RESUMEN
Interface engineering has led to significant progress in solution-processed CdTe nanocrystal (NC) solar cells in recent years. High performance solar cells can be fabricated by introducing a hole transfer layer (HTL) between CdTe and a back contact electrode to reduce carrier recombination by forming interfacial dipole effect at the interface. Here, we report the usage of a commercial product 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro) as a hole transfer layer to facilitate the hole collecting for CdTe nanocrystal solar cells. It is found that heat treatment on the hole transfer layer has significant influence on the NC solar cells performance. The Jsc, Voc, and power conversion efficiency (PCE) of NC solar cells are simultaneously increased due to the decreased contact resistance and enhanced built-in electric field. We demonstrate solar cells that achieve a high PCE of 8.34% for solution-processed CdTe NC solar cells with an inverted structure by further optimizing the HTL annealing temperature, which is among the highest value in CdTe NC solar cells with the inverted structure.
RESUMEN
CdTe nanocrystal (NC) solar cells have received much attention in recent years due to their low cost and environmentally friendly fabrication process. Nowadays, the back contact is still the key issue for further improving device performance. It is well known that, in the case of CdTe thin-film solar cells prepared with the close-spaced sublimation (CSS) method, Cu-doped CdTe can drastically decrease the series resistance of CdTe solar cells and result in high device performance. However, there are still few reports on solution-processed CdTe NC solar cells with Cu-doped back contact. In this work, ZnTe:Cu or Cu:Au back contact layer (buffer layer) was deposited on the CdTe NC thin film by thermal evaporation and devices with inverted structure of ITO/ZnO/CdSe/CdTe/ZnTe:Cu (or Cu)/Au were fabricated and investigated. It was found that, comparing to an Au or Cu:Au device, the incorporation of ZnTe:Cu as a back contact layer can improve the open circuit voltage (Voc) and fill factor (FF) due to an optimized band alignment, which results in enhanced power conversion efficiency (PCE). By carefully optimizing the treatment of the ZnTe:Cu film (altering the film thickness and annealing temperature), an excellent PCE of 6.38% was obtained, which showed a 21.06% improvement compared with a device without ZnTe:Cu layer (with a device structure of ITO/ZnO/CdSe/CdTe/Au).
RESUMEN
Nanocrystal solar cells (NCs) allow for large scale solution processing under ambient conditions, permitting a promising approach for low-cost photovoltaic products. Although an up to 10% power conversion efficiency (PCE) has been realized with the development of device fabrication technologies, the open circuit voltage (Voc) of CdTe NC solar cells has stagnated below 0.7 V, which is significantly lower than most CdTe thin film solar cells fabricated by vacuum technology (around 0.8 V~0.9 V). To further improve the NC solar cells' performance, an enhancement in the Voc towards 0.8â»1.0 V is urgently required. Given the unique processing technologies and physical properties in CdTe NC, the design of an optimized band alignment and improved junction quality are important issues to obtain efficient solar cells coupled with high Voc. In this work, an efficient method was developed to improve the performance and Voc of solution-processed CdTe nanocrystal/TiO2 hetero-junction solar cells. A thin layer of solution-processed CdS NC film (~5 nm) as introduced into CdTe NC/TiO2 to construct hetero-junction solar cells with an optimized band alignment and p-n junction quality, which resulted in a low dark current density and reduced carrier recombination. As a result, devices with improved performance (5.16% compared to 2.63% for the control device) and a Voc as high as 0.83 V were obtained; this Voc value is a record for a solution-processed CdTe NC solar cell.
RESUMEN
CONTEXT: Oleanolic acid (OA), a triterpenoid compound, exists in many plants. It has numerous bioactivities and has been used to treat hepatitis in China. However, few studies have reported its effect on the central nervous system, especially in ischemic stroke. OBJECTIVE: To explore the protective effects of OA on cerebral ischemic injury for the first time. MATERIALS AND METHODS: Survival time was tested in mice injured by bilateral common carotid artery ligation (BCCAL). Neurological function, infarct area, cerebral edema, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) were estimated in rats operated by middle cerebral artery occlusion (MCAO). Cell survival, lactate dehydrogenase (LDH), SOD, reduced glutathione (GSH), MDA, mitochondrial membrane potential (MMP) and succinic dehydrogenase (SDH) were detected in H(2)O(2)-injured PC12 cells. RESULTS: Pre-administration with OA significantly prolonged survival time in mice at 50 and 25 mg/kg, alleviated neurological function, infarct area and cerebral edema, increased SOD and GSH-Px activities and decreased MDA level in rats at 25 and 12.5 mg/kg. Pre-treatment with OA at 10 and 1 µM remarkably improved cell survival, enhanced SOD activity and GSH content, reduced LDH and MDA levels and reversed the lowering of MMP and SDH activity. DISCUSSION AND CONCLUSION: These results demonstrate that oleanolic acid effectively alleviates cerebral ischemic damage in vivo and oxidative injury in vitro, which may be in part due to the modulation of endogenous antioxidants and the improvement of mitochondrial function. Oleanolic acid may be a potential medicine for attenuating ischemic stroke.
