Numerical Study of Optimization of Layer Thickness in Bilayer Organic Light-Emitting Diodes

A numerical model for bilayer organic light-emitting diodes (OLEDs) is developed under the basis of trapped charge limited conduction.The dependences of the current density on the layer thickness,trap properties and carrier mobility of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure anode/HTL/EML/cathode are numerically investigated.It is found that,for given values of the total thickness of organic layers,reduced depth of trap,total density of trap,and carrier mobility of HTL as well as EML,there exists an optimal thickness ratio of HTL to EML,by which a maximal quantum efficiency can be achieved.Through optimization of the thickness ratio,an enhancement of current density and quantum efficiency of as much as two orders of magnitude can be obtained.The dependences of the optimal thickness ratio to the characteristic trap energy,total density of trap and carrier mobility are numerically analyzed.

Variation of Soil Labile Organic Carbon Pools along an Elevational Gradient in the Wuyi Mountains,China

土壤活性有机碳(LOC)是一组活跃的化学物质,由于其较短的周转时间和对环境变化的敏感性在全球碳循环中发挥着重要的作用。但是,对活性有机碳在亚热带森林沿海拔梯度的空间变异还缺乏了解。在本研究中,我们测定了福建武夷山自然保护区不同海拔高度具有代表性的中亚热带常绿阔叶林(500 m)、针叶林(1150 m)、亚高山矮林(1750 m)以及高山草甸(2150 m)土壤不同土层(0-10,10-25和25-40 cm)中微生物可利用碳(MAC)、微生物量碳(MBC)、易氧化碳(ROC)、水溶性碳(WSOC)和轻组碳(LFC),并观测了相应的植物凋落物质量(LM),土壤温度和湿度。结果表明:沿海拔梯度的植被变化和土层深度变化对土壤活性有机碳有显著的影响。微生物可利用碳、微生物量碳、易氧化碳和水溶性碳在不同土层均沿海拔高度的增加而显著增加;而低海拔的常绿阔叶林和针叶林中轻组碳的含量高于亚高山矮林和高山草甸的轻组碳的含量。各土壤活性有机碳库均随土层的加深而减小。除轻组碳外,各碳库间存在着极显著的正相关(p【0.001)。轻组碳分别在低海拔(常绿阔叶林和针叶林)和高海拔(亚高山矮林和高山草甸)与各碳库显著相关。