有機太陽能電池薄膜形態之修飾與效率提升

太陽能電池發展至今，仍以結晶矽太陽能電池為主流，然而最大缺點在於生產成本太高。有機高分子太陽能電池則提供另一種發電方式，其製程簡單、成本低廉，且具有透光性、大面積製造及可撓性的優點，顯示其巨大的發展潛力。在本論文中，我們藉由一種新的外加電場處理方式來提升有機高分子太陽能電池的效率表現，與先前的文獻比較，使用此處理方式的優點在於避免造成元件電極的破壞，還能夠配合有機高分子材料的極性方向來施加。我們利用化學軟體HyperChem (Hypercube Inc.)分析有機分子材料的極性方向，並針對極性方向進行外加水平方向電場處理，成功的提升元件效率。使用外加水平方向電場處理對於有機吸光層薄膜的表面形態有兩個重要的修飾：第一是當外加水平方向電場後，有機高分子材料會由於極性而受到電場影響而移動，且有機高分子材料主鏈會沿著有機吸光層薄膜表面垂直方向規則排列，因此載子便能經由主鏈有效且快速的傳遞到相對應的電極，提高載子遷移率。第二是由於有機高分子材料移動而造成薄膜表面粗糙度提升，由原子力顯微鏡圖分析，外加時間長短與方均根粗糙度大小有關，而越大的方均根粗糙度則表示有機吸光層薄膜與電極的接觸面積會增加，使載子可以快速且大量的被電極捕捉形成光電流。因此，藉由外加強度為10000 V/m水平方向電場處理，能夠提升以P3HT:PCBM混摻溶液製作之倒置結構有機高分子太陽能電池的光電轉換效率到達4.16 %，其開路電壓為0.57 V，短路電流為11.9 mA/cm2，填充因子為61.3 %。論文的最後，我們使用台灣大學材料所趙基揚教授團隊提供的PBF低能隙有機高分子材料，應用在倒置結構有機高分子太陽能電池上，並藉由調整有機吸光層混摻比例與預熱溫度，在不同旋塗轉速下找到最佳的製作參數，最後再使用外加電場處理改善元件表現。

關鍵字

有機高分子太陽能電池；倒置結構；表面形態；外加電場；低能隙

並列摘要

Up to the present, silicon crystal solar cells still play the major role in the field of development of photovoltaic devices. However, high production cost of these cells is a major drawback. Polymer solar cells provide an alternative which has the advantages including: easy fabrication, low cost, pervious to light, large area fabrication, and flexibility; therefore, shows a great potential in future development. In this thesis, we will adopt a new method of applying an external electric field to enhance the performance of solar cells. Compared with previous references, this method has an advantage of avoiding damage caused to the electrodes of the device; furthermore, the electric field can be applied in conformity with the polarity direction of the polymer material. We succeeded to increase the device‘s efficiency by applying a horizontal external electric field, which its direction is determined by utilizing a chemical software HyperChem(Hypercube Inc.) to analyze the polarity of the polymer material. Applying a horizontal external electric field has two effects on the surface morphology of the polymer light-absorbing thin film. One is that after the electric field is applied, polymer molecules will be affected because of their polarity; thus, a shift occurs. The main chain of the polymer will align vertically against the polymer light-absorbing thin film surface. Hence, carriers will be able to transfer to their corresponding electrodes efficiently and increase carrier mobility. Second, the shift causes the roughness of the thin film surface to increase. According to the AFM images, the electric field applying time is relevant to the RMS roughness. As the RMS roughness increases, the contact area of the polymer light-absorbing thin film surface and the electrode increases, carriers are then collected quickly and turned into photo current. As a consequence, by applying a horizontal external electric field of magnitude 10000 V/m can increase the PCE of an inverted structured P3HT:PCBM polymer solar cell up to 4.16 %, and it‘s Voc is 0.57 V, Jsc is 11.9 mA/cm2 and FF is 61.3 %. At the end of this thesis, we employed PBF, which is a low band gap material provided by Professor Chao Chi-Yang and his group, on inverted structured polymer solar cells. Optimal parameters were determined by adjusting the mixing ratio of the active layer, preheating temperature, and spin-coat rotational speed. Lastly, the device was improved by applying an electric field.