有機發光二極體以及鈣鈦礦太陽能電池的電性以及光學元件模擬

Abstract

本論文使用了實驗室自主開發的Poisson & drift-diffusion軟體(DDCC)來探討有機發光二極體以及鈣鈦礦太陽能電池的元件表現，並且針對元件的特性進行模擬上的優化。例如，在有機發光二極體以及鈣鈦礦太陽能電池中使用了高斯態密度以及Poole-Frenkel場效載子遷移率模型來模擬載子在有機主動層以及傳輸層的傳輸情形、透過求解激子擴散模型來探討激子在有機發光二極體中對於效率的影響以及優化以及透過time-dependent離子擴散模型探討鈣鈦礦太陽能電池中由移動離子造成的遲滯效應的影響。各章節的細節如下：(1) 以及探討在有機主客混合系統中的載子遷移率變化模型，電子電洞在發光層中平衡分佈是各種有機發光二極體中的重要課題，然而目前大部分高效的有機發光二極體需要藉由摻雜主客體有機材料來增加發光效率，許多研究指出有機系統摻雜後的載子遷移率變化是非線性的變化，因此這讓載子平衡在設計上變成一件困難的事情。我們利用上述提到的求解器並且配合易辛模型來展示主客體材料中載子遷移的變化，為了驗證求解器的正確性，我們分別製備了不同濃度的單一電子/電洞元件以及參考文獻中三種不同的有機主客體混合系統的量測資料來確認求解器的正確性和可靠度。驗證過後則透過模擬結果可以發現產生這種非線性變化的原因為在客體材料濃度較低時，客體材料在系統中扮演了類似缺陷陷阱的角色，由於濃度太低以及主客材料能量差過大，因此將會導致系統大部分載子被局域化至客體材料且系統整體的移動性載子數量大量下降，而造成載子遷移率的大幅下降。而在摻雜濃度漸漸上升的過程中，對於載子而言，客體材料會漸漸形成通道的角色因而使載子能夠在這些低能態的通道上傳輸，因此載子遷移率會漸漸上升至接近客體材料本身的載子遷移率。(2) 探討TTF-OLEDs的電性模擬，在這此工作中，該求解器用於探討TTF 和hyper-TTF-OLEDs的電性差異。 並且能夠用於解釋hyper-TTF-OLEDs的機制並且分析不同激子機制造成效率的耗損。透過模擬結果可以將內量子效率由23%提升至35%。 (3) 並且透過時變離子遷移模型，能夠探討由離子引起的鈣鈦礦太陽能電池中的電流電壓遲滯效應，並且透過模擬結果可以發現造成遲滯效應最關鍵的因素為鈣鈦礦材料中的內建電場，並且透過模擬以及實驗對比展示了在不同電壓掃描速率下的非線性遲滯曲線。此外，透過模擬可以發現影響遲滯程度的關鍵在於鈣鈦礦材料的解離程度、 鈣鈦礦晶體的品質以及載子傳輸層的材料。其中載子傳輸層的影響來自於所選材料的介電常數，選擇介電常數較低的材料作為載子傳輸層，由於能夠將整體的電壓較大程度的分壓至傳輸層，進而讓鈣鈦礦材料層的分壓較低而降低離子帶來的遲滯效應。

In this thesis, an in-house Poisson & drift-diffusion solver (DDCC) is implemented to calculate the performances of organic light-emitting diodes (OLEDs) and perovskite solar cells (PSCs) and optimize the characteristics of the device. The multi-Gaussian shape density of state and Poole-Frenkel field-dependent mobility model are introduced to describe the carrier distribution and transport mechanism in organic materials. Moreover, an advanced exciton diffusion model considering most exciton behavior and the interaction of singlet and triplet exciton is developed to demonstrate the radiative recombination mechanism. This exciton model can be utilized for fluorescent, phosphorescent (Ph), TADF, and TTF-OLEDs. Also, this solver can couple with optical modeling program to calculate the optical field of PSCs to demonstrate the performance of PSCs and utilize the time-dependent ion migration model to discuss the effect of mobile ions on the hysteresis phenomenon. The details of all work are shown in the following: (1) Discussing the carrier mobility change in the organic-based host-guest system. The balance of electron and hole distribution in EML is a crucial issue in optimizing the performance of OLEDs. Doping is a standard method to achieve the high performance of OLEDs. However, many studies have shown that the carrier change is non-linear and unpredictable for the host-guest system, making the design of carrier balance tough to achieve. We applied this solver, Ising model, and SCLC model to demonstrate the carrier mobility under different doping concentrations. Also, this model is verified by different electron- and hole-only devices prepared by ourselves and other measurement data from previous studies. Modeling results show that the reason for this non-linear change is that the guest materials act as a trap state when the doping concentration is low. Due to the difference in host-guest energy being too high, most carriers would be localized in the guest materials, resulting in the number of mobile carriers decreasing significantly and the mobility declines simultaneously. However, the number of mobile carriers would grow when the doping concentration increases. The guest materials would cluster together gradually and form the channel in the system, which causes the mobility increases smoothly to approach the mobility of pure guest material. (2) Discussing on modeling of TTF-OLEDs. In this work, this solver is applied to demonstrate the characteristics of TTF- and hyper-TTF-OLEDs. Also, This solver can be used to explain the mechanism of hyper-TTF-OLEDs and analysis the loss from different exciton mechanisms. Furthermore, we can do further optimization for hyper-TTF-OLEDs to achieve an internal quantum efficiency increase of 23% (from 29% to 35%). (3) Moreover, a time-dependent ion migration model coupled with a Poisson-DD solver is presented in this thesis to demonstrate the hysteresis of PSCs. Modeling results show that the crucial issue in hysteresis is the built-in electric field. Also, three different factors of PSCs (carrier lifetime, scan rates, and dielectric constant of transport layer) were demonstrated to understand hysteresis. Finally, we found that choosing a transport layer with a lower dielectric constant can decline the hysteresis of PSCs.