Current-Voltage Characteristics of Carrier Transport in Organic Light-Emitting Devices

本論文著重載子傳導反應在電流電壓特性上的研究。我們回顧與發展了兩種常見的空間電荷限制電流(SCLC)理論。第一個理論是SCLC搭配指數分佈陷阱的模型，我們發展了正確的解析解，與傳統的近似解相較，我們指出近似解低估了電流的大小，並低估了電流電壓曲線的參數l。第二個理論是SCLC搭配Poole-Frenkel的效應，修改後的電性曲線指出高壓下的電流將正比於溫度。對這兩者理論而言，未來研究電流-電壓-溫度(J-V-T)將有助於澄清這兩種模型的可行性。我們利用前者的模型配合我們實驗的數據，結論熱致電子濃度(n0)與移動率(u0)的乘積約在6.5×10^4 ~ 8×10^5 (/ V s cm)之間。This thesis focuses on the current-voltage characteristic of carrier transport. Two common SCLC theories are overviewed and developed. For the case of space charge limited current (SCLC) with exponential trap distribution, we develop the analytical solution, indicating that the traditional approximation underestimates the current magnitude and underestimates the parameter l in the model. For the case of SCLC coupled with Poole-Frenkel effect, the refined solution at high bias indicates the current depends on the temperature directly. For both cases, studying J-V-T will justify the validity of these models. We use the former model to ‾t our experiment data, and conclude that the product of thermal generated electron concentration and the mobility to be around 6.5x10^4 ~ 8x10^5(/cm V s).1 Introduction 6 2 Devices, experimental methods, and materials 10 2.1 Devices:Al/Alq3/Al 11 2.2 Experimental methods: thermal evaporation 13 2.3 Materials 18 2.3.1 Aluminum 18 2.3.2 Alq3 19 3 Carrier transport 22 3.1 Trap free SCLC theory 25 3.1.1 Ohm's Law 31 3.1.2 Mott-Gurney Law 32 3.2 A transformation and the scaling law 35 3.2.1 the slope of J-V 40 3.3 TCLC theory 41 3.3.1 J-V of TCLC with exponential trap distribution 44 3.3.2 Arguments for TCLC with exponential trap distribution 58 3.4 Field-dependent SCLC theory 60 3.4.1 J-V of SCLC with Poole-Frenkel type mobility 62 3.4.2 Arguments for SCLC with PF type mobility 67 3.5 Simulation strategy: tricks and the philosophy 69 3.6 Conclusion 71 4 Result and discussion 73 4.1 Fitting to experiment data and discussion 73 4.2 Conclusion and future work 8