Defect Passivation by Amide-Based Hole-Transporting Interfacial Layer Enhanced Perovskite Grain Growth for Efficient p–i–n Perovskite Solar Cells

• Published in: ACS applied materials & interfaces Vol. 11; no. 43; pp. 40050 - 40061
• Main Authors: Wang, Shin-Yu, Chen, Chih-Ping, Chung, Chung-Lin, Hsu, Chun-Wen, Hsu, Hsiang-Lin, Wu, Ting-Hsuan, Zhuang, Jia-Ying, Chang, Chia-Jui, Chen, Hao Ming, Chang, Yuan Jay
• Format: Journal Article
• Language: English
• Published: American Chemical Society 30.10.2019
• Subjects: crystal structure; density functional theory; indium; indium tin oxide; ions; lead; Lewis bases; moieties; nickel; photoluminescence; solar cells; thiophene; tin; amide-based hole transporting material; p−i−n type perovskite solar cells; interfacial layer; perovskite solar cells
• ISSN: 1944-8244; 1944-8252; 1944-8252
• DOI: 10.1021/acsami.9b13952

In this study, we synthesized four acceptor–donor–acceptor type hole-transporting materials (HTMs) of SY1–SY4 for an HTMs/interfacial layer with carbazole as the core moiety and ester/amide as the acceptor unit. These HTMs contain 4-hexyloxyphenyl substituents on the carbazole N atom, with extended π-conjugation achieved through phenylene and thiophene units at the 3,6-positions of the carbazole. When using amide-based HTMs SY2 as a dopant-free HTM in a p–i–n perovskite solar cell (PSC), we achieved a power conversion efficiency (PCE) of 13.59% under AM 1.5G conditions (100 mW cm–2); this PCE was comparable with that obtained when using PEDOT:PSS as the HTM (12.33%). Amide-based SY2 and SY4 HTMs showed a larger perovskite grain than SY1 and SY3 because of the passivation of traps/defects at the grain boundaries and stronger interaction with the perovskite layer. In further investigation, we demonstrated highly efficient and stable PSCs when using the dopant-free p–i–n device structure indium tin oxide/NiO x /interfacial layer (SY-HTMs)/perovskite/PC61BM/BCP/Ag. The interfacial layer improved the PCEs and large grain size (micrometer scale) of the perovskite layer because of defect passivation and interface modification; the amide group exhibited a Lewis base adduct property coordinated to Ni and Pb ions in NiO x and perovskite, bifacial defect passivation and reduced the grain boundaries to improve the crystallinity of the perovskite. The amide-based SY2 exhibited the stronger interaction with the perovskite layer than that of ester-based SY1, which is related to the observations in X-ray absorption near edge structure (XANES). The best performance of the NiO x /SY2 device was characterized by a short-circuit current density (J sc) of 21.76 mA cm–2, an open-circuit voltage (V oc) of 1.102 V, and a fill factor of 79.1%, corresponding to an overall PCE of 18.96%. The stability test of the PCE of the NiO x /SY2 PSC device PCE showed a decay of only 5.01% after 168 h; it retained 92.01% of its original PCE after 1000 h in Ar atmosphere. Time-resolved photoluminescence spectra of the perovskite films suggested that the hole extraction capabilities of the NiO x /SY-HTMs were better than that of the bare NiO x . The superior film morphologies of the NiO x /SY-HTMs were responsible for the performances of their devices being comparable with those of bare NiO x -based PSCs. The photophysical properties of the HTMs were analyzed through time-dependent density functional theory with the B3LYP functional.