Synthesis and Characterization of Poly(2,3-diphenyl-1,4-phenylene vinylene) and Naphthalene Diimide Derivatives with Dendritic Side Chains and Study on Porphyrin-based Copolymer Applied in Ternary Blend Polymer Solar Cells
|關鍵字:||聚(2,3-雙苯基-1,4-仲苯基乙烯);螢光量子效率;樹枝狀側鏈;萘環亞醯胺化合物;紫質高分子;三元混摻薄膜太陽能電池;Poly (2,3-diphenyl-1,4-phenylene vinylene);Photoluminescence efficiency;Dendritic side chain;Naphthalene diimides;Porphyrin-incorporated polymers;Ternary-blend polymer solar cells|
|摘要:||本論文由三部份研究所組成:第一部份探討聚(2,3-雙苯基-1,4-仲苯基乙烯)衍生物P1–P3之固態相結構和光物理性質的關係。P1為文獻已知的高亮度、高螢光量子效率之DP6-PPV，P2和P3則是新穎的DP-PPV衍生物分別含疏水和親水性樹枝狀側鏈基。P1–P3在氯仿溶液中其螢光量子效率 > 80 %，在薄膜態下也 > 63 %以上，但將高分子加熱熔融後冷卻至室溫，P1和P3其螢光效率顯著地下降。藉由DSC的相行為分析和WAXD相結構判定，我們發現P1和P3產生了規則的相結構，而造成螢光效率下降；令我們驚訝的是，P2仍能保有高螢光量子效率，既使在規則的相結構。由P2的相結構分析發現，其原因為疏水性樹枝狀側鏈能有效干擾DP-PPV高分子主鏈間π−π堆疊的分子間作用力。由螢光衰變時間實驗也能證明P2所產生的激子更能有效限制在放光過程，而較少以其他不放光形式消耗。
第二部份合成含氟側鏈及含氟樹枝狀側鏈之環延伸萘環亞醯胺化合物。萘環亞醯胺化合物為文獻上報導具高電子遷移率之材料，引進雙邊含氟側鏈的第一代樹枝狀分子取代基，並改變柔軟段長短，增加材料的溶解度，希望能藉由簡單的濕式製程將材料製作於元件上。由DSC和POM我們可初步地判斷TBNDIs和BDTDYBMNDIs之基本分子結構排列，由UV-Vis光譜和CV我們可知其基本光學和電化學性質，BDTDYBMNDIs其LUMO值約在－4.41到－4.45間，相當適合作為n型OFET之材料，我們製作單一電荷傳輸元件並利用空間限制電流公式，計算其電子遷移率介於10-5－10-6 cm2 V-1 s-1間。待我們藉由XRD將其利用親疏氟效應和柔軟段長短，產生的分子自組裝堆疊排列解析，再搭配電性測試元件，相信其會是相當重要的研究成果。
第三部份我們合成出以紫質為高分子主鏈組成單元之新穎高分子PPor-DITT。PPor-DITT/PC71BM之二元混摻PSCs元件和文獻已知以紫質為高分子主鏈組成單元之高分子材料(PPors)一樣，有低的PCE值之問題。藉由螢光消去實驗和利用原子力顯微鏡分析主動層表面形貌，我們發現PPor-DITT/PC71BM摻混的主動層能有效使載子生成和轉移，但不理想的主動層形貌使載子不易傳輸，提供PPors之PSCs元件可藉由主動層形貌的改善而提升元件表現的想法。利用PPor-DITT其在藍光波段400－550 nm有強的特徵吸收峰，將其作為藍光區的吸收添加劑，應用在三元混摻之PSCs元件中。無定形高分子PTPTPTDPP為主吸光材料之系統中，摻入2 wt%的PPor-DITT，可增加10 %短波長區量子轉換效率，且能有效維持其Jsc和FF值。相反地，在具結晶性的P3HT為主吸光材料之系統中，摻入PPor-DITT會使P3HT結晶性下降，導致FF和PCE值大幅下降。此部份研究對PPors在PSC元件的應用提供另一選擇，作為藍光區的吸收添加劑，並用於無定形高分子為主吸光材料之三元混摻系統中。|
The thesis is composed of three topics. In the first part, to understand the relation between the solid-state phase structures and the photophysical properties of Poly (2,3-diphenyl-1,4-phenylene vinylene) (DP-PPV) derivatives, three DP-PPV derivatives, P1-P3 were designed, synthesized via Gilch polymerization and characterized. Among the polymers, P1 is a reported highly emissive poly(2,3-diphenyl-5-hexyl-p-phenylene vinylene), and P2, and P3 are novel DP-PPV derivatives, which are purposely designed to bear hydrophobic and hydrophilic Percec-type dendrons at the 5-position of the phenylene units on their DP-PPV main chains. The bulkiness and hydrophobic-hydrophilic natures of the side chains show strong effects on photophysical properties of the polymers. The solutions and as-casted films of P1-P3 all show remarkably high photoluminescence (PL) efficiency (ΦPL) (> 80 % in chloroform solution, and > 63 % for the as-casted films) among the PPV-derivatives. However, ΦPL of P1 and P3 decrease significantly to 30 % after cooled their polymer melts to room temperature. Through the phase behavior analysis by differential scanning calorimetry (DSC), and phase structure analysis by wide angle X-ray diffraction (WAXD), the decrease of ΦPL can be elucidated and attributed to the ordering of the solid-state structures of P1 and P3. To our surprise, ΦPL of P2 is preserved even in an ordered solid-state phase, and it is insensitive to the structural ordering. Structural analysis by WAXD patterns of P2 revealed that the aliphatic dendritic side chains of P2 effectively disturbing the intermolecular π-π interactions among the conjugated backbones, which allows the preservation of ΦPL in the environment with ordered packing of DP-PPV molecules. The results of time-resolved PL decay experiments also confirmed that P2 possess long-lived decay time because of excitons confined more effectively for emissive emission. In the second part, the novel core-expanded naphthalene diimide derivatives containing fluorinated alkane or dendron were synthesized and characterized. Naphthalene diimides (NDIs) are excellent n-type materials applied in organic semiconductors. Introducing fluorinated dendron with different spacer into NDIs is to improve the solubility for the fabrication of solution-processd devices. We can preliminarily speculate their molecular arrangement in the crystalline phase by the analysis of DSC and POM. The information of optical and electrochemical properties were obtained from UV-Vis spectra and cyclic voltammograms, respectively. The LUMO values of BDTDYBMNDIs in the range of －4.41－－4.45 eV are suitable n-type materials for the application of OFET device. The electron-only devices were fabricated to achieve the electron mobilites by space charge limited current equation. The fluorous phase of the dendron mediates the self-assembly process by means of the fluorophobic effect and the structural analysis of XRD is stll in process. Combining electronic measurement with structural analysis will make this research important. In the third part, porphyrin, despite chosen by nature as light harvesting units, has not revealed its full potentials as a structural unit in porphyrin-incorporated polymers (PPors). Polymer solar cells (PSCs) utilizing PPors suffer from their low Jscs and FFs. To investigate the origins of the low performances and take the advantage of the strong Soret band absorption in the blue-light region, a novel PPor, PPor-DITT, were synthesized, characterized and used as a blue-light harvesting dopant in the ternary-blend PSCs. PPor-DITT features broad absorption in the blue-light region, because the Diindenothieno[2,3-b]thiophene (DITT) unit extended the conjugation in the polymer backbone. PPor-DITT/PC71BM based PSCs have a high Voc of 0.79 V, but limited Jsc of 2.98 mA cm-2, and FF of 0.33. The low Jsc and FF were attributed to the un-optimized morphology, as the PL quenching experiments demonstrated efficient electron transfer from the photoexcited PPor-DITT to PC71BM, but smooth AFM topography of PPor-DITT/PC71BM blend indicated the ideal interpenetrating network for charge transport was not reached. Using PPor-DITT as a blue-light harvesting dopant in an amorphous host leverage the strong 400–550 nm absorption band of PPor-DITT and circumvent the difficulties in reaching optimized morphology in the PPor/PCBM thin films. An addition of 2 wt% of PPor-DITT in ternary-blend PSCs resulted in a 10 % increase of EQE in the blue-light region, good Jsc of 7.98 mA cm-2, and FF of 0.59. On the contrary, in a crystalline host (P3HT), the PPor-DITT dopant significantly decreased the crystallinity of the host and led to large drops in FF and PCE. The study provides an alternative route and expands the application of PPors in PSCs as a blue-light harvester in ternary-blend PSCs using amorphous polymers as host.
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