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Herein, we demonstrate that two-dimensional (2D) CdSeS quantum dot monolayers (QDM) can strongly influence efficient charge transport and charge separation, improving the performance of inverted polymer solar cells (iPSCs). Also, for the first time we report the electronic band structure of CdSeS and CdSeS@ZnS QDs and an effective approach to apply the 2D QDM as an effective electron transport layer in iPSCs from work function studies. The iPSCs with the 2D CdSeS QDM showed maximum power conversion efficiencies of 8.83%, which were 26% higher than the reference. Ultraviolet photoelectron spectroscopy and time-correlated single photon counting (TCSPC) measurements were performed to confirm the charge separation and electron transport behavior in the iPSCs with 2D QDMs. The PL decay time of the iPSCs with the CdSeS QDM at 720 nm was ∼60 ps, which is much faster than that of the iPSCs without the 2D QDM. The enhanced photovoltaic performance of the iPSCs with the 2D CdSeS QDM can be attributed to the effective charge separation and electron transport performance due to the high built-in voltage and fast exciton decay time from the 2D QDM. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2) has been extensively used as a hole transport layer in many inverted polymer solar cell devices. However, its potential as an electron transport layer in a solar cell device has rarely been reported. In this paper, we demonstrate an iPSC with enhanced photovoltaic performance by the introduction of a MoS2 nanosheet (NS) interlayer. Herein, MoS2 NS thin films were uniformly deposited on a polyethylenimine ethoxylated polymer by an electrostatic interaction. The MoS2 NS interlayer in the iPSC device plays important roles as a sub-photo sensitizer and an electron transport layer and provides effective charge separation for the enhancement of device performance. iPSCs with MoS2 NSs based on bulk heterojunction active materials such as P3HT:PC60BM, PTB7:PC71BM and PTB7-Th:PC71BM showed maximum power conversion efficiencies of 3.54%, 8.12%, and 9.08%, respectively, which were 27%, 11%, and 15% higher than those of the reference, respectively. Furthermore, the enhanced photovoltaic performance and electron transport mechanism of the iPSCs with the MoS2 NSs were confirmed experimentally using finite-difference-time-domain modeling and time-correlated single photon counting (TCSPC) measurements. The computational simulation results showed that the light absorption of the iPSCs with the MoS2 NS interlayer was slightly better than that of the iPSCs without the MoS2 NS interlayer. The electron decay time of PTB7:PC71BM with the MoS2 NS interlayer at a wavelength of 700 nm was reduced to 60 ps from 100 ps of PTB7:PC71BM without the MoS2 NS interlayer. The efficient light absorption and electron transfer characteristics of MoS2 NSs significantly improved the photovoltaic conversion performance of the iPSC devices. [ABSTRACT FROM AUTHOR]

We report highly sensitive, tunable, and durable strain sensors based on a simple structure consisting of a multilayered film of gold (Au) nanosheets as a sensing layer on a highly stretchable Ecoflex substrate. The high sensitivity of the sensor at different levels of strain was achieved by controlling the stacking number of micrometer-sized Au nanosheets with a thickness of ∼20 nm, which enabled the control of piezoresisitivity of the sensing layer through the change in contact resistance between Au nanosheets under mechanical bending and stretching. The Au nanosheet-based strain sensors exhibited excellent electrical stability without degradation in sensing-performance even after 10 000 stretching cycles. Our highly sensitive, reproducible, tunable, and durable strain sensors were demonstrated to monitor large-scale body motions such as bending, walking, jumping, and squatting, as well as to detect small skin strains induced by minute movements of muscles upon breathing, speaking, and coughing. [ABSTRACT FROM AUTHOR]