dc.description.abstract | 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. | en_US |