Solution processed infrared- and thermo-photovoltaics based on 0.7 eV bandgap PbS colloidal quantum dots.

Harnessing low energy photons is of paramount importance for multi-junction high efficiency solar cells as well as for thermo-photovoltaic applications. However, semiconductor absorbers with the bandgap lower than 0.8 eV have been limited to III-V (InGaAs) or IV (Ge) semiconductors that are characterized by high manufacturing costs and complicated lattice matching requirements in their growth and integration with higher bandgap cells. Here, we have developed solution processed low bandgap photovoltaic devices based on PbS colloidal quantum dots (CQDs) with a bandgap of 0.7 eV suited for both thermo-photovoltaics and low energy solar photon harvesting. By matching the spectral response of those cells to that of the infrared solar spectrum, we report a record high short circuit current (JSC) of 37 mA cm-2 under the full solar spectrum and 5.5 mA cm-2 when placed at the back of a silicon wafer resulting in power conversion efficiencies (PCEs) of 6.4% and 0.7%, respectively. Moreover, the device reached an above bandgap PCE of ∼6% as a thermo-photovoltaic cell recorded under a 1000 °C blackbody radiator.

Capacitive behavior of carbon nanotube thin film induced by deformed ZnO microspheres.

Multiwalled carbon nanotubes (CNTs) are uniformly distributed with piezoelectric microspheres. This leads to a large strain gradient due to an induced capacitive response, providing a 250% enhancement in electromechanical response compared with pristine CNTs. The fabricated large-area flexible thin film exhibits excellent pressure sensitivity, which can even detect an arterial pulse with a much faster response time (∼79 ms) in a bendable configuration. In addition, the film shows a rapid relaxation time (∼0.4 s), high stability and excellent durability with a rapid loading-unloading cycle. The dominant contribution of piezoelectric microspheres in a CNT matrix as opposed to nanoparticles showed a much higher sensitivity due to the large change in capacitance. Therefore, hybrid microstructures have various potential applications in wearable smart electronics, including detection of human motion and wrist pulses.

Surface photo-charge effect in doped-ZnO nanorods for high-performance self-powered ultraviolet photodetectors.

The unique photo-charge characteristics of chlorine-doped zinc oxide nanorods (Cl-ZnO NRs) are explored for the first time in ultraviolet (UV) photodetector (PD) that offers an outstanding self-powered photoresponse towards low UV illumination signals. A self-powered Cl-ZnO NRs PD exhibits superior photon detection speed of the order of a few ms with high sensitivity and photoelasticity. Therefore, the presented PD opens up a novel route to fabricate highly efficient self-powered PDs on a large scale without employing complex multilayer systems.