P-Dopant with Spherical Anion for Stable n-i-p Perovskite Solar Cells.

Li-TFSI/t-BP is the most widely utilized p-dopant for hole-transporting materials (HTMs) in state-of-the-art perovskite solar cells (PSCs). However, its nonuniformity of doping, along with the hygroscopicity and migration of dopants, results in the devices that exhibit limited stability and performance. This study reports the use of a spherical anion of the p-dopant, regulated by its radius and shape, as an alternative to the linear TFSI- anion. The theoretical and experimental results reveal that the spherical anion significantly increases the doping of HTMs due to an enhanced electron transfer from larger dipoles. The enhanced transfer leads to a shift in the Pb-6p defect orbitals, resulting in the shallower trap states.  The linear structure of the TFSI- anion, the p-dopant anion with a larger van der Waals radius and spherical shape offers increased hydrophobicity and migration barriers protecting the perovskite. The use of sodium tetrakis(3,5-bis(trifluoro methyl)phenyl)borate results in enhanced thermal and ambient stability of PSCs. The devices fabricated with the shape- and radius-regulated p-dopant achieve remarkable efficiencies of 24.49% and 24.31% for CJ-01 and spiro-OMeTAD, respectively, representing the highest efficiency values for organic dopants to date. This study underscores the ingenious design of spherical anions as p-dopants.