Monolayer molybdenum disulfide (MoS 2 ) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS 2 devices. Here, highly crystalline molybdenum diselenide (MoSe 2 ) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS 2 and MoSe 2 monolayers reveals that the MoSe 2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe 2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS 2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS 2 . This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe 2 and MoS 2 and is useful for guiding future designs in 2D material-based optoelectronic devices.

Interface carrier recombination currently hinders the performance of hybrid organic-silicon heterojunction solar cells for high-efficiency low-cost photovoltaics. Here, we introduce an intermediate 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) layer into hybrid heterojunction solar cells based on silicon nanowires (SiNWs) and conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS). The highest power conversion efficiency reaches a record 13.01%, which is largely ascribed to the modified organic surface morphology and suppressed saturation current that boost the open-circuit voltage and fill factor. We show that the insertion of TAPC increases the minority carrier lifetime because of an energy offset at the heterojunction interface. Furthermore, X-ray photoemission spectroscopy reveals that TAPC can effectively block the strong oxidation reaction occurring between PEDOT:PSS and silicon, which improves the device characteristics and assurances for reliability. These learnings point toward future directions for versatile interface engineering techniques for the attainment of highly efficient hybrid photovoltaics.

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Foundry-based routes to transient silicon electronic devices have the potential to serve as the manufacturing basis for "green" electronic devices, biodegradable implants, hardware secure data storage systems, and unrecoverable remote devices. This article introduces materials and processing approaches that enable state-of-theart silicon complementary metal-oxide-semiconductor (CMOS) foundries to be leveraged for high-performance, water-soluble forms of electronics. The key elements are (i) collections of biodegradable electronic materials (e.g., silicon, tungsten, silicon nitride, silicon dioxide) and device architectures that are compatible with manufacturing procedures currently used in the integrated circuit industry, (ii) release schemes and transfer printing methods for integration of multiple ultrathin components formed in this way onto biodegradable polymer substrates, and (iii) planarization and metallization techniques to yield interconnected and fully functional systems. Various CMOS devices and circuit elements created in this fashion and detailed measurements of their electrical characteristics highlight the capabilities. Accelerated dissolution studies in aqueous environments reveal the chemical kinetics associated with the underlying transient behaviors. The results demonstrate the technical feasibility for using foundry-based routes to sophisticated forms of transient electronic devices, with functional capabilities and cost structures that could support diverse applications in the biomedical, military, industrial, and consumer industries.soft electronics | biodegradable electronics | transfer printing | undercut etching | hydrolysis S emiconductor technology is increasingly essential to nearly all aspects of modern society, with projections of market sizes that will exceed $7 trillion in 2017, equivalent to 10% of the world's gross domestic product (1-4). The rapid and accelerating pace of innovation in this area leads to increases in the frequency with which consumers upgrade their devices, thereby contributing to the production of >50 million tons of electronic waste (e-waste) each year (5, 6). Furthermore, the anticipated emergence of electronics for internet-of-things applications, along with the continued proliferation of radio frequency (RF) identification tags and other high-volume electronic goods, create daunting challenges with the management of this e-waste (7, 8). These considerations motivate research into forms of electronics that can degrade naturally into the environment to harmless end products. Such technology is also of interest for other, unique classes of applications, ranging from biodegradable, temporary electronic implants to hardware secure data systems and unrecoverable, field-deployed devices (9-12). Sometimes referred to collectively as transient electronics, these types of devices can be constructed by using designer materials, such as specially formulated polymers or natural products (13-16), or clever combinations of established materials, well-aligned to existing ...

Transient forms of electronics, systems that disintegrate, dissolve, resorb, or sublime in a controlled manner after a well‐defined operating lifetime, are of interest for applications in hardware secure technologies, temporary biomedical implants, “green” consumer devices and other areas that cannot be addressed with conventional approaches. Broad sets of materials now exist for a range of transient electronic components, including transistors, diodes, antennas, sensors, and even batteries. This work reports the first examples of transient light‐emitting diodes (LEDs) that can completely dissolve in aqueous solutions to biologically and environmentally benign end products. Thin films of highly textured ZnO and polycrystalline Mo serve as semiconductors for light generation and conductors for transparent electrodes, respectively. The emitted light spans a range of visible wavelengths, where nanomembranes of monocrystalline silicon can serve as transient filters to yield red, green, and blue LEDs. Detailed characterization of the material chemistries and morphologies of the constituent layers, assessments of their performance properties, and studies of their dissolution processes define the underlying aspects. These results establish an electroluminescent light source technology for unique classes of optoelectronic systems that vanish into benign forms when exposed to aqueous conditions in the environment or in living organisms.