More than a decade of research in the field of thermal, motion, vibration and electromagnetic radiation energy harvesting has yielded increasing power output and smaller embodiments. Power management circuits for rectification and DC-DC conversion are becoming able to efficiently convert the power from these energy harvesters. This paper summarizes recent energy harvesting results and their power management circuits.

Micropower energy harvesting

Advances in the design and assembly of flexible thermoelectric device

The epitaxial growth of a perovskite matrix on quantum dots (QDs) has enabled the emergence of efficient red light-emitting diodes (LEDs) because it unites efficient charge transport with strong surface passivation. However, the synthesis of wide-band gap (Eg) QD-in-matrix heterostructures has so far remained elusive in the case of sky-blue LEDs. Here, we developed CsPbBr3 QD-in-perovskite matrix solids that enable high luminescent efficiency and spectral stability with an optical Eg of over 2.6 eV. We screened alloy candidates that modulate the perovskite Eg and allow heteroepitaxy, seeking to implement lattice-matched type-I band alignment. Specifically, we introduced a CsPb1-xSrxBr3 matrix, in which alloying with Sr2+ increased the Eg of the perovskite and minimized lattice mismatch. We then developed an approach to passivation that would overcome the hygroscopic nature of Sr2+. We found that bis(4-fluorophenyl)phenylphosphine oxide strongly coordinates with Sr2+ and provides steric hindrance to block H2O, a finding obtained by combining molecular dynamics simulations with experimental results. The resulting QD-in-matrix solids exhibit enhanced air- and photo-stability with efficient charge transport from the matrix to the QDs. LEDs made from this material exhibit an external quantum efficiency of 13.8% and a brightness exceeding 6000 cd m-2.

Wide-Bandgap Perovskite Quantum Dots in Perovskite Matrix for Sky-Blue Light-Emitting Diodes.

Toward next‐generation electroluminescent quantum dot (QD) displays, inkjet printing technique has been convinced as one of the most promising low‐cost and large‐scale manufacturing of patterned quantum dot light‐emitting diodes (QLEDs). The development of high‐quality and stable QD inks is a key step to push this technology toward practical applications. Herein, a universal ternary‐solvent‐ink strategy is proposed for the cesium lead halides (CsPbX3) perovskite QDs and their corresponding inkjet‐printed QLEDs. With this tailor‐made ternary halogen‐free solvent (naphthene, n‐tridecane, and n‐nonane) recipe, a highly dispersive and stable CsPbX3 QD ink is obtained, which exhibits much better printability and film‐forming ability than that of the binary solvent (naphthene and n‐tridecane) system, leading to a much better qualitied perovskite QD thin film. Consequently, a record peak external quantum efficiency (EQE) of 8.54% and maximum luminance of 43 883.39 cd m−2 is achieved in inkjet‐printed green perovskite QLEDs, which is much higher than that of the binary‐solvent‐system‐based devices (EQE = 2.26%). Moreover, the ternary‐solvent‐system exhibits a universal applicability in the inkjet‐printed red and blue perovskite QLEDs as well as cadmium (Cd)‐based QLEDs. This work demonstrates a new strategy for tailor‐making a general ternary‐solvent‐QD‐ink system for efficient inkjet‐printed QLEDs as well as the other solution‐processed electronic devices in the future.

A Universal Ternary‐Solvent‐Ink Strategy toward Efficient Inkjet‐Printed Perovskite Quantum Dot Light‐Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) have received great attention in recent years due to their narrow emission bandwidth and tunable emission spectrum. Efficient red emission is one of most important parts for lighting and displays. Quasi-2D perovskites can deliver high emission efficiency due to the strong carrier confinement, while the external quantum efficiencies (EQE) of red quasi-2D PeLEDs are inefficient at present, which is due to the complex distribution of different n-value phases in quasi-2D perovskite films. In this work, the phase distribution of the quasi-2D perovskite is finely controlled by mixing two different large organic cations, which effectively reduces the amount of smaller n-index phases, meanwhile the passivation of lead and halide defects in perovskite films is realized. Accordingly, the PeLEDs show 25.8% EQE and 1300 cd m−2 maximum brightness at 680 nm, which exhibits the highest performance for red PeLEDs up to now. 

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Red Perovskite Light‐Emitting Diodes with Efficiency Exceeding 25% Realized by Co‐Spacer Cations

Coffee-Stain-Free Perovskite Film for Efficient Printed Light-Emitting Diode

Metal halide perovskite light-emitting diodes (PeLEDs) have been regarded as alternative candidates for full-color display applications with rapid progress to surge the external quantum efficiencies (EQEs) over 20% However, in contrast to the high efficiencies of green, red, and near-infrared PeLEDs, the performance of their blue cousins is still lagging behind, especially the pure-blue one Obtaining blue perovskite films with negligible nonradiative recombination loss and high stability is of great importance to realize efficient and spectrally stable blue PeLEDs In this work, through partially replacing the toxic lead ions (Pb2+) with ecofriendly strontium ions (Sr2+) to tune the emission wavelength along with using passivation strategies, all-inorganic pure-blue perovskite films with a high photoluminescence quantum yield of 607% were achieved, which then delivered PeLEDs with a luminance of 510 cd m-2 and an EQE of 143% The device yields a record radiance among the most efficient PeLEDs at 467 nm In addition, the resultant PeLEDs displayed exceptional spectral stability during the electrical bias operation Our work provides a promising avenue to develop environmentally friendly perovskite materials for efficient and spectrally stable pure-blue PeLEDs and beyond

Efficient and Bright Pure-Blue All-Inorganic Perovskite Light-Emitting Diodes from an Ecofriendly Alloy.

The innate capability of direct heat–electricity conversion endows thermoelectric (TE) materials with great application potential in the fields of low-grade heat harvesting, solid-state cooling, and sensing. Recently, the rapid development of information technology such as the Internet of Things and the popularization of wearable electronic devices have stimulated a period of prosperity for the research on flexible thermoelectric (FTE) devices. At the same time, the research on printed electronics (PEs) is expected to provide scalable and cost-effective manufacturing approaches for FTE devices. This review focuses on the recent progress in printed flexible thermoelectric (PFTE) devices and their applications. At first, the fundamental theories behind TEs and the related performance optimization strategies for FTE devices, as well as the history and applications of PEs, are introduced. Then, the state-of-the-art materials adopted in FTE devices, including materials for TE legs, solvents, dispersants, surfactants, and adhesives for printable inks/pastes, substrates, and electrodes, and the related printing methods are summarized. Subsequently, the applications and device performance of PFTE devices in thermoelectric generators (TEGs), thermoelectric coolers (TECs) and thermoelectric sensors (TESs) over the last decade are reviewed. At last, the challenges existing currently in the PFTE field are discussed and some perspectives on the future investigations toward high-performance, low-cost PFTE devices are proposed.

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Printed flexible thermoelectric materials and devices

Quasi-2D perovskites are enchanting alternative materials for solar cells due to their intrinsic stability. The manipulation of crystal orientation of quasi-2D perovskites is indispensable to target efficient devices, however, the origin of orientation during the film fabrication process still lacks in-depth understanding and convincing evidence yet, which hinders further boosting the performance of photovoltaic devices. Herein, the crystallizing processes during spin-coating and annealing are probed by in situ grazing-incidence wide-angle X-ray scattering (GIWAXS), and the incident-angle-dependent GIWAXS is conducted to unveil the phase distribution in the films. It is found that undesirable lead iodide sol-gel formed intermediate phase would disturb oriented crystalline growth, resulting in random crystal orientation in poor quasi-2D films. A general strategy is developed via simple additive agent incorporation to suppress the formation of the intermediate phase. Accordingly, highly oriented perovskite films with reduced trap density and higher carrier mobility are obtained, which enables the demonstration of optimized quasi-2D perovskite solar cells with a power conversion efficiency of 15.2% as well as improved stability. This work paves a promising way to manipulate the quasi-2D perovskites nucleation and crystallization processes via tuning nucleation stage.

Jiaqing Zang

Papers

Coffee-Stain-Free Perovskite Film for Efficient Printed Light-Emitting Diode

Efficient and Bright Pure-Blue All-Inorganic Perovskite Light-Emitting Diodes from an Ecofriendly Alloy.

Printed flexible thermoelectric materials and devices

Unveiling Crystal Orientation in Quasi-2D Perovskite Films by In Situ GIWAXS for High-Performance Photovoltaics.

Freestanding Silicon Nanowires Mesh for Efficient Electricity Generation from Evaporation-Induced Water Capillary Flow