Hole transporting layer plays a crucial role to realize high efficiency and long lifespan by balancing the charge carrier into the desired recombination zone.

Organic light emitting diodes (OLEDs) have been well known for their potential usage in the lighting and display industry. The device efficiency and lifetime have improved considerably in the last three decades. However, for commercial applications, operational lifetime still lies as one of the looming challenges. In this review paper, an in-depth description of the various factors which affect OLED lifetime, and the related solutions is attempted to be consolidated. Notably, all the known intrinsic and extrinsic degradation phenomena and failure mechanisms, which include the presence of dark spot, high heat during device operation, substrate fracture, downgrading luminance, moisture attack, oxidation, corrosion, electron induced migrations, photochemical degradation, electrochemical degradation, electric breakdown, thermomechanical failures, thermal breakdown/degradation, and presence of impurities within the materials and evaporator chamber are reviewed. Light is also shed on the materials and device structures which are developed in order to obtain along with developed materials and device structures to obtain stable devices. It is believed that the theme of this report, summarizing the knowledge of mechanisms allied with OLED degradation, would be contributory in developing better-quality OLED materials and, accordingly, longer lifespan devices.

Food security is one of the burning issues in the 21st century, as a tremendous population growth over recent decades has increased demand for food production systems. However, agricultural production is constrained by the limited availability of arable land resources, whereas a significant part of these is already degraded due to overexploitation. In order to get optimum output from the available land resources, it is of prime importance that crops are monitored, analyzed, and mapped at various stages of growth so that the areas having underdeveloped/unhealthy plants can be treated appropriately as and when required. This type of monitoring can be performed using ultra-high-resolution earth observation data like the images captured through unmanned aerial vehicles (UAVs)/drones. The objective of this research is to estimate and analyze the above-ground biomass (AGB) of the wheat crop using a consumer-grade red-green-blue (RGB) camera mounted on a drone. AGB and yield of wheat were estimated from linear regression models involving plant height obtained from crop surface models (CSMs) derived from the images captured by the drone-mounted camera. This study estimated plant height in an integrated setting of UAV-derived images with a Mid-Western Terai topographic setting (67 to 300 m amsl) of Nepal. Plant height estimated from the drone images had an error of 5% to 11.9% with respect to direct field measurement. While R2 of 0.66 was found for AGB, that of 0.73 and 0.70 were found for spike and grain weights respectively. This statistical quality assurance contributes to crop yield estimation, and hence to develop efficient food security strategies using earth observation and geo-information.

The realization of highly efficient devices depends on efficient charge carrier injection, employment of materials, and proper fabrication methodologies. However, it is difficult to manufacture highly efficient large-area devices due to the varied thickness of organic layers and low mobility of charge carriers. Solution and thermal evaporation processes have been reported for the fabrication of highly efficient and long-lifetime organic light-emitting diodes (OLEDs). This work reveals appropriate performance enhancement by employing solution-processable nanocomposite, i.e., titanium oxide (TiO 2 ) nanoparticles embedded in 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) as an electron-transport layer with high electron mobility and good compatibility with the yellow emissive layer. Topographies of TiO 2 -doped TPBi films with different doping concentrations are observed after annealing at 60 °C. The device using a 20 wt % TiO 2 -doped TPBi exhibits maximum power efficacy of 56.1 lmW −1 , current efficiency of 53.9 cdA −1 , and external quantum efficiency of 15.4%, while that without TiO 2 nanoparticles showed values of 37.0 lmW −1 , 35.1 cdA −1 , and 10.8%, respectively. The enhancement may be attributed to improved electron mobility, efficient hole-blocking, and reduced barrier height. The solution-processable TiO 2 -doped TPBi may lead to an efficient fabrication strategy for next-generation lighting and display applications.

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