Spiro[cyclopentadithiophene-dioxolane]-Based D-A-D Type Organic Molecule for Both Crystallization Improvement and Band Adjustment of Perovskites.

Abstract

To improve the crystallization and meanwhile adjust the band levels of perovskites, we design and synthesize a novel organic molecule, 4,4'-(spiro[cyclopenta[1,2-b:5,4-b']dithiophene-4,2'-[1,3]dioxolane]-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (TM1), to dissolve in an antisolvent for the antisolvent engineering of perovskite solar cells (PSCs). The coordination interactions between TM1 and Pb2+ ions in perovskites and the hydrogen bonds between the O atoms in the methoxy of TM1 and the MA+ in perovskites are characterized with X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Owing to these interactions, TM1 can improve the perovskite crystallization, which reduces the trap density, enhances the interfacial hole extraction, and retards charge recombination as well, boosting short-circuit photocurrent notably. TM1 also shifts the valence band of perovskites upward by 0.17 eV, which aligns better with the highest occupied molecular orbital of hole transport materials and thus increases the open-circuit photovoltage significantly. As a result, the power conversion efficiency is enhanced from 17.22 to 20.21% by TM1. Moreover, TM1 can also improve device stability significantly. These findings demonstrate that TM1 is a kind of functional material as an additive in an antisolvent for both crystallization improvement and energy level adjustment of perovskites toward highly efficient and stable PSCs.