本論文中，我們利用阻抗分析頻譜分析有機太陽能電池，藉由阻抗分析儀量測有機太陽能電池，並將所測得之阻抗訊號代入元件之等效模擬電路，透過等效電路中之電阻及電容等模擬元件之數值，分析有機太陽能電池中各層之物性及電性。
首先，本研究先針對近期較常被應用於高效率有機太陽能電池材料添加劑-1,8-二碘辛烷(1,8-diiodooctane, DIO)-對於有機太陽能電池元件中主動層電性之影響。透過阻抗分析儀可將主動層分析成一電阻與一電容之並聯電路，發現當DIO添加入主動層時，模擬出之電阻下降(CB:773.89526.46 Ω; DCB:671.65542.37 Ω)且電容上升(CB: 7.6914 nF; DCB: 9.3713.4 nF)，並透過電阻及電容之變化可間接量化出有機施體材料與有機受體材料於主動層內之接面關係。此外，本項研究也發現透過阻抗分析儀模擬出之電阻與電容之乘積常數大小將直接關係到元件表現之優劣(6.29 μs 4.2 %; 7.27 μs 6.21 %)。本研究也透過不同主動層厚度驗證阻抗分析頻譜與等效電路之關係，並調變DIO於主動層內之濃度驗證施體材料與受體材料間之接面關係。
針對含DIO之有機太陽能電池中，本研究也進一步研究其主動層於熱效應上對於元件效率與主動層之分子排列形態之關係，發現熱效應只針對有添加DIO之主動層產生退化之效果，並藉由原子力顯微鏡量測其主動層分子排列形態之變化，再利用阻抗分析儀探討其主動層之分子排列形態與其模擬電阻與電容之關係，發現由於小分子因受熱而結晶，導致施體材料與受體材料之接面面積下降，因此主動層之電阻上升(540.48 692.81 Ω)而電容下降(17.4610.43 nF)。
由於本文利用雷射退火與熱退火有效改善有機太陽能電池之特性(從3.54%提升至4.01%)，因此本研究也利用阻抗分析頻譜，以探討雷射退火與熱退火改變之物性變化與其施體材料與受體材料間之接面關係，發現未退火、單純熱退火與雷射及熱共退火之主動層電阻/電容分別為573.04 Ω / 25.07 nF、541.98 Ω / 31.48 nF與521.4 Ω / 34.75 nF，藉由模擬電阻與電容之變化進而推論元件分子排列之特性，並發現當施體材料與受體材料之接面固定時，有機材料本身之結晶將可決定元件之主要特性。
針對有機太陽能電池之效率增進，本文也利用摻雜有機磷光材料至主動層中，除了有效提升元件特性從(6.15%提升至7.08%)，本研究也利用阻抗分析頻譜探討其摻雜與電性之關係，並發現較長之激子生命週期(67.28986.765 ps)確實提升元件之短路電流(10.4412.4 mA/cm2)，且也對應到較高之模擬電阻電容乘積常數(35.0840.07 μs)。此部分也比較不同退火參數於摻雜有機磷光材料之主動層之影響，對於有機磷光材料於主動層內之變化與其對應之元件特性與模擬之電阻與電容之差異進行更深一層之探討。
最後，除了有機太陽能電池之主動層，本研究也利用阻抗分析儀探討主動層與電極接面之關係，發現接面能障越大(-1.10.30.7 eV)，則接面電阻越大(42.1146.32193.21 Ω)且電容越小(1.582.563.67 nF)。此項研究成功建立出主動層與電極接面之能障變化與模擬電阻電容乘積常數之線性關係，並透過該關係間接定義出載子傳輸層於電極與主動層接面形成之有效功函數。本項研究也透過調變載子傳輸層厚度及表面粗糙度，發現當載子傳輸層表面粗糙度越小(7.967.6065.13 nm)，接面面積相對越小而導致接面電阻上升(44.5147.7355.6962.88 Ω)而電容下降(16.514.2119.45 nF)，以分析其接面模擬電阻與電容之變化。
對於有機太陽能電池之探討，物性之相關分析已乘載於許多文獻中，然而卻仍然有許多與其電性之連結尚未建立，而本論文之研究有效地利用電性的方式對有機太陽能電池進行探討，透過其模擬電路中之模擬元件可間接量化其施體材料與受體材料於主動層內之排列形態與相互關係，且可用以分析各種針對主動層變化之製程。此外，本研究也透過阻抗分析頻譜探討主動層與電極之接面關係，量化出其接面特性，著實為一快速有有效之分析方式。

This dissertation utilizes impedance spectroscopy (IS) to analyze organic photovoltaics (OPVs). The OPV devices are simply simulated to a circuit model, and the value of each element in the model is defined by fitting the impedance spectra. With the value of each element, the OPV device can be studied separately in terms of active layer part and interlayer part. We can derive more electrical information from the value of the separated elements which mainly corresponds to the physical difference from the active layer or the interlayer.
1, 8-Diiodooctane (DIO) has been known for its role of improving the polymer morphology and enhancing performance of polymer bulk heterojunction (BHJ) solar cell. First, the impedance spectroscopy was used to investigate the interface of poly(4,8-bis-alkyloxybenzo(1,2-b:4,5-b’)dithiophene-2,6-diyl-alt- (alkyl thieno(3,4-b) thiophene-2-carboxylate)-2,6-diyl) (PBDTTT-C):PC70BM in BHJ with DIO as additive. Based on our results, we were able to simulate the device into an equivalent circuit model, which allows us to conveniently analyze the organic/organic interfacial contact in the OPV device. Thus, we demonstrate that the impedance spectroscopy can an effective approach in characterizing the donor/acceptor interfaces, such that a direct correlation can be established between the morphology and the device performance of BHJ devices.
Besides, most photovoltaics operate at high temperature under sunlight. In this work, the thermal instability of DIO-based high-efficiency BHJ OPVs is studied. The BHJ layers were heated to various temperatures to investigate the changes in their physical properties using atomic force microscopy phase images. The mobilities of the carriers were characterized at various temperatures using the space-charge-limited current method, and the carrier lifetime was calculated by applying impedance spectroscopy to the simulated equivalent circuit of the OPV devices.
We also propose an approach for improving the performance of poly(3-hexylthiophen) (P3HT)-based OPVs. P3HT-based BHJ film can absorb the energy from 532-nm laser light and be transformed into favorable morphology. A combination of traditional thermal annealing and laser annealing improved device performance, with a slight increase in fill factor and a significant improvement in short-circuit current density. Better crystallization and a higher degree of molecular order in the thermal/laser co-annealed P3HT-based BHJ film were observed through X-ray diffraction and Raman spectroscopy. In this work, the BHJ layer was also analyzed via IS to investigate the interfacial property of donor and accepter materials. The simulated elements represent to the BHJ layer demonstrate different result from the DIO-based OPVs under annealing process.
To improve the OPV device performance, we also doped phosphorescent material tris(phenylpyrazole)iridium (Ir(ppz)3) into the BHJ layer of a P3HT and indene-C60 bisadduct (ICBA) blend to form more excitons at the triplet state. Triplet-state excitons have longer lifetimes than those of singlet-state excitons. Surface phase separation was determined via atomic force microscopy and the vertical distribution of various molecules was analyzed via secondary ion mass spectroscopy. Several annealing processes were applied to the BHJ layer doped with Ir(ppz)3 to investigate the thermal stability of the film. The exciton lifetime in the BHJ film was characterized using femtosecond time-reserved photoluminescence. The BHJ layer doping with Ir(ppz)3 was analyzed through IS as well. The variation on the elements which represent to the BHJ layer is different from the one as analyzed in previous works. The physical meanings on the Ir(ppz)3-doped BHJ film was well studied.
At last, we investigate the interface between the active layer and contacts in OPVs since the contact materials strongly affect the energy barrier at the interfaces. The interfacial characteristics are simply defined as a resistance-capacitance (R-C) shunt pair and extracted by fitting the impedance spectra to the equivalent circuit model. A change in the energy barrier is found to affect the values of R and C at the interface and the carrier transition time. In addition, the effect of electron buffer layer (TiO2) thickness on the interfacial characteristics is analyzed using impedance spectroscopy. The interfacial area between the hole buffer layer (MoO3) and the active layer affects the values of R and C at the interface.
We deliver a fast and simple way to investigate the OPV devices not only on BHJ layer but also on interfaces between BHJ layer and electrodes via IS. It is a method to combine the physical property and current density-voltage (J-V) characteristics of OPV devices together. By analyzing the OPV devices through IS, more unclear physical meanings in BHJ or interface between contact and BHJ layer are explainable.

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