Bifunctionally engineering a PEDOT:PSS/perovskite buried interface for tin perovskite solar cells via...

Tin (Sn) perovskite solar cells (Sn-PSCs) employing poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as the hole transport layer represent one of the most promising architectures. However, their performance is severely limited by the insulating and hygroscopic nature of the PSS component, along with unfavorable energy-level alignment and a high defect density at the buried interface. In this work, we report an effective interfacial modification strategy by introducing 4-cyanophenylhydrazine hydrochloride (4CHP) onto the surface of PEDOT:PSS. The strong electron-withdrawing cyano group in 4CHP increases the quinoid contribution of PEDOT, promoting π-electron delocalization and charge transport along the polymer backbone, which in turn facilitates charge transport across the buried interface. In addition, the electrostatic interaction between 4CHP and PSS modifies the local chemical environment of PSS and reduces its relative exposure at the buried interface. This interfacial regulation reduces the direct influence of the insulating and acidic features of PEDOT:PSS, thereby improving interfacial charge transport and mitigating unfavorable chemical interactions with the Sn perovskite. Moreover, the hydrazine group in 4CHP acts as an efficient reducing agent that suppresses the oxidation of Sn²⁺ and mitigates p-type self-doping in the perovskite layer, resulting in an improved buried interface quality. Consequently, the optimized devices deliver an increased power conversion efficiency from 12.26% to 14.25% and retain about 90% of their initial efficiency after 112 hours of continuous operation. This work provides insights into molecular-level regulation of the buried interface and underscores the importance of multifunctional interfacial modifiers for stabilizing Sn-PSCs.