本論文之主要研究目標為：摻雜四氧化三鐵磁性奈米粒子於有機太陽能電池特定薄膜結構中之效應。由於四氧化三鐵奈米粒子具有超順磁特性，且在標靶藥物治療及核磁共振等生醫領域方面有其特殊應用價值，因此期望藉由其所具備之磁特性與元件中所產生之光電流產生電磁交互作用以提升元件之光電轉換效率。
在本實驗中，我們成功地以化學共沉澱法合成出親水性Fe3O4 MNPs與疏水性OA-Fe3O4 MNPs，兩種粒子之平均粒徑皆約為10 nm左右，具備奈米級材料所特有之超順磁特性並經過SQUID VSM之驗證。親水性和疏水性之粒子分別以不同重量百分濃度均勻地分散於PEDOT:PSS與P3HT:PCBM溶液之中，本實驗皆採用異質接面(BHJ)結構，以PEDOT:PSS:Fe3O4 MNPs與P3HT:PCBM:OA-Fe3O4 MNPs溶液分別做為元件之電洞傳輸層及主動層材料。
實驗結果發現將0.5 wt%及1 wt%之OA-Fe3O4 MNPs摻雜入P3HT:PCBM之後，其分別對一般正向摻雜元件產生了>20%及>40%之效率提升。接著對摻雜不同wt% OA-Fe3O4 MNPs之主動層薄膜進行：FTIR、cryo-TEM、AFM、UV-Vis、PL及SAXS等材料分析，發現主動層薄膜之化學結構並不因為摻雜而改變，但局部表面形貌及相分離微結構則因為OA-Fe3O4 MNPs摻雜濃度提升而受到影響。在0.5 wt%及1 wt%摻雜濃度下之主動層薄膜，其光吸收能力明顯提升但再結合過程所放出之螢光強度卻受到抑制，此為摻雜元件效率提升之主因。而OA-Fe¬3O4 MNPs摻雜主動層之各項薄膜分析結果皆與元件特性之表現相呼應。
在本研究中我們推論主動層光吸收能力提升之主因來自於0.5 wt%及1 wt%之OA-Fe¬3O4 MNPs摻雜，使得P3HT之結晶性提高且結晶之domain size增大；而PL強度降低則源自於PCBM大規模擴散入P3HT matrix並團聚。另外我們也提出一假想模型：自旋電子在有機太陽能電池元件之再結合過程中扮演重要角色，且可以藉由摻雜超順磁性之四氧化三鐵奈米粒子來催化內系統跨越(ISC)機制，使三重電荷轉移態之比例大於單重態，進而抑制單重電荷轉移態再結合回到基態之比例，螢光強度降低且光電流之損耗減少，元件之短路電流及光電轉換效率因而提升。

The main purpose of our research focused on the effect of doping Fe3O4 magnetic nanoparticles (MNPs) into the assigned films of organic solar cells. Owing to the promising superparamagnetic characteristic and versatile applications in targeted therapy and MRI of Fe3O4 MNPs, we anticipate the photocurrent generated within the devices will induce electromagnetic interactions with dopants and raise the efficiency.
In our experiments, we successfully synthesized the hydrophilic Fe3O4 MNPs and hydrophobic OA-Fe3O4 MNPs by chemical co-precipitation method. The average diameter of both kinds of the as-synthesized particles is around 10 nm that possess superparamagnetism confirmed by SQUID VSM. The hydrophilic and hydrophobic particles were dissolved into PEDOT:PSS and P3HT:PCBM solutions with different weight percentages used as hole transport layer and active layer in bulk heterojunction (BHJ) structure, respectively.
The results exhibited PCE of devices which doped with 0.5wt% and 1wt% OA-Fe3O4 MNPs in P3HT:PCBM under conventional processing was raised by >20% and >40%, respectively. The doped active layers were further analyzed by FTIR, Cryo-TEM, AFM, UV-Vis, PL, and SAXS. From those measurements, we could figure out the chemical compositions of OA-Fe3O4 MNPs doped active layers were not changed with doping percentage but local surface morphology, particle dispersibility and microstructure were varied. Advanced light absorbability and suppressed PL intensity of 0.5wt% and 1wt% doped active layers were the main reasons why PCE was improved. The results of all the measurements were consistent with the devices performances.
In this research, we figured out the enhanced light absorbability was attributed to the improved P3HT crystallinity and crystallite domain size from SAXS measurements. The suppressed PL intensity was ascribed to the large-scale diffusion of PCBM into P3HT matrix to form aggregates. Furthermore, we offer an inferential model to interpret the relationship between the energy band and spintronics of the used organic semiconductor material. We infer that “The intersystem crossing (ISC) mechanism between singlet (1CT) and triplet (3CT) charge transfer state can be catalyzed by doping OA-Fe3O4 MNPs into P3HT:PCBM. The altered ratio of 3CT/1CT by ISC will affect the recombination process of electron hole pairs and will further suppress the loss of photocurrent.”

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