溶劑對有機空間電荷限制電晶體之影響與超薄吸收層對有機太陽能電池之影響

Abstract

本論文針對兩種重要的有機電子元件進行研究，這些元件分別是有機垂直式電晶體與有機太陽能電池。第一部份，我們針對目前較為成功的垂直式電晶體來進行研究，也就是空間電荷限制電晶體(space-charge-limited transistor , SCLT)。SCLT 之工作原理和真空管三極體相似，其結構是在有機二極體中埋入金屬基極控制垂直方向的電流。然而，目前有機材料過低的垂直載子遷移率，導致此元件的輸出電流密度約只有1 mA/cm^2。在本論文中，我們將使用高沸點溶劑搭配solvent annealing 慢乾製程來製備主動層，讓材料在孔洞狀基極結構中的垂直載子遷移率從4×10-5 cm^2/V-s 大幅地提升到 2×10-3 cm2/V-s。此元件之輸出電流密度可高達100 mA/ cm^2 且仍維持其良好的開關比及電流增益。另外此元件可簡單的擴大其主動區至1cm^2 來輸出大電流供高功率元件使用。第二部份，我們藉由在N-type 和P-type 半導體的介面間放入吸收層，實現了一種新的有機太陽能電池概念。當入射光被吸收時，激子會在吸收層產生並拆解為電子-電洞對，接著經過傳輸通道被收集至電極導出。N-type 和P-type 半導 體分別為ZnO 及poly(9,9’-dioctylfluorene-co-N(4-butylphenyl)diphenylamine(TFB)，而Lead phthalocyanine (PbPc)則是做為吸收層。我們為了瞭解PbPc 和TFB 厚度對太陽能電池之特性的影響，於是將這兩種材料的厚度在相同結構下做了許多測試。最後我們發現在PbPc 厚度50 nm，TFB 厚度20 nm 時元件可表現出最佳的外部量子效應。

This work focus on the development of two important organic electronic devices those are organic vertical transistor and organic solar cell. In the first part, the influence of the solvent on the electrical characteristics of the polymer vertical transistor, namely polymer space-charge-limited transistor, is investigated. The space-charge-limited transistor (SCLT) is a solid-state version of vacuum tube triode, with a metal grid embedded in an organic diode to control its vertical current.However, so far its current density is only 1 mA/cm2 due to the poor vertical mobility of the polymer. In this dissertation we demonstrate that the polymer vertical mobility can be greatly enhanced by a slow drying process using high-boiling-point solvent, i.e. solvent annealing, in a textured surface with 200 nm scale defined by the base. The vertical columns promote the chain alignment of poly(3-hexylthiophene-2,5-diyl) (P3HT) during the slow solvent annealing and result in an ordered structure unattainable in planar substrate. The vertical mobility is raised from 4×10-5 cm^2/V-s to 2×10-3 cm^2/V-s and the SCLT can deliver output current density as high as 100 mA/cm^2 while maintaining good current gain and on-off ratio. With such high current density 100 mA current output can be delivered by a 1cm2 active area which is very easy to fabricate with high reliability. In the second part, a new hybrid solar cell concept is realized by using a layer of absorber lies at the interface between an n-type semiconductor and p-type semiconductor. The exciton, generated in the absorber as incident light is absorbed, transforms into a separated electron and hole pair and then driven through transport channels to the collecting electrodes. The n-type and p-type semiconductor is ZnO and poly(9,9’-dioctylfluorene-co-N(4-butylphenyl)diphenylamine (TFB) respectively. Lead phthalocyanine (PbPc) is utilized as absorber. Various thickness of PbPc and TFB are tested in order to understand the influence of PbPc and TFB thickness on the solar cell characteristics. It is found that 50 nm PbPc and 20 nm TFB result in highest external quantum efficiency (EQE).