本研究探討主動層上覆蓋電荷萃取層(聚乙烯亞胺, PEI)後，主動層的微結構變化及PEI的薄膜特性對有機太陽能電池的電特性之影響，聚(3-己烷噻吩) (Poly (3-hexylthiophene), P3HT)摻雜碳六十衍生物([6,6]-phenyl C61-butyric acid methyl ester, PCBM)為主動層材料，使用的溶劑為氯苯。首先比較主動層有無覆蓋PEI的電子萃取能力，並進一步改變PEI的製程參數，包括濃度、熱烤溫度、熱烤時間及氧電漿處理條件，將PEI的薄膜特性優化。接著比較不同電荷萃取層對元件特性的影響，最後將PEI應用於不同主動層系統的有機太陽能電池。我們使用吸收光譜儀、拉曼光譜儀、X光繞射儀和原子力顯微鏡對薄膜進行分析，並進一步分析其相對應太陽能電池元件的電特性。
由薄膜的分析結果發現，主動層覆蓋PEI後，P3HT在非結晶區的結構均勻性變差，而結晶區的均勻性變好，但不影響主動層薄膜的表面形態。此外，PEI層能有效萃取主動層的電子並阻擋電洞，使元件的短路電流由5.04 mA/cm2提升至8.35 mA/cm2，與填充因子由0.28提升至0.64。在PEI的製程參數優化中，我們發現改變PEI的製作條件，不會影響主動層的微結構及表面形貌。以濃度0.01 wt%製備的PEI薄膜，具最佳化的電子萃取與電洞阻擋能力。PEI的熱烤溫度條件與其熔點(60 oC)有關，在90 oC時PEI可均勻覆蓋於主動層上，使元件效率最佳。PEI的熱烤時間為20分鐘時，PEI可以完全熔解並均勻覆蓋於主動層上，使元件效率最好。而主動層表面的氧電漿處理，我們發現隨施打氧電漿的總能量提升，主動層會產生缺陷，使元件特性變差。故選擇適當的PEI參數，可以有效提升元件效能。
接著我們比較以PEI或Ca作為電子萃取的元件特性。覆蓋Ca的元件，其外部量子效率值最高約50 %，轉換效率僅為2.36 %。而覆蓋PEI元件，其外部量子效率可進一步提高至60 %，因此電子可以有效的被萃取出來，提升元件的短路電流，轉換效率可達3.17 %。在大氣下的元件穩定性測試，我們發現Ca作為傳輸層的元件相當容易受空氣中水氧的影響，因此覆蓋上Ca的元件不到30分鐘就已測量不到電性。而覆蓋上PEI的元件，約三個小時過後，仍保有50 %的電性，七個小時後才量不到元件電性，故其在大氣下的穩定性明顯優於覆蓋上Ca的元件。
最後將PEI應用於主動層為P3HT:PCBM，溶劑為鄰-二氯苯(1,2-dichlorobenzene, DCB)，及主動層為P3HT混摻茚-碳六十之雙加成物(Indene-C60 bisadduct, ICBA)的太陽能電池元件，同樣具有電子有效被萃取出來的效果，提升元件的短路電流，轉換效率分別達2.76 %與4.13 %。

In this study, polyethylenimine (PEI) was used as a charge extraction layer and deposited on the active layer of poly(3-hexylthiophene) (P3HT):(6,6)-phenyl C61-butyric acid methyl ester (PCBM). The influences of the microstructures of the active layer and the properties of the PEI thin film on the photovoltaic properties of the P3HT:PCBM solar cells were investigated.

The electron extraction efficiency of the specimen with PEI was compared with that without PEI. The process parameters of a PEI thin film, including solution concentration, baking temperature, baking time, and oxygen plasma treatment, were then modified to optimize the thin film properties. The photovoltaic performance of the device with PEI was finally compared with that of the device with calcium as an electron extraction layer.

The analysis of the current distribution on the thin film surface shows that the electron extraction and the hole blocking in the cathode of the device with PEI were enhanced compared with that without PEI. The device with PEI exhibited improved short circuit current density (5.04 mA/cm2 → 8.35 mA/cm2), fill factor (0.28 → 0.64), and power conversion efficiency (0.70% → 3.17%).

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