有機高分子與無機混成太陽能電池在倒置結構下研究

Abstract

有機太陽能電池具有質輕、可撓曲且在大面積下製作可以有較低的成本，近年來引起廣大的注意。在本論文中，我們使用PV2000做為倒置結構元件的主動層，比起P3HT/PCBM系統能提供較大的開路電壓。首先我們嘗試使用後退火處理來改善元件效率，藉由熱引發主動層型態的改善以及界面缺陷的修補，在這邊我們能發現後退火處理對於此元件的重要性。接著我們利用溶液製程的方式將金屬氧化物氧化鎳（稱作電子阻擋層/電洞傳輸層）旋轉塗佈在主動層上面，利用其較高的最低分子未佔據軌域，來阻擋電子直接傳輸到陽極與收集到此處的電洞進行復合，減少元件的漏電流產生增加元件的填充因子，進而提升反向結構元件之效率。當二氧化鈦奈米柱添加後，光吸收以及光電流的改善是顯而易見的，我們可以歸納出以下功能。第ㄧ,使主動層變厚從200nm提升至280nm，因此增加光吸收，使得光電流能有效提升。第二，其奈米結構型態能提供主動層與無機層間更大的接觸面積，能在有機層內幫助收集電子，並藉由高載子遷移率的無機通道傳送至ITO電極。第三，此二氧化鈦奈米柱可以降低激子復合的機率，幫助激子分離。因此元件效率能有效的被改善至5.61%。在論文的最後，我們將工研院研發的低能隙材料(ITRI P47:PC70BM)應用在我們倒置結構太陽能電池上，藉由調整主動層厚度改善光吸收之外，同時配合使用NiO層介於主動層以及銀電極之間做為電子阻擋層，阻擋電子傳送到電極銀處與電洞復合，有效抑制漏電流。

Organic photovoltaic devices are very attractive for their advantages of flexibility, light-weight, and large-area production at a dramatically low cost. In this study, the PV2000 material is used as a photoactive layer, which has a larger relative energy difference between the HOMO level of the electron-donating polymer and the LUMO level of the electron acceptor (energy difference ~1.7 eV) as compared to the standard P3HT:PCBM system, thereby leading to a larger VOC. The better contact in the interface is achieved by the post-annealing process, which corrects the defects between electrode and polymer layer interface. Moreover, the thermally induced morphology modification, crystallization and improved interfacial transportation, thereby leading to better charge collection and reduced series resistance. These results show that the process of post-annealing is very important for our PV2000 inverted device. We used solution process to replace deposition to spin NiO layer on active layer. NiO layer acts as an interfacial electron-blocking layer/hole-transporting layer (EBL/HTL). Utilizing its higher LUMO (lowest unoccupied molecular orbital) could block electron leakage to anode to recombine with hole. The leakage current is reduced to improve the power conversion efficiency of inverted structure devices. When the TiO2 nanorods are introduced, an improvement of light harvest and photocurrent is achieved due to several factors. First, the photoactive layer is thickened and the light path is increased to have more light absorption. Second, the morphology is modified to provide the photoactive layer and inorganic layer a larger contact area for efficient charge collection. Third, the TiO2 nanorods enhance the photoluminescence quenching, indicating improved electron-hole dissociation. In this way, the high PCE of 5.61% from inverted PSCs is achieved. In the second part of this work, our investigation apply the low band gap material (ITRI P47:PC70BM) as the photoactive layer. The light harvest is improved by adjusting the thickness of photoactive layer. In addition, we introduce the solution-process NiO layer between photoactive layer and silver as an electron blocking layer, therefore, the electron is forced to move toward the ITO electrodes, increasing the selectivity of the charge carriers and the shunt resistance of the photovoltaic cell.