. For all samples the photoluminescence results can be explained by considering three donor–acceptor pair recombination processes involving the same defect pairs

Electronic defect study on low temperature processed Cu(In,Ga)Se2 thin-film solar cells and the influence of an Sb layer

A way to lower the manufacturing cost of Cu(In,Ga)Se-2 (CIGS) thin-film solar cells is to use flexible polymer substrates instead of rigid glass. Because such substrates require lower temperature during absorber deposition, the grain growth of the absorber layer can be hindered which leads to a lower cell performance. Partial compensation of this efficiency loss might be accomplished by growing the absorber in the presence of Sb, which is reported to promote grain growth. In this work CIGS solar cells, deposited on glass substrates, at a reduced substrate temperature with a thin Sb layer (7, 12 nm) on top of the Mo contact are investigated. The diffusion profile of Sb is measured with plasma profiling time of flight mass spectrometry. The beneficial effect of Sb on efficiency and grain size is shown in quantum efficiency measurements and with scanning electron microscopy, respectively. Electric spectroscopy is used to explore the possible effects on the defect structure, more in particular on the dominant shallow acceptor. Admittance spectra exhibit a capacitance step to the geometric capacitance plateau at low temperature (5-60 K). Analyzing this capacitance step, we obtained a good estimate of the activation energy of the intrinsic defects that provide the p-type conductivity of the CIGS absorber. The measurements did not show a change in the nature of the dominant acceptor upon Sb treatment

Switching behaviors of graphene-boron nitride nanotube heterojunctions

High electron mobility of graphene has enabled their application in high-frequency analogue devices but their gapless nature has hindered their use in digital switches. In contrast, the structural analogous, h-BN sheets and BN nanotubes (BNNTs) are wide band gap insulators. Here we show that the growth of electrically insulating BNNTs on graphene can enable the use of graphene as effective digital switches. These graphene-BNNT heterojunctions were characterized at room temperature by four-probe scanning tunneling microscopy (4-probe STM) under real-time monitoring of scanning electron microscopy (SEM). A switching ratio as high as 105 at a turn-on voltage as low as 0.5 V were recorded. Simulation by density functional theory (DFT) suggests that mismatch of the density of states (DOS) is responsible for these novel switching behaviors

Zn-Co metal organic frameworks coated with chitosand and Au nanoparticles for chemo-photothermal-targeted combination therapy of liver cancer

The toxic effects of chemotherapy drugs on normal tissues are still a major limiting factor in cancer treatment. In this paper, we report a metal-organic framework (Zn-Co ZIF) with chitosan-coated outer layer as a carrier for the drug adriamycin hydrochloride (DOX), a treatment for liver cancer, as a novel anti-cancer nanodrug-enhanced carrier. Gold nanoparticles, a good photothermal conversion agent, were combined with the target SH-RGD during surface functionalisation to prepare Zn-Co ZIF@DOX-CS-Au-RGD (ZD-CAR), a nanoplatform with good photothermal conversion properties and targeting for combined liver cancer therapy. ZD-CAR was developed after RGD accurately targeted the tumour and entered the tumour microenvironment (TME), it cleaves and releases the liver cancer therapeutic agent (DOX) in a weak acidic environment to effectively kill tumour cells. The metal skeleton cleavage releases Co2+, which catalyzes the production of oxygen from H2O2 to alleviate the tumour hypoxic environment. The dissolved oxygen could reach 14 mg/L after adding 80 mg/mL of ZD-CAR. Meanwhile, gold nanoparticles could convert light energy into heat energy under 808 NIR irradiation to induce local superheating and kill tumour cells. In summary, this study developed a nanoplatform that combines chemo-photothermal-targeted therapy. It has shown good therapeutic effeciency in cellular experiments and performance tests and has promising applications in anti-cancer therapy

Analysis of the voltage losses in CZTSSe solar cells of varying Sn content

The performance of kesterite (Cu2ZnSn(S,Se)4, CZTSSe) solar cells is hindered by low open circuit voltage (Voc). The commonly used metric for Voc-deficit, namely, the difference between the absorber band gap and qVoc, is not well-defined for compositionally complex absorbers like kesterite where the bandgap is hard to determine. Here, nonradiative voltage losses are analyzed by measuring the radiative limit of Voc, using external quantum efficiency (EQE) and electroluminescence (EL) spectra, without relying on precise knowledge of the bandgap. The method is applied to a series of Cu2ZnSn(S,Se)4 devices with Sn content variation from 27.6 to 32.9 at. % and a corresponding Voc range from 423 to 465 mV. Surprisingly, the lowest nonradiative loss, and hence the highest external luminescence efficiency (QELED), were obtained for the device with the lowest Voc. The trend is assigned to better interface quality between absorber and CdS buffer layer at lower Sn content

Regulation of sensory nerve conduction velocity (SCV) of human bodies responding to annual temperature variations in natural environments

The extensive research interests in environmental temperature can be linked to human productivity/performance as well as comfort and health; while the mechanisms of physiological indices responding to temperature variations remain incompletely understood. This study adopted a physiological sensory nerve conduction velocity (SCV) as a temperature-sensitive biomarker to explore the thermoregulatory mechanisms of human responding to annual temperatures. The measurements of subjects’ SCV (over 600 samples) were conducted in a naturally ventilated environment over all four seasons. The results showed a positive correlation between SCV and annual temperatures and a Boltzmann model was adopted to depict the S-shaped trend of SCV with operative temperatures from 5 °C to 40 °C. The SCV increased linearly with operative temperatures from 14.28 °C to 20.5 °C and responded sensitively for 10.19 °C - 24.59 °C, while tended to be stable beyond that. The subjects’ thermal sensations were linearly related to SCV, elaborating the relation between human physiological regulations and subjective thermal perception variations. The findings reveal the body SCV regulatory characteristics in different operative temperature intervals, thereby giving a deeper insight into human autonomic thermoregulation and benefiting for built environment designs, meantime minimizing the temperature-invoked risks to human health and well-being

Band gap widening at random CIGS grain boundary detected by valence electron energy loss spectroscopy

Cu(In,Ga) Se₂ (CIGS) thin film solar cells have demonstrated very high efficiencies, but still the role of nanoscale inhomogeneities in CIGS and their impact on the solar cell performance are not yet clearly understood. Due to the polycrystalline structure of CIGS, grain boundaries are very common structural defects that are also accompanied by compositional variations. In this work, we apply valence electron energy loss spectroscopy in scanning transmission electron microscopy to study the local band gap energy at a grain boundary in the CIGS absorber layer. Based on this example, we demonstrate the capabilities of a 2nd generation monochromator that provides a very high energy resolution and allows for directly relating the chemical composition and the band gap energy across the grain boundary. A band gap widening of about 20 meV is observed at the grain boundary. Furthermore, the compositional analysis by core-loss EELS reveals an enrichment of In together with a Cu, Ga and Se depletion at the same area. The experimentally obtained results can therefore be well explained by the presence of a valence band barrier at the grain boundary

An Exome-Wide Sequencing Study of Lipid Response to High-Fat Meal and Fenofibrate in Caucasians from the GOLDN Cohort

Our understanding of genetic influences on the response of lipids to specific interventions is limited. In this study, we sought to elucidate effects of rare genetic variants on lipid response to a high-fat meal challenge and fenofibrate (FFB) therapy in the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN) cohort using an exome-wide sequencing-based association study. Our results showed that the rare coding variants in ITGA7, SIPA1L2, and CEP72 are significantly associated with fasting LDL cholesterol response to FFB (P = 1.24E-07), triglyceride postprandial area under the increase (AUI) (P = 2.31E-06), and triglyceride postprandial AUI response to FFB (P = 1.88E-06), respectively. We sought to replicate the association for SIPA1L2 in the Heredity and Phenotype Intervention (HAPI) Heart Study, which included a high-fat meal challenge but not FFB treatment. The associated rare variants in GOLDN were not observed in the HAPI Heart study, and thus the gene-based result was not replicated. For functional validation, we found that gene transcript level of SIPA1L2 is associated with triglyceride postprandial AUI (P \u3c 0.05) in GOLDN. Our study suggests unique genetic mechanisms contributing to the lipid response to the high-fat meal challenge and FFB therapy