檢視異質接面高分子太陽能電池光電轉換效率之關鍵影響因素

Abstract

本研究探討異質接面高分子太陽能電池中主動層厚度、分離區塊尺寸以及電荷遷移率對於光電轉換效率與各項光電性質的影響，藉由系統性的調整各項變因分析何者為電池效能表現的關鍵影響因素。我們共結合光學轉換矩陣、易辛模型與動態蒙地卡羅方法三種模擬，並選用極具代表性的P3HT:PCBM 混摻系統進行模擬，並將模擬結果與本實驗室中以 PffBT4T-2OD:PCBM 混摻系統進行模擬之結果進行比較，探討不同電子予體材料之混摻系統受到上述三種變因之影響差異。 首先，我們從實驗文獻決定模擬中的設定參數並利用多次測試比對調整部分待定的參數，以確保模擬結果足以反應真實實驗之趨勢。在對於主動層厚度的調控中，我們發現主動層厚度以及入射光線的干涉作用對於光子吸收效率有極為關鍵之影響，雖然光子吸收效率大致隨厚度增加而上升，但亦需衡量厚度增加對電荷傳遞之負面效應；而主動層在分離區塊尺寸約 15 nm 時有最佳的光電性質表現，除了擁有較高的激子解離效率，也具有最低的電荷再結合比例，此結果與主動層形態中的材料孤島有極大的關聯；本研究中電荷遷移率的提升對光電性質極具助益，值得注意的是此結果與一般追求兩種電荷遷移率平衡的觀念有所出入。在兩種混摻系統的比較中，我們發現材料選擇對光子吸收效率與電荷傳遞能力仍具有絕對的影響，因此除了主動層厚度、分離區塊尺寸以及電荷遷移率三項變因，混摻系統材料選擇更是具有不可輕忽的影響。藉由本研究中對於檢視異質接面高分子太陽能電池光電轉換效率之關鍵影響因素的討論，期望可以提供未來之實驗學者在高分子太陽能電池設計與製作上的建議與方向。

Impact of active layer thickness, domain size and charge mobility in bulk heterojunction polymer solar cell on power conversion efficiency(PCE) and opto-electrical properties has been studied in this work. Key factors in the efficiency are investigated by systematically manipulating these variables. Our multiscale simulation consists of optical transfer matrix, Ising model and kinetic Monte Carlo method, and P3HT:PCBM active layer is chosen as our simulating subject. The results are compared with PffBT4T-2OD:PCBM active layer to demonstrate the different effects of these variables. Firstly, by setting the input parameters according to experimental reference or fitting with experimental results, we aim at examining the influence of the three variables with caution. In the variation of active layer thickness, photon absorption is strongly related to thickness. Though thicker active layer usually absorbs more photons, the charges may suffer from long-distance diffusing to electrodes. Besides, domain size of active layer can also affect the performance of solar cell. It is found that morphology with domain size of 15 nm reaches higher efficiency due to its high exciton dissociation efficiency and low charge recombination ratio. Nevertheless, the existence of isolated sites also plays a crucial role in it. Additionally, the result in varying charge mobility shows that the efficiency can increase with higher charge mobility regardless of unbalanced hole and electron mobility. In the comparison of two different electron donor materials, all three variables show similar trends and the ability of light absorption is still the decisive factor in efficiency. By examining the key factors in the efficiency of bulk heterojunction polymer solar cell, we hope these contributions can provide concrete suggestions to scientist on designing and fabricating polymer solar cell.