有機光電流增益現象之探討與其在光偵測器的應用

Abstract

光偵測器的優點包含了可撓性，重量輕、容易攜帶，並且製程溫度低，可製作於可 撓性塑膠基板上。我們已發現在高分子與富勒烯混合物中加入一個近紅外光的有機染料 可達成高達8000%的光子增益現象，藉此製作的光偵測器初步的實驗結果已可達到非常 高的光響應度(28 A/W)。「有機光電流增益現象之探討與其在光偵測器的應用」之研究 計劃將系統性地研究此光子增益現象及對高分子光偵測器特性的影響。除了元件製作參 數的最佳化之外，也將量測元件的動態特性，高分子薄膜型態也會以原子力顯微鏡、穿 透式電子顯微鏡等方式研究，薄膜材料的深度剖面也將以穿透式電子顯微鏡及二次離子 質譜儀探討，更重要的是，我們也擬仔細探討此特殊的光子增益機制，我們將量測電容 電壓曲線以釐清電荷捕陷的可能性，也將製作電子及電洞元件藉以判斷電荷捕陷的狀 態，我們也擬製作不同金屬電極的元件，並藉由量測其特性之差異幫助機制的理解。在 計畫的第二年度，我們將以數種方式改善元件的效能與穩定度。包含製作電極緩衝層用 以降低漏電流，並分析元件的內部光電場的分佈，並經電場的最佳化增加元件的光吸 收，也擬藉由加入光學間隙層與金屬奈米粒子所誘導的表面電漿效應改善光子的吸收效 率，最後，我們也將量測元件生命期，並藉由自發生成的電極緩衝層改善元件的穩定度。 預計成功執行本計劃後高分子光偵測器的效率與元件生命期及穩定性都將被大幅改善。

We have found that adding a near-infrared organic dye into a polymer-fullerene blend can achieve photomultiplication (PM) (more than 8000%) under a low applied voltage. The initial result of the organic photodetector has demonstrated an extremely high responsivity of 28 A/W at 550 nm. The “study of photomultiplication in organic materials and its application in photodetection” research project will aim to systematically investigate the mechanism of the PM phenomenon in organic materials and its effects on the device performance of polymer photodetectors. The device performance will be firstly improved by optimizing the fabrication processes. The dynamic response of the photodiode will be measured and further improved. The morphology of the polymer films will be examined by atomic force microscopy and scanning electron microscopy (SEM). The depth profile will be also studied by SEM and secondary ion mass spectrometry. More importantly, the PM mechanism will be thoroughly studied. The possible charge trapping will be analyzed by capacitor-voltage measurements under illumination. Hole/electron-only devices will be fabricated and measured for further identification of the trapped charge states. In the second year, the device performance will be further improved by several approaches. Buffer layers on the electrodes will be made for inhibiting the leakage current. For improving the photon absorption efficiency, optical electric field in the device structure will be analyzed and optical spacers will be inserted into the device. Additionally, surface plasmonic effect induced by the introduction of metal nanoparticles will be also employed. Finally, the lifetime of the devices will be measured and the device stability will be improved by introducing a spontaneously formed electrode buffer layer. The device efficiency and device lifetime of the highly sensitive organic photodetectors are anticipated to be improved significantly after the success of this project.