CuS nanoplate films were synthesized on FTO conducting glass substrates via a facile microwave-assisted hydrothermal (MHT) route and applied directly as a low-cost and high-efficiency counter electrode (CE) for liquid-junction quantum dot-sensitized solar cells (QDSSC). The two-dimensional structure of nanoplate provide high surface area for more active catalytic sites and easy accessibility for polysulfide electrolyte, which leads to the remarkable decrease in charge transfer resistance and the enhancement of catalytic activity of CE. As a result, the liquid-junction QDSSC assembled with the prepared CuS-2 CE achieves maximum power conversion efficiency (PCE) of 4.97%, which is superior than that of CuS fabricated by conventional chemical bath deposition method based cell (PCE 4.06%) and the 100 nm thin sputtered Pt/FTO CE based cell (PCE 3.08%). Furthermore, the prepared CuS exhibits highly chemical stability in polysulfide electrolyte, resulting in reproducible performance. These results show the potential application of MHT synthetic method in preparing metal chalcogenide CE for high-performance liquid-junction QDSSC in the future.

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This paper studies elastic–plastic contact between Greenwood–Williamson (GW) rough surfaces, on which there are many asperities with the same radius whose height obeys the Gaussian distribution. A new plasticity index is defined as the ratio of the standard deviation of the height of asperities on the rough surface to the single-asperity critical displacement (the transition point from the elastic to the elastic-fully plastic deformation regime), which is linearly proportional to the GW plasticity index to the power of 2. The equations for the load/area–separation relationship of rough surfaces are presented based on Wang and Wang's smooth model of singe-asperity elastic–plastic contact, which is an improvement of the Kogut–Etsion (KE) empirical model based on finite element analysis (FEA) data. The load/area–separation relationship can be described by empirical Gaussian functions. The load–area relationship of rough surfaces is approximately linear. The average pressure is only function of the new plasticity index. According to Wang and Wang's conclusion that Etsion et al. single-asperity elastic–plastic loading (EPL) index is approximately equal to the ratio of the single-asperity residual plastic contact displacement to the single-asperity total elastic–plastic contact displacement, the equations for the relationship between Kadin et al. modified plasticity index (MPI) and separation of rough surfaces are also presented. In addition, the MPI is approximately linearly proportional to the separation between rough surfaces for a given new plasticity index ranging from 5 to 30. When the new plasticity index is smaller than 5, due to the large proportion of the elastic deformation in the total deformation, the MPI slightly deviate from linearity.

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