Flexible electronics based on one-dimensional inorganic semiconductor nanowires and two-dimensional transition metal dichalcogenides

Flexible electronics technology is considered as a revolutionary technology to unlock the bottleneck of traditional rigid electronics that prevalent for decades,thereby fueling the next-generation electronics.In the past few decades,the research on flexible electronic devices based on organic materials has witnessed rapid development and substantial achievements,and inorganic semiconductors are also now beginning to shine in the field of flexible electronics.As validated by the latest research,some of the inorganic semiconductors,particularly those at low dimension,unexpectedly exhibited excellent mechanical flexibility on top of superior electrical properties.Herein,we bring together a comprehensive analysis on the recently burgeoning low-dimension inorganic semiconductor materials in flexible electronics,including one-dimensional(1D)inorganic semiconductor nanowires(NWs)and two-dimensional(2D)transition metal dichalcogenides(TMDs).The fundamental electrical properties,optical properties,mechanical properties and strain engineering of materials,and their performance in flexible device applications are discussed in detail.We also propose current challenges and predict future development directions including material synthesis and device fabrication and integration.

Room-temperature plastic inorganic semiconductors for flexible and deformable electronics

Flexible electronics ushers in a revolution to the electronics industry in the 21st century.Ideally,all components of a flexible electronic device including the functional component shall comply with the deformation to ensure the structural and functional integrity,imposing a pressing need for developing roomtemperature strain-tolerant semiconductors.To this end,there is a long-standing material dilemma:inorganic semiconductors are typically brittle at room temperature except for size-induced flexibility;by contrast,organic semiconductors are intrinsically soft and flexible but the electrical performance is poor.This is why the discovery of bulk plasticity in Ag2S at room temperature and ZnS in darkness is groundbreaking in solving this long-standing material dilemma between the mechanical deformability and the electrical performance.The present review summarizes the background knowledge and latest advances in the emerging field of plastic inorganic semiconductors.At the outset,we argue that the plasticity of inorganic semiconductors is vital to strain tolerance of electronic devices,which has not been adequately emphasized.The mechanisms of plasticity are illustrated from the perspective of chemical bonding and dislocations.Plastic inorganic materials,for example,ionic crystals(insulators),ZnS in darkness,and Ag2S,are discussed in detail in terms of their prominent mechanical properties and potential applications.We conclude the article with several key scientific and technological questions to address in the future study.

SnIP-type atomic-scale inorganic double-helix semiconductors: Synthesis, properties, and applications

Flexible inorganic double helical semiconductors similar to DNA have fueled the demand for efficient materials with innovative structures and excellent properties.The recent discovery of tin phosphide iodide(SnIP),the first carbon-free double helical semiconductor at an atomic level,has opened new avenues of research for semiconducting devices such as thermoelectric and sensor devices,solar cells,and photocatalysis.It has drawn significant academic attention due to its high structural flexibility,band gap in the visible spectrum range,and non-toxic elements.Herein,the recent progress in developing SnIP,including its prestigious structure,versatile and intriguing properties,and synthesis,is summarized.Other analogues of SnIP and SnIP-based hybrid materials and their applications in photocatalysis are also discussed.Finally,the review concludes with a critical summary and future aspects of this new inorganic semiconductor.

CARRIER PHOTOGENERATION IN POLY(N-VINYL-CARBAZOLE)-BASED PHOTOCONDUCTIVE THIN-FILM DEVICES

In this paper, photoexcitation processes in the bilayer devices based on inorganic materials and poly（N-vinylcarbazole） （PVK） were investigated. In order to clarify the roles of inorganic materials in photoconductive properties of bilayer devices, TiO2 and ZnS were chosen to combine with PVK. A model for generation of photocurrent （Iph） in single layer device of PVK was obtained. It is deduced that the recombination rate constant （Pcomb） and the ionization rate constant （y） ofexcitons should be considered as the most important factors for Iph. For inorganic materials （TiO2 or ZnS）/PVK bilayer devices, in reverse bias of-4 V, the photocurrent of 115 mA/cm^2 in the TiO2/PVK device was observed, but the photocurrent in the ZnS/PVK device was only 10 mA/cma under the illumination light of 340 nm and the light intensity of 14.2 mW/cm^2. The weaker photocurrent is attributed to the absorption of ZnS within UV region and the energy offset at the interface between PVK and ZnS, which impedes the transport of charge carriers.

Inorganic p-type semiconductors and carbon materials based hole transport materials for perovskite solar cells

Organic-inorganic lead halide based perovskite solar cells（PSCs） have presented a promising prospective in photovoltaic field with current record power conversion efficiency of 22.7%, which is comparable to commercial crystalline silicon cells and even higher than traditional thin film solar cells of CIGS. However,the pressure to enhance device stability under operational condition has driven researches towards development of stable hole transport materials（HTMs） for PSCs. Compared to traditional expensive organic HTMs such as spiro-OMeTAD, there is no doubt that inorganic p-type semiconductors and carbon materials are attractive alternatives that not only possess better stability but also are much cheaper. This review summarized the most recent progress of inorganic hole-transporting materials and carbon materials that have been developed for PSCs. The most recent advancement of device performance using these HTMs was demonstrated. In addition, the research of using various types of carbon materials as additives in HTMs to enhance device performance and stability or as electrical contact in HTM-free PSC was also demonstrated. The effectiveness of each type of materials on mitigating ion migration and degradation of PSC induced by humidity, illumination light intensity and high temperature is discussed.This timely review sheds light on the approaches to tackle the stability issue of PSCs to push the technology towards commercialization through material engineering of HTM.

Perovskite polariton parametric oscillator

Optical parametric oscillators(OPOs)have been widely applied in spectroscopy,squeezed light,and correlated photons,as well as quantum information.Conventional OPOs usually suffer from a high power threshold limited by weak high-order nonlinearity in traditional pure photonic systems.Alternatively,polaritonic systems based on hybridized exciton–photon quasi-particles exhibit enhanced optical nonlinearity by dressing photons with excitons,ensuring highly nonlinear operations with low power consumption.We report an on-chip perovskite polariton parametric oscillator with a low threshold.Under the resonant excitation at a range of angles,the signal at the ground state is obtained,emerging from the polariton-polariton interactions at room temperature.Our results advocate a practical way toward integrated nonlinear polaritonic devices with low thresholds.