噻吩及醯亞胺系電子施體/受體高分子材料之合成、形態及其光電元件應用

Abstract

含電子施體與受體之有機高分子材料為被廣泛研究之項目，透過不同的分子結構設計來調控的光電性質和良好的可加工性。然而，關於不同的材料結構及所形成奈米微結構所造成的影響尚未被深入研究。因此，此論文之研究目標為: I. 藉由引入含噻吩結構材料控制P3HT/PCBM系統之微結構以提升太陽能電池特性: 我們分別導入三嵌段共聚物PTPA-P3HT-PTPA，雙嵌段共聚物P3HT-b-P3PyT，小分子PCBTE、PCBBTE和PCBTTE等不同相容劑於P3HT/PCBM系統調控所形成PCBM微結構以提升太陽能電池元件的長期穩定性。當在P3HT/PCBM系統混入適量PTPA-P3HT-PTPA、P3HT-b-P3PyT、PCBTE、PCBBTE和PCBTTE，在光照AM 1.5G (100mW/cm2) 標準下可使太陽能電池最高效率分別達到4.4%、3.95%、3.86%、4.08% 和4.37%。並從DSC、TEM、光學顯微鏡、AFM的分析成果發現，在添加適量相容劑於P3HT/PCBM系統時，可避免PCBM大量聚集，形成由具有較大的表面積能夠幫助電子/電洞對分離的結構。添加相容劑進入P3HT/PCBM系統，除了元件效率有明顯的提升，亦能大幅改善電池元件的空氣穩定性與熱穩定性。在所有太陽能電池元件中，發現使用PCBTTE作為相容劑可使電池效率及穩定性達到最佳化，主要是由於PCBTTE具有明顯一端親P3HT及一端親PCBM的性質，避免PCBM產生聚集，此外，並由於PCBTTE非共軛鏈段比例相對小，可避免破壞P3HT/PCBM系統的電性。 II. 設計及合成新型施體-受體高分子材料並應用於非揮發性記憶體元件: 我們成功設計並合成一系列共軛高分子P3HT-b-P3PT及無規共聚醯亞胺高分子PI-NTCDIX並應用於阻抗式記憶體元件上。P3HT-b-P3PT部分，從P3HT-b-P3PT的場效電晶體原件在固定Vds下，來回掃描，發現有很明顯的遲滯現象，主要原因為P3PT鏈段對電荷有捕捉能力。隨著P3HT鏈段比例增加，記憶體原件性質會從動態隨機存取(DRAM)揮發性記憶體元件變成半導體，顯示無規排列的P3PT鏈段扮演電洞捕捉的角色。純P3HT-b-P3PT應用在記憶體原件顯現動態隨機存取(DRAM)揮發性記憶體特性，接著加入少量PCBM 混摻，會和PCBM產生電荷轉移效應(charge transfer)，進而元件性質轉換為一次寫入與多次讀取(WORM)非揮發性記憶體性質性質。PI-NTCDIX部分，藉由設計與合成無規共聚醯亞胺高分子PI-NTCDIX應用於阻抗式記憶體元件。並藉由改變NTCDI在高分子結構中所占的比例，調整其光學及電化學性質。記憶體元件結構分別以鋁金屬分別作為上下電極，發現隨著NTCDI的比例逐漸增加，記憶體元件性質會從原先揮發性轉變成一次寫入與多次讀取(WORM)的非揮發性記憶體性質，其雙穩態的導電度特性主要原因為形成電荷轉移複合物(charge transfer complex)，而元件易揮發程度與否則決定於所形成的電荷轉移複合物是否穩定。因為NTCDI的LUMO能階相對低，使得回復電荷轉移(back transfer complex)的能障增加，因而避免所形成電荷轉移複合物產生回復電荷轉移現象。由上述實驗結果證實經由調整施體與受體間電荷轉移的強度與穩定度可調整記憶體元件的揮發物性。

Donor-acceptor (D-A) polymers have attracted significant scientific interest recently because their electronic and optoelectronic properties can be manipulated through intramolecular charge transfer (ICT). However, the correlation between the chemical structure, morphology, and optoelectronic properties has not been fully explored yet. In this thesis, we address the above issue by exploring the following subjects: I. Morphology control of poly(3-hexylthiophene)/PCBM blends for enhancing the solar cell characteristics using thiophene-based surfactant: We used the triblock copolymer PTPA-P3HT-PTPA, diblock copolymer P3HT-b-P3PyT, small molecules PCBTE, PCBBTE, and PCBTTE as surfactants to control the morphology of PCBM in P3HT/PCBM blend and enhance the long-term stability of solar cell devices. The optimized PCE of the PTPA-P3HT-PTPA, P3HT-b-P3PyT, PCBTE, PCBDTE, and PCBTTE blended system reached up to 4.4%, 3.95%, 3.86%, 4.08%, and 4.37% under illumination of AM 1.5G (100mW/cm2). DSC, TEM, optical microscopy, and AFM were used to confirm these surfactants could reduce the interfacial energy to prevent domain coarsening and macrophase separation in an active layer depending on their contents. The increased PCE, combined with good air and thermal stability of solar cell devices by using the surfactants, indicates their promising potential for polymer solar cells. This best performance (stability and PCE value) among solar cell devices is using PCBTTE as surfactants blended with P3HT/PCBM, which is due to PCBTTE is an effective interfacial agent for dispersing and fixing the P3HT and PCBM domains in thin films and the minimal insulating linker between the electrically active moieties. II. Design and synthesis of new D-A polymeric systems for nonvolatile memory device applications. We have successfully designed and synthesized a series of conjugated polymers P3HT-b-P3PT and random copolyimides PI-NTCDIX, and used them for resist-type memories. For the P3HT-b-P3PT, the charge trapping of the P3HT-b-P3PT based memory devices may be occurred within the amorphous P3PT domains dispersed in the block copolythiophene by preventing charge transport. P3HT52-b-P3PT39 and P3HT102-b-P3PT37 exhibited the DRAM behaviours, suggesting that the significant effect of the amorphous P3PT segments on the electrical switching behavior. By blending a small amount of PCBM into P3HT-b-P3PT, the memory devices showed a WORM behavior. The mechanism associated with the memory characteristics was the charge transfer from the P3HT-b-P3PT donor to the PCBM acceptor, which stabilized the charge separated state for a long time during the ON stage. For the PI-NTCDIX (where X=1, 2.5, 5 and 10 for NTCDI molar composition), varying the feed ratio of NTCDI in random copolyimides, the memory devices exhibited the tunable electrical bistability from the volatile dynamic random access memory (DRAM) to nonvolatile write once read many (WORM) memory characteristics as the NTCDI composition increased. The OFF/ON electrical switching transition was mainly attributed to the charge transfer (CT) mechanism for charge separated high conductance. Also, the volatility of PI-NTCDIX device depended on the stability of CT complex. The long conjugation and high electron affinity of the NTCDI moiety stabilize the radical anion generated in the CT complex and prevented recombination of segregated radical species even through applying the high negative and positive voltage. The stability of the charge transfer between the donor and acceptor moieties could control the volatility of the memory devices.