Donor-Acceptor Zwitterion as Self-Assembled Hole-Selective Layer for Highly Efficient Tin-Based Perovskite Solar Cells

Abstract

The development of tin-based perovskite solar cells (TPSCs) has lagged far behind that of their lead-based counterparts. Although there have been many reports on efficient TPSC, most of them are based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole-selective layer (HSL), whose strong acidity and hygroscopicity are undoubtedly highly detrimental to the long-term stability of the devices. Here, a donor-acceprtor-type zwitterionic molecule (namely PyPs) was designed by employing a triphenylamine donor and a benzo[c][1,2,5]thiadiazole acceptor as the molecular backbone, functionalized with pyridinium sulfonate terminal group, respectively. The ionic sulfonate group in PyPs enable uniform surface coverage and improved energy-level alignment, while also favoring the growth and defect passivation of tin perovskite. As a result, high-quality Sn-based perovskite films can be obtained along with the accelerated interfacial charge extraction and suppressed non-radiative recombination losses. Encouragingly, PyPs-based devices deliver a champion power conversion efficiency (PCE) of 12.18%, representing the highest efficiency reported to date for TPSCs based on self-assembled HSLs. Moreover, unencapsulated PyPs-based devices retain 90% of their initial PCE after 1800 h of storage. This work highlights the potential of rational molecular design toward the exploration of alternative HSLs for efficient and stable TPSCs.