In article number 1700809 by Jung Inn Sohn, SeungNam Cha, and co-workers, flexible quantum dot solar cells mediated by a porous piezoelectric poly(vinylidenefluoride-trifluoroethylene) layer are presented for an advanced energy harvesting technology. An induced piezoelectric potential modulates junction properties of the solar cells, resulting in efficient transport and a reduced non-radiative recombination of photo-generated charge carriers and consequently significant improvements in flexible quantum dot solar cell performances.

Abstract Colloidal quantum dots are promising materials for flexible solar cells, as they have a large absorption coefficient at visible and infrared wavelengths, a band gap that can be tuned across the solar spectrum, and compatibility with solution processing. However, the performance of flexible solar cells can be degraded by the loss of charge carriers due to recombination pathways that exist at a junction interface as well as the strained interface of the semiconducting layers. The modulation of the charge carrier transport by the piezoelectric effect is an effective way of resolving and improving the inherent material and structural defects. By inserting a porous piezoelectric poly(vinylidenefluoride‐trifluoroethylene) layer so as to generate a converging electric field, it is possible to modulate the junction properties and consequently enhance the charge carrier behavior at the junction. This study shows that due to a reduction in the recombination and an improvement in the carrier extraction, a 38% increase in the current density along with a concomitant increase of 37% in the power conversion efficiency of flexible quantum dots solar cells can be achieved by modulating the junction properties using the piezoelectric effect.

A novel synthesis approach for high-quality, large-scale transition-metal dichalcogenide monolayers is developed by SeungNam Cha, Jung Inn Sohn, and co-workers, as described in article number 1702206. The low supersaturation level, triggered by the evaporation of an extremely thin precursor layer, reduces the nucleation density dramatically under a thermodynamically stable environment, yielding uniform and clean large-area monolayer films. The vertically stacked heterostructured device shows a fast response time and a high photoresponsivity.

In article number 1700809 by Jung Inn Sohn, SeungNam Cha, and co-workers, flexible quantum dot solar cells mediated by a porous piezoelectric poly(vinylidenefluoride-trifluoroethylene) layer are presented for an advanced energy harvesting technology. An induced piezoelectric potential modulates junction properties of the solar cells, resulting in efficient transport and a reduced non-radiative recombination of photo-generated charge carriers and consequently significant improvements in flexible quantum dot solar cell performances.

Abstract Colloidal quantum dots are promising materials for flexible solar cells, as they have a large absorption coefficient at visible and infrared wavelengths, a band gap that can be tuned across the solar spectrum, and compatibility with solution processing. However, the performance of flexible solar cells can be degraded by the loss of charge carriers due to recombination pathways that exist at a junction interface as well as the strained interface of the semiconducting layers. The modulation of the charge carrier transport by the piezoelectric effect is an effective way of resolving and improving the inherent material and structural defects. By inserting a porous piezoelectric poly(vinylidenefluoride‐trifluoroethylene) layer so as to generate a converging electric field, it is possible to modulate the junction properties and consequently enhance the charge carrier behavior at the junction. This study shows that due to a reduction in the recombination and an improvement in the carrier extraction, a 38% increase in the current density along with a concomitant increase of 37% in the power conversion efficiency of flexible quantum dots solar cells can be achieved by modulating the junction properties using the piezoelectric effect.

A novel synthesis approach for high-quality, large-scale transition-metal dichalcogenide monolayers is developed by SeungNam Cha, Jung Inn Sohn, and co-workers, as described in article number 1702206. The low supersaturation level, triggered by the evaporation of an extremely thin precursor layer, reduces the nucleation density dramatically under a thermodynamically stable environment, yielding uniform and clean large-area monolayer films. The vertically stacked heterostructured device shows a fast response time and a high photoresponsivity.

Transition metal dichalcogenide (TMDC) monolayers are considered to be potential materials for atomically thin electronics due to their unique electronic and optical properties. However, large-area and uniform growth of TMDC monolayers with large grain sizes is still a considerable challenge. This report presents a simple but effective approach for large-scale and highly crystalline molybdenum disulfide monolayers using a solution-processed precursor deposition. The low supersaturation level, triggered by the evaporation of an extremely thin precursor layer, reduces the nucleation density dramatically under a thermodynamically stable environment, yielding uniform and clean monolayer films and large crystal sizes up to 500 µm. As a result, the photoluminescence exhibits only a small full-width-half-maximum of 48 meV, comparable to that of exfoliated and suspended monolayer crystals. It is confirmed that this growth procedure can be extended to the synthesis of other TMDC monolayers, and robust MoS₂ /WS₂ heterojunction devices are easily prepared using this synthetic procedure due to the large-sized crystals. The heterojunction device shows a fast response time (≈45 ms) and a significantly high photoresponsivity (≈40 AW^-1 ) because of the built-in potential and the majority-carrier transport at the n-n junction. These findings indicate an efficient pathway for the fabrication of high-performance 2D optoelectronic devices.

ABSTRACT In the generation of green hydrogen and oxygen from water, transition metal–based electrode materials have been considered high‐performance water‐splitting catalysts. In water splitting, the oxygen evolution reaction (OER) is the rate‐determining step. To overcome the high overpotential and slow kinetics of OER, the development of effective catalysts to improve electrolysis efficiency is essential. Nickel–iron‐layered double hydroxides (NiFe‐LDHs) have been recognized for their superior electrochemical performance under alkaline OER conditions and have emerged as promising catalysts owing to their unique structure that enhances electrolyte infiltration and exposes more active sites. However, the unique modulation of the crystalline structure of NiFe‐LDHs can further improve OER performance. Accordingly, this study introduces an innovative synthesis approach based on Zn doping and selective Zn etching to increase the ECSA and induce favorable transition‐metal oxidation states in NiFe‐LDHs, thereby improving OER efficiency. After 6 h of Zn etching (Ni 2.9 Zn 0.1 Fe‐6h), the optimized Ni 2.9 Zn 0.1 Fe LDH sample demonstrated remarkable electrochemical performance and stability, requiring small overpotentials of 192 and 260 mV at current densities of 10 and 100 mA cm −2 , respectively. Moreover, the Ni 2.9 Zn 0.1 Fe‐6h electrode could maintain its original overpotential (260 mV) at a current density of 100 mA cm −2 for 250 h. The proposed Zn doping and subsequent partial Zn etching can practically be applied to numerous high‐performance transition metal–based electrochemical catalysts.