| 摘要: | 本研究以有機發光二極體(Organic Light-Emitting Diode, OLED)為研究主軸，系統性探討電子注入層、電洞阻擋層、電洞調控層以及主體/客體材料選擇對元件電性與發光效率之影響。研究中採用Super Yellow(SY)、PFO、CBP以及一系列 D2-nPh材料作為發光或主體材料，並透過元件結構與材料參數之調控，逐步建立高效率OLED元件架構。
首先，比較不同電子注入層材料之影響，結果顯示相較於LiF，Li₂CO₃可有效改善電子注入行為，使元件展現較佳之操作電壓與發光效率，因而被選定為後續元件之電子注入層。接著，探討不同電洞阻擋層(Hole Blocking Layer, HBL)材料對元件效能之影響，比較TmPyPB、BCP與BP4mPy後發現，TmPyPB能有效侷限電子並改善載子平衡，使SY與PFO元件之外部量子效率(External Quantum Efficiency, EQE)顯著提升，並成為後續研究中主要採用之HBL材料。
在完成電子注入層與電洞阻擋層之篩選後，進一步引入聚乙烯咔唑(poly(9-vinylcarbazole), PVK)作為電洞調控層。PVK之LUMO能階可有效阻擋電子穿越主動層，而其HOMO能階亦可與CBP與PFO形成較佳之能階匹配，使元件整體載子平衡與發光效率獲得改善。隨後，在相同且已最佳化之元件架構下，比較不同主體材料之表現，結果顯示雖然SY具備較高之發光效率，但其與PVK之能階匹配較差；相對而言，D2-4Ph在效率與操作電壓上展現出較佳之整體穩定性。
為進一步分析D2-nPh系列材料之差異，本研究製作單電洞元件，並以空間電荷限制電流(Space-Charge-Limited Current, SCLC)模型分析其電洞遷移率。結果顯示 D2-4Ph具有最高之電洞遷移率，且其OLED元件亦表現出相對較佳之發光效率。
在主體/客體摻雜元件方面，本研究將2DIndFL-PT、DIndFL-2-BTAQ與 DIndFL-TTp-Tp-1-C6BTABTD等客體材料分別摻入D2-4Ph、CBP、PFO與SY主體中，探討摻雜濃度對元件效能之影響。結果顯示，適當摻雜可有效提升元件EQE，而過高濃度則因能量轉移效率下降與非輻射淬滅效應增加，導致效率降低。特別是在SY主體中，摻雜近紅外客體材料後之EQE普遍低於純SY元件，主要歸因於主體發光光譜與客體吸收光譜重疊不足，使能量轉移效率受限。
最後，本研究以D2-4Ph為主體材料，透過摻雜SY並調控其濃度，成功實現白光OLED元件。結果顯示，雖然較高SY濃度可提升發光效率，但在色溫表現上，低至中等濃度之SY摻雜更接近理想白光範圍，顯示在效率與色度之間需取得適當平衡。
綜合上述研究結果，本研究證實透過電子注入層與電洞阻擋層之適當選擇、PVK電洞調控層之引入、主體/客體材料能階與光譜匹配，以及材料載子遷移率之最佳化，可有效提升OLED元件之發光效率與電性表現，對未來高效率有機發光材料與元件設計具有重要參考價值。
;This study focuses on organic light-emitting diodes (OLEDs) and systematically investigates the effects of electron injection layers, hole blocking layers (HBLs), hole modulation layers, and host–guest material selection on device electrical characteristics and emission efficiency. Super Yellow (SY), PFO, CBP, and a series of D2-nPh materials were employed as emissive or host materials. Through step-by-step optimization of device architecture and material parameters, high-performance OLED structures were established.
First, the influence of different electron injection layers was examined. Compared with LiF, Li₂CO₃ exhibited superior electron injection behavior, leading to lower operating voltage and improved device efficiency. Consequently, Li₂CO₃ was selected as the electron injection layer for subsequent devices. The effects of various hole blocking layer materials, including TmPyPB, BCP, and BP4mPy, were then evaluated. Among them, TmPyPB effectively confined electrons and improved carrier balance, resulting in significantly enhanced external quantum efficiency (EQE) in both SY- and PFO-based devices, and was therefore adopted in later studies.
After optimizing the electron injection and hole blocking layers, poly(9-vinylcarbazole) (PVK) was introduced as a hole modulation layer. The LUMO level of PVK effectively suppresses electron leakage through the emissive layer, while its HOMO level provides favorable energy level alignment with CBP and PFO, leading to improved carrier balance and device performance. Under the same optimized device architecture, different host materials were then compared. Although SY exhibited high emission efficiency, its energy level alignment with PVK was less favorable. In contrast, D2-4Ph demonstrated more stable performance with a favorable balance between efficiency and operating voltage.
To further elucidate the intrinsic material properties of the D2 series, hole-only devices were fabricated and analyzed using the space-charge-limited current (SCLC) model. Among the D2-nPh materials, D2-4Ph exhibited the highest zero-field hole mobility, which correlated well with its superior OLED performance.
In the host–guest doping studies, 2DIndFL-PT, DIndFL-2-BTAQ, and DIndFL-TTp-Tp-1-C6BTABTD were incorporated into D2-4Ph, CBP, PFO, and SY host materials to investigate the influence of doping concentration on device performance. The results show that appropriate guest doping significantly enhances EQE, while excessive doping leads to reduced efficiency due to decreased energy transfer efficiency and increased non-radiative quenching. In particular, SY-based devices doped with near-infrared emitters exhibited lower EQE than pristine SY devices, primarily due to insufficient spectral overlap between the host emission and guest absorption, limiting energy transfer efficiency.
Finally, white OLEDs were realized using D2-4Ph as the host material with SY as a complementary emitter. By tuning the SY doping concentration, both emission efficiency and correlated color temperature (CCT) could be modulated. Although higher SY concentrations yielded higher EQE, lower to moderate doping concentrations provided CCT values closer to ideal white light, indicating a trade-off between efficiency and color quality.
Overall, this study demonstrates that proper selection of electron injection layers and hole blocking layers, introduction of PVK as a hole modulation layer, optimization of host–guest energy level alignment and spectral overlap, and enhancement of charge carrier mobility are critical factors for improving OLED efficiency and electrical performance. These findings provide valuable insights for the design of high-efficiency organic emissive materials and OLED devices. |
