Key points are not available for this paper at this time.
Fullerene derivatives have been popularly applied as electron transport layers (ETLs) of inverted (p–i–n) planar heterojunction perovskite solar cells (iPSCs) due to their strong electron-accepting abilities, and so far, 6,6-phenyl-C 61 -butyric acid methyl ester (PCBM) has been the most commonly used ETL, which suffers, however, from high cost due to the complicated synthetic route. Herein, novel pyridine-functionalized fullerene derivatives (abbreviated as C 60 -Py) were synthesized facilely via a one-step 1,3-dipolar cycloaddition reaction and applied as ETLs superior to PCBM in iPSC devices. Three pyridine-functionalized fullerene derivatives with different alkyl groups, including methyl, n -butyl, and n -hexyl, grafted onto the pyrrolidine moiety (abbreviated as C 60 -MPy, C 60 -BPy, and C 60 -HPy, respectively) were synthesized. According to cyclic voltammogram study, the chain length of the N -alkyl group has negligible influence on the molecular energy level of C 60 -Py. However, the ETL performance of C 60 -Py is sensitively dependent on the chain length of the N -alkyl group, with C 60 -BPy exhibiting the highest power conversion efficiency (PCE) of 16.83%, which surpasses that based on PCBM ETL (15.87%). The PCE enhancement of C 60 -BPy device is attributed to the coordination interactions between the pyridine moiety with the Pb 2+ ion of CH 3 NH 3 PbI 3 perovskite, which anchor C 60 -BPy onto perovskite film and reinforce the passivation of the trap state within the CH 3 NH 3 PbI 3 perovskite film and suppress the nonradiative electron–hole recombinations, leading to enhanced electron transport reflected by the increase of short-circuit current density ( J sc ). The ambient stability of C 60 -HPy-based device is much better than that based on PCBM ETL since its long N -alkyl group can function as a superior encapsulating layer protecting the CH 3 NH 3 PbI 3 layer from contact with the ambient moisture.
Li et al. (2018) studied this question.