| 摘要: | 在反式鈣鈦礦太陽能電池(Perovskite solar cells, PSC)中，一般使用PCBM作為電子傳遞層材料(Electron Transport Material, ETM)，但因PCBM不易純化，且製造成本高，因此近年來開始發展新的有機分子以作為反式鈣鈦礦太陽能電池元件之ETM。本研究以具有高熱穩定性、拉電子能力好的HAT (Hexaazatriphenylene)作為核心，利用其平面性及剛性結構有較好堆疊，電子遷移率較高，並在分子加入長碳鏈增加分子的溶解度，或在核心與碳鏈之間，插入一個硫原子，以增加硫-鉛、硫-碘的交互作用力來增加ETM和鈣鈦礦層的接觸。也將硫氧化成碸，或將thiophene改為thiazole，增強分子拉電子能力，並提高電子遷移率，合成出HAPN-1、HAPN-2、HAPN-3、HAPN-4、HAPN-5、HAPN-6六個化合物。實驗結果顯示，HAPN-1、HAPN-2、HAPN-3、HAPN-6之LUMO能階高於MAPbI3的LUMO能階，而HAPN-4、HAPN-5略高於MAPbI3的LUMO能階。由於碳鏈為支鏈或直鏈並不影響分子本質，因此電化學及UV-Vis吸收光譜的測試結果顯示，HAPN-2和HAPN-3的還原電位及吸光特性相似，HAPN-4與HAPN-5的光、電性質也相似，有強拉電子官能基的HAPN-4、HAPN-5、HAPN-6的最大吸收波長較HAPN-、HAPN-2、HAPN-3紅位移，還原電位也較高。由熱差示掃描分析(DSC)數據得知，只有碳鏈為直鏈的HAPN-3、HAPN-5分別在溫度110 oC及60 oC左右有一個吸熱峰產生，由TGA數據得知在此溫度範圍內，分子並不會分解。將五個材料製作為電子傳遞層組裝成元件，以長碳鏈為直鏈的HAPN-3、HAPN-5為電子傳遞層所組裝的元件比碳鏈為支鏈的HAPN-2、HAPN-4為電子傳遞層所組裝的元件光電轉換效率高。但由五個分子為ETM的元件光電轉換效率都不高，是由於分子能階和MAPbI3的能階不匹配，此外分子無法由旋轉塗佈法製備一個完整且連續的膜，因此電子無法順利傳遞至電極。其中HAPN-5因為sulfone官能基有增加電子遷移率的功能，以HAPN-5作為電子傳遞層的元件有光電轉換效率可達4.13%。;PCBM is generally used as an electron transport material (ETM) in Perovskite solar cells (PSC). However, PCBM is not easy to be purified therefore the cost is high. The developments of new organic ETM for inverted PSC have begun in recent years. In this study, five ETMs, HAPN-1, HAPN-2, HAPN-3, HAPN-4, HAPN-5, and HAPN-6 were synthesized for applying in PSCs. In these ETMs, HAT (Hexaazatriphenylene) with high thermal stability and good electron-trapping ability is used as the core for building the molecules. The planarity and rigid structure of HAT core can stack well in solid state to achieve high electron mobility. The long alkyl chains are added to the core to increase the solubility of the molecules. Furthermore inserting a sulfur atom between the core and the alkyl chain to increase the interaction between sulfur and lead or sulfur and iodine in perovskite to increase the contact between ETM and perovskite layer. Finally the sulfur on the alkyl chain was oxidized to form sulfone or the thiophene was replaced by thiazole to enhance the electrons attraction and increase the charge mobility of ETMs. The results show that the LUMO of HAPN-1, HAPN-2, HAPN-3, and HAPN-6 are higher than the LUMO of MAPbI3, while the LUMO of HAPN-4, HAPN-5 are slightly higher than the LUMO of MAPbI3. The electrochemical properties and absorbance characteristics of HAPN-2 and HAPN-3 are similar. HAPN-4 and HAPN-5 also have close optical and electrical properties. These findings suggest that the alkyl chain on the molecule did not affect the optic and electric properties of the molecules. HAPN-4, HAPN-5, and HAPN-6 with stronger electron withdrawing group have not only redshifted maxium absorption wavelength but also higher reduce potential. Differential scanning calorimetry (DSC) analysis revealed that only HAPN-3 and HAPN-5 which have linear alkyl chain have the endothermic peak at temperatures of 110 oC and 60 oC, respectively. In these temperature range, the molecules do not decompose from the TGA data. HAPN-3 and HAPN-5 with linear alkyl chain as the ETL for inverted PSC have higher photoelectric conversion efficiency (PCE) than HAPN-2 and HAPN-4 with branch alkyl chain respectively. However, the PCEs of the cells based on these five ETMs are all less than 5%. It may due to the unmatched LUMO level between MAPbI3 and ETM. The new ETM cannot form a continuous and dense film by spin coating may be another reason for the low photo-voltaic performance. The cell based on HAPN-5 ETL has the highest PCE of 4.13% among the five ETMs may the sulfone functional group increases the electron mobility. |
