Yiping Zhang

Light-emitting diodes (LEDs) are essential for future energy-saving lighting and display technology owing to their high efficiency, long lifetime, and low cost. To further enhance the performance of GaN-based LEDs, electroluminescent (EL) cooling has been widely predicted to be useful over the past several decades; however, it has not been experimentally achieved. Herein, thermoelectric and phonon-pumped GaN-based LEDs have been demonstrated by both experimental measurements and theoretical modeling. It is surprisingly found that the effect of increasing temperature changes from negative to positive when the operating point is moved to the high-efficiency, midvoltage range. The power efficiency exhibits a maximum 2.24-fold improvement with increasing temperature (from room temperature to 473 K), and the peak efficiency at all elevated temperatures outperforms that at room temperature, where the Peltier effect changes from Peltier heat to Peltier cooling. Under lower biases, the phonon-assisted Peltier cooling provides additional energy for carriers to overcome the potential barrier and achieve recombination. The findings not only give an insightful understanding of EL cooling but also provide guidelines on thermal management and designing high-performance GaN-based LED devices and arrays (e.g., micro-LEDs), which can be further extended to other kinds of LEDs and optoelectronic devices.

Phototransistors have great application prospects in automotive vehicle, smart home, healthcare, imaging, and display. However, so far, there has been no report of flexible phototransistors that simultaneously achieve both high mobility and detectivity. Additionally, phototransistors are conventionally relied on thick channel layers and previous thin channel layers based devices only show poor performance. Here, we report flexible phototransistors based on ultrathin niobium-doped indium oxide (InNbO, 5 nm)/indium tin oxide (ITO, 3 nm) channel layers, which possess high mobility (49.21 cm2 V−1 s−1) and high detectivity (3.02 × 1014 Jones) simultaneously. Significantly, the devices offer a broad spectral responsivity (from violet to green emissions). We postulate that the high mobility can be ascribed to the diffusion of Sn atoms (from ITO) and conduction band offset (between InNbO and ITO), while the high detectivity originates from the low dark current. To illustrate the capabilities of flexible phototransistors, we demonstrate both a flexible active-matrix organic light-emitting diode display pixel circuit and an imaging system. Our approach unlocks new possibilities to achieve flexible phototransistors with superior performance, which suggest a great potential in next-generation flexible, stretchable, bendable, and low-cost electronics.