探討注入電荷密度對於高分子太陽能電池及光感測器光電性質之影響

Abstract

本研究探討注入電荷密度對於高分子太陽能電池及光感測器光電性質的影響，並分析光感測器光電性質與負偏壓的關係。在模擬系統上選擇極具代表性之P3HT:PCBM系統，並結合易辛模型、光學轉換矩陣與動態蒙地卡羅方法三種模擬方法，針對太陽能電池之能量轉換效率以及光感測器之外部量子效率、暗電流密度以及載子傳遞時間等光電特性進行分析。在電荷注入密度對太陽能電池光電特性的影響上，我們發現陽極注入電洞在低外加電壓下皆被陽極提取，高外加電壓下少部分被陰極提取，所以電洞於陽極注入能障的降低使得JSC沒有明顯差異，VOC下降而FF上升，整體而言PCE呈下降趨勢。在光感測器上則發現當電洞注入能障極低時，在較厚的主動層下受陽極注入電洞停留數量較多的效應，外部量子效率下降、暗電流密度上升及電洞傳遞時間上升；在較薄主動層中則受大比率陰極注入電洞往陽極移動的影響，使外部量子效率及暗電流密度的上升。而在光感測器光電性質與負偏壓之變化趨勢的分析上，提升負偏壓使電洞(電子)往陽極(陰極)移動能力上升，在較厚的主動層中外部量子效率上升，載子傳遞時間下降。在較薄的主動層中受電極旁堆積電荷的吸引使其在高負偏壓下外部量子效率下降，載子傳遞時間上升並超越較厚的主動層。而隨厚度減少，外部量子效率深受光子吸收效率變化的影響，暗電流密度的變化則受陰極注入電洞密度的效應。本研究透過分析注入電荷密度與高分子太陽能電池及光感測器光電性質之間的關係，期許成果能提供實驗學者在研究上的參考依據，以促進此領域之發展。

In this study, we investigate the effects of the injection charge density on the photoelectric properties of polymer solar cells and photodetectors, besides that, the relationship between the photoelectric properties of photodetectors and reverse bias are also discussed. The iconic P3HT:PCBM system is chosen as our simulation object, and three different simulation method are combined, which includes Ising model, optical transfer matrix and kinetic Monte Carlo method. In particular, we evaluate the power conversion efficiency in polymer solar cells, external quantum efficiency, dark current density and carrier transit time in polymer photodetectors. In the part of polymer solar cells, we observe that most of the holes injected at anode are extracted by anode under low external voltage, and a small portion of holes injected at anode can travel to cathode under high external voltage. Thus decrease the hole injection barrier at anode make the open circuit voltage decreased and the fill factor increased with the short circuit current unchanged, which results in a decrease in the power conversion efficiency. For photodetectors under extremely low hole injection barrier at anode, the retention of holes injected at anode cause the decrease in EQE, and increases in both dark current density and hole transit time at thicker active layer thickness. For thinner active layer thickness, the increase of EQE and dark current density is caused by a large portion of the holes injected at cathode can migrate from cathode to anode. The effects of reverse bias to the photoelectric properties of polymer photodetectors is also discussed. By increasing reverse bias, the ability of hole(electron) hopping to anode(cathode) is enhanced. Which cause an increase in EQE and a decrease in carrier transit time at thicker active layer thickness, However, the charge accumulation beside electrodes make the thinner active layer thickness shows a decrease in EQE and an increase in carrier transit time, which is even higher compared to the thicker one. By decreasing the active layer thickness, EQE is strongly affected by photon absorption, and the change in dark current density is related to the injection hole density at cathode. Through the investigation of effects of the injection charge density on the photoelectric properties of polymer solar cells and photodetectors, we hope the results will provide references to experimental scholars for future research and promote the development of this field.