Touchpoint-Tailored Ultrasensitive Piezoresistive Pressure Sensors with a Broad Dynamic Response Range and Low Detection Limit.

Wearable pressure sensors with high sensitivity, broad dynamic response range, and low detection limit are highly desirable to enable the applications in electronic skins and soft robotics. In this work, we report a high-performance wearable pressure sensor based on microstructured polydimethylsiloxane (PDMS)/Ag and rough polyimide/Au interdigital electrodes. By tailoring the touchpoints, the resulting pressure sensors show ultrahigh sensitivity (259.32 kPa-1 in the range of 0-2.5 kPa), broad dynamic response range (0-54 kPa), fast response (∼200 µs), and low detection limit (0.36 Pa). Furthermore, the effect of different sensor structural configurations, PDMS geometrical feature, and Ag thickness on the performance of the pressure sensors are systematically investigated. Thanks to these merits, the fabricated pressure sensor is capable of real-time monitoring pulse wave and can act as artificial skin for robot hand to detect weak pressure changes, leading to the great application promise in the fields of biomedical, real-time health monitoring, and intelligent robot.

Lattice Dynamics and Thermal Stability of Cubic-Phase CsPbI3 Quantum Dots.

Cubic-phase CsPbI3 quantum dots (QDs) have been recently synthesized with merits of excellent optoelectronic performance. However, vital properties of cubic CsPbI3 including lattice dynamics and stability at high temperature remain poorly explored. We fabricate cubic CsPbI3 QDs and study their lattice dynamic and thermal stability to 700 K. We obtain Raman modes of cubic CsPbI3 QDs from 300 to 500 K at ultra-low-frequency range down to 15 cm-1, consistent with first-principles calculations. Above 550 K, the modification of Raman features suggests sample degradation. Consistently, temperature-dependent photoluminescence measurements indicate the absence of other luminescence phases up to 700 K. With increasing temperature, the CsPbI3 QD photoluminescence peak has a blue shift with exponentially decreasing intensity, showing faster electronic degradation than structural degradation. Our work provides detailed investigation of CsPbI3 QD lattice dynamics, band gap, and their high-temperature behavior, potentially useful for their emerging optoelectronic applications.

Highly efficient graphene-based Cu(In, Ga)Se2 solar cells with large active area.

Two-dimensional graphene has tremendous potential to be used as a transparent conducting electrode (TCE), owing to its high transparency and conductivity. To date graphene films have been applied to several kinds of solar cells except the Cu(In, Ga)Se2 (CIGS) solar cell. In this work, we present a novel TCE structure consisting of a doped graphene film and a thin layer of poly(methyl methacrylate) (PMMA) to replace the ZnO:Al (AZO) electrode for CIGS. By optimizing the contact between graphene and intrinsic ZnO (i-ZnO), a high power conversion efficiency (PCE) of 13.5% has been achieved, which is among the highest efficiencies of graphene-based solar cells ever reported and approaching those of AZO-based solar cells. Besides, the active area of our solar cells reaches 45 mm(2), much larger than other highly efficient graphene-based solar cells (>10%) reported so far. Moreover, compared with AZO-based CIGS solar cells, the total reflectance of the graphene-based CIGS solar cells is decreased and the quantum efficiency of the graphene-based CIGS is enhanced in the near infrared region (NIR), which strongly support graphene as a competitive candidate material for the TCE in the CIGS solar cell. Furthermore, the graphene/PMMA film can protect the solar cell from moisture, making the graphene-based solar cells much more stable than the AZO-based solar cells.