RESUMO
Owing to the high charge mobility and low processing temperature, ZnO is regarded as an ideal candidate for electron transport layer (ETL) material in thin-film solar cells. For the film preparation, the presently dominated sol-gel (SG) and hydrolysis-condensation (HC) methods show great potential; however, the effect of these two methods on the performance of the resulting devices has not been investigated in the same frame. In this study, the ZnO films made through SG and HC methods were applied in perovskite solar cells (Pero-SCs), and the performances of corresponding devices were compared under parallel conditions. We found that the surface morphologies and the conductivities of the films prepared by SG and HC methods showed great differences. The HC-ZnO films with higher conductivity led to relatively higher device performance, and the best power conversion efficiencie (PCE) of 12.9% was obtained; meanwhile, for Pero-SCs based on SG-ZnO, the best PCE achieved was 10.9%. The better device performance of Pero-SCs based on HC-ZnO should be attributed to the better charge extraction and transportation ability of HC-ZnO film. Moreover, to further enhance the performance of Pero-SCs, a thin layer of pristine C60 was introduced between HC-ZnO and perovskite layers. By doing so, the quality of perovskite films was improved, and the PCE was elevated to 14.1%. The preparation of HC-ZnO film involves relatively lower-temperature (maximum 100 °C) processing; the films showed better charge extraction and transportation properties and can be a more promising ETL material in Pero-SCs.
RESUMO
A long-term mining activity of Jinding Pb-Zn mine area in Yunnan has caused the serious cadmium pollution to the river sediments of the ambient area. The Cd contents of Beidagou river sediments (mean value <10 mg x kg(-1)) are lower than those of Nandagou river sediments (mean value = 266 mg x kg(-1)). The Cd contents of river sediments in different section of Bijiang river occur distinct difference. The Cd contents are rather lower in upstream sediments of Bijiang river, and increase substantially along downstream contaminated section of Bijiang river. The Cd pollution coefficient is higher (R = 21.9-45.2) than Zn (R = 4.9-9.7) and Pb (R = 2.7-4.6). The degree of pollution is estimated by the geoaccumulation index, which indicates the following rank of pollution elements: Cd > Zn > Pb. The river sediments are extremely contaminated in Nandagou river and downstream section of Bijiang river from Nandagou, strongly contaminated in most part of Beidagou river, moderately to strongly contaminated in few river section of Nandagou river, uncontaminated or moderately contaminated in upstream of Bijiang river from Jinding. The heavy metals pollution of river sediments presents increasing trend from Nandagou outlet to Wenzhuang section of Bijiang river.