形貌可控的生物高分子嵌入有機染料應用於增強型光學有機場效應電晶體記憶體裝置

Abstract

有機場效電晶體中的光記憶元件因其可撓性基材相容性、低功耗操作與製程簡易性，已成為新世代非揮發性記憶體的潛力候選者。在追求性能提升與節能寫入機制的過程中，採用光致閘控策略的研究逐漸受到重視，特別是基於光敏電荷捕捉層與激子行為的機制，例如三重態–三重態湮滅與磷光發光。而在眾多候選機制中，放大自發輻射因具備快速的光響應與低激發能量門檻，成為光記憶應用中備受關注的選項之一。 在第二章中，本論文探討了將具備放大自發輻射特性的有機雷射染料 PM597與醋酸纖維素結合，透過電紡與薄膜製程構築浮動閘極電荷捕捉層，應用於有機場效電晶體光記憶架構中。為系統性分析奈米尺度形貌、光散射行為、放大自發輻射產生與電荷儲存效率間的關聯，本研究發展出四種製備策略：混合式薄膜、雙層薄膜、混合式奈米纖維與雙步驟奈米纖維。其中，雙步驟奈米纖維系統展現出最低的放大自發輻射門檻（4.68 ± 0.46 μJ）、更優異的激子動態與均勻的染料分布，進而大幅提升記憶體效能，包含記憶電流比超過10⁵、保持時間超過10,000秒，以及在低能量光照條件下仍具良好的寫入與擦除循環穩定性。這些結果強調了放大自發輻射與奈米結構形貌之間的緊密關聯，並指出透過光子設計來調控光電特性為一具潛力的策略。 延續上述成果，第三章進一步探討了去除光散射增益後，放大自發輻射對記憶性能之內在影響。為此，研究採用雙層膜系統，結合幾丁聚醣與供體–受體–供體結構染料2OMe-DFL-Tr2，該染料已在先前文獻中證實即使在固態薄膜中亦可展現放大自發輻射行為。此外，本章也著重探討以天然高分子作為電荷捕捉層，用以細緻調控界面特性。透過改變醋酸濃度，成功調控幾丁聚醣的組裝形貌，由無定形網狀結構轉變為短棒狀結構，並經由原子力顯微鏡與傅立葉轉換紅外光譜來驗證。此一形貌轉變顯著影響了光學發光行為與界面電荷捕捉特性，採用短棒狀幾丁聚醣的元件展現出更明顯的藍位移光致螢光與更寬的記憶窗口。此外，酸誘導的形貌控制也對染料聚集行為的抑制發揮關鍵作用。在最佳化的製程與後處理條件下，染料聚集被有效抑制，從紫外–可見螢光光譜的藍位移中可從旁佐證。此聚集抑制效果不僅提升了發光純度，也增強了在有機–有機界面上的激子解離效率，最終提升了光記憶元件的整體效能，包含記憶電流比超過104、穩定保持時間超過10,000秒，以及超過20次的穩定寫入–擦除循環特性。 總體而言，本研究顯示透過光增益工程與界面形貌調控的雙重設計，都可應用在提升光記憶元件的表現，為未來高性能光電記憶系統提供了有價值的設計策略。

Organic field-effect transistor (OFET) photonic memory devices have emerged as promising candidates for next-generation nonvolatile memory, owing to their compatibility with flexible substrates, low power operation, and ease of fabrication. In the pursuit of enhanced performance and energy-efficient programming mechanisms, photogating strategies employing photoactive electrets and exciton-based processes—such as triplet–triplet annihilation (TTA) and phosphorescence—have attracted growing interest. Among these, amplified spontaneous emission (ASE) has emerged as another promising mechanism, offering rapid optical response and low excitation thresholds, making it particularly attractive for photonic memory applications. In chapter 2, this thesis investigates the integration of pyrromethene 597 (PM597), an organic laser dye known for its ASE characteristics, with cellulose acetate (CA) via electrospinning and film-based methods to form the floating-gate electret in OFET photonic memory structures. Four fabrication strategies—including mixed composite film, bilayer film, mixed composite fibers, and two-step fibers—were developed to examine the relationship between nanoscale morphology, scattering behavior, ASE generation, and charge storage efficiency. Among these, the two-step fiber configuration exhibited the lowest ASE threshold (4.68 ± 0.46 μJ), enhanced exciton dynamics, and a uniform dye distribution, leading to significantly improved memory performance with a memory ratio exceeding 10⁵, stable retention beyond 10,000 seconds, and durable cycling characteristics under low-energy light exposure. These findings highlight the strong correlation between morphology-controlled ASE and photomemory enhancement, offering a new perspective for tailoring optoelectronic properties through photonic design. Building on this, Chapter 3 further investigates photomemory modulation strategies by eliminating the scattering-induced optical gain and focusing instead on the intrinsic impact of ASE on OFET memory performance. To this end, a bilayer film system was employed, incorporating chitosan and donor–acceptor–donor structured dye, 2OMe-DFL-Tr2, known for its capability to exhibit ASE even in the solid-state films as reported in prior studies. In addition, this chapter explores the use of biopolymer-based electrets for fine-tuning interfacial properties in bilayer OFET memory devices. By varying the acetic acid concentration, the supramolecular assembly of chitosan was modulated from amorphous networks to rod-like domains, as verified by atomic force microscopy (AFM) and Fourier-transform infrared spectroscopy (FTIR). These morphological transitions significantly influenced the optical emission behavior and interfacial charge trapping, with devices utilizing the short-rod chitosan morphology exhibiting more prominent blue-shifted photoluminescence and enhanced memory windows. Furthermore, the acid-mediated morphology control also played a critical role in regulating the aggregation of dye molecules. Under carefully designed process and post-treatment conditions, dye aggregation was effectively suppressed, as evidenced by a noticeable PL blue-shift in the UV–vis spectra. This suppression not only improved the optical emission purity but also enhanced exciton dissociation efficiency at the organic–organic interface, collectively contributing to improved photomemory performance, exceeding 104, stable retention beyond 10,000 seconds, and durable cycling characteristics over 20 cycles. Overall, this work demonstrates how both optical gain engineering and interfacial morphology tuning can synergistically enhance the performance of photonic OFET memories, providing valuable design strategies for advanced optoelectronic memory systems.