三元混摻系統有機太陽電池與異靛藍有機太陽電池

Abstract

本篇論文一共分為兩部分，第一部分是在二元混摻有機太陽能電池中，加入第三種聚合物，以期增強該光電元件的光捕獲範圍，或是產生高分子-富勒烯間的雙連續相，以提升其表面之相分離程度，達成改進效率之目的；第二部分是針對一種新穎異靛藍導電高分子，製備元件以進行效率最佳化的實驗。 在第一部分中，實驗的系統分別為P3HT:PC61BM以及PCPDTBT:PC61BM。P3HT，具有階段性退火後良好的結晶特性，PCPDTBT，為低能帶隙聚合物，在可見光譜波段有著更好的吸收性，實驗設計中我們在前述的兩個系統下，分別加入小比例的PCPDTBT及P3HT，使其成為三元混摻元件，最終最佳化的P3HT:PC61BM:PCPDTBT及PCPDTBT:PC61BM:P3HT系統相較於其在添加入第三種有機聚合物前，效率有10~20%的提升，最好的效率提升程度達到接近30%。 我們利用吸收光譜及外部量子效率量測分析比較之，結果發現P3HT:PC61BM:PCPDTBT系統在紅外光波長段，吸收度和量子效率相較於未加入PCPDTBT前有顯著之增加；而PCPDTBT:PC61BM:P3HT系統吸收光譜雖然在對應到P3HT的光吸收波段處有所增加，但外部量子效率是幾乎全波段性的上升而非只有局部提高。為了更進一步探討改進原因的差異性，我們使用原子力顯微鏡(AFM)觀察兩系統，發現P3HT:PC61BM:PCPDTBT系統如預期的有更分散、同質及平坦的表面，相較於P3HT:PC61BM，前者晶相聚集的程度縮小；而PCPDTBT:PC61BM:P3HT則比起PCPDTBT:PC61BM系統有著更明顯的結晶聚集、相分離現象，如此將有助於減少電子電洞對重組率，我們又針對此系統再作了穿透式電子顯微鏡(TEM)及掠角入射X光繞射分析(GIXRD)，而確認了PCPDTBT及PCBM的聚集度增加的現象及混摻系統中P3HT(100)結晶面訊號的出現。 基於增強可見光的光捕獲範圍及對表面形態改質兩種目的，在三種材料中原先僅二元混摻的製程，補入第三種聚合物，在製程最佳化後P3HT:PC61BM:PCPDTBT(CB+ 3% DIO)最高達到4.0%的效率，效率提升的主因來自長波長段光子吸收度的增加；PCPDTBT:PC61BM:P3HT (CB+ 3% DIO)則是3.3%，主要改進因素為薄膜表面相分離程度及聚合物聚集體大小變大，以上觀察到的種種現象與原本實驗設計的預期相吻合。 在論文的第二部分主題為異靛藍，一種新穎的導電高分子、良好的電子受體及低能帶隙材料，使用自己合成的六類具有不同側鏈的異靛藍導電高分子PC8Ie,PCeI8,PC8I8,PCeIe,PC12Ie,和PCeI12，和PC60BM混摻以製作元件，在製程中分別依序以添加劑的有無、不同的混合比例、及旋鍍轉速以逐步達成效率最佳化，由於異靛藍的側鍊長度及結構對應到電子予體PCBM濃度會有不同的傳導能力，為較關鍵之因素，因此我們將著重在混合比例項上作更多的參數調控，最後，與PCBM混摻後得到PCeIe:PCBM最佳效率4.0%，PCeI8 為3.6%，PC8I8 3.3%為幾組較佳的成果，而後量測了這一系列元件的吸收光譜、外部量子效率、及掠角入射X光繞射等物理性質分析，以提供為此新導電高分子合成的元件設計之製程參數作為參考。

This thesis contains two parts to investigate two new types of organic solar cell. The first one is about adding third polymer in the binary blend type of organic solar cells, thus it can enhance the light harvesting or generate more bi-continues phase that can achieve better phase separation in the active layer, finally accomplish the purpose of cell performance improvement; In the second part, we aim to investigate the structure effect of Isoindigo based conducting polymer on the performance of solar cell. This polymer exhibits low bandgap and is available from plant. We use it to make photovoltaic device and tune process conditions to optimize the performance of solar cell. In the first part, the experimental systems are poly(3-hexylthiophene) [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) and Poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl]]-C61-butyric acid methyl ester (PCPDTBT: PC61BM), P3HT has good crystalline phase after annealing while PCPDTBT has better absorption in the NIR spectra and high Voc. In our experimental design we add low weight ratio of PCPDTBT and P3HT respectively in the P3HT:PC61BM and PCPDTBT:PC61BM binary devices and they thus become ternary blend devices. We analyze the device by measuring the absorption spectra and external quantum efficiency (EQE), and find that both absorption intensity and external quantum efficiency of P3HT:PC61BM:PCPDTBT are obviously enhanced in the near infrared-visible spectrum compare to the P3HT:PC61BM binary system. In the case of PCPDTBT:PC61BM:P3HT, though the absorption intensity rises in the region related to the added P3HT, the enhancement of external quantum efficiency increases in almost from the UV-NIR region. For going into the details of this different causes of performance improvement, we utilize the atomic force microscopy (AFM) to observe those two systems, and we discover that the surface of P3HT:PC61BM:PCPDTBT smooth and better dispersed than that of P3HT:PC61BM, and the aggregations decreases; In contrast, PCPDTBT:PC61BM:P3HT ternary dissolved in CB+3% DiO has rougher surface, larger aggregation, thus contribute a decrease rate of charge recombination rate. Then we aim at PCPDTBT:PC61BM:P3HT system and further analyze it by transmission electron microscopy (TEM) and grazing incidence X-ray diffraction (GIXRD), thus acquire the PCPDTBT domain and PCBM clusters and detect the signal of P3HT (100) planes. For enhancing the light harvesting in visible spectrum and tuning the nano-morphology of thin film and binary system, we include third polymer in the original binary blend system, after optimizing the process, the best power conversion efficiency of P3HT:PC61BM:PCPDTBT system is slightly above 4.0%. It is about 10% higher than the highest one of P3HT:PC61BM: binary blend device which is due to the additional absorption in near infrared-visible region. The best PCEs value of PCPDTBT:PC61BM:P3HT dissolved in CB+ 3% DiO is 3.3%, which is also 10~20% higher than that of PCPDTBT:PC61BM. We can attribute the improvement to the morphology changes which result in moderate phase separation, so the above-mentioned phenomena confirm our prediction from the experimental design of this study. The second topic in the thesis is concentrated on the effect of Isoindigo device, a widely-used polymer in dye industry from one century ago, also a low band gap material, which is suitable for light harvesting donors for organic solar cells when blended with PCBM. We have evaluated four isoindigo polymers with different side-chain:PC8Ie, PCeI8, PC8I8,and PCeIe which are synthesized in our laboratory. In the attempt to optimize their device performance, we change the process by adding additive, different mixing ratio, and processing spin rate, because the structure of side chain (linear or branch), the length of side chain and the concentration of PCBM all can influence the charge mobility. Eventually, we obtain the best power conversion efficiency on different polymers: 4.0% in PCeIe:PCBM, 3.6% in PCeI8:PCBM, 3.3% in PC8I8:PCBM. Then, we measure and analyze the absorption spectra, external quantum efficiency, atomic force microscopy, and grazing incidence x-ray diffraction series of the active layer of these devices, thus we can provide useful information for manufacturing Isoindigo devices.