Anchoring self-assembled monolayer at perovskite/hole collector interface for wide bandgap Sn-based solar cells with a record efficiency over 12%

In perovskite solar cells (PSCs), surface and interfacial conditions play a crucial role in determining overall device performance. In typical p-i-n architecture of wide bandgap (WBG, 1.6–1.8 eV) Sn-based PSCs, the interface between hole transport layer (HTL) and perovskite (PVK) has a significant impact on hole transport, interfacial chemical interactions, and perovskite film quality. This study aims to address these issues by incorporating self-assembled monolayers (SAMs) MeO-2PACz and 2PACz at the PEDOT:PSS HTL/Sn-PVK interface. X-ray photoelectron spectroscopy confirmed the interaction between the anchoring group (P-O−) of the SAM and S+ in PEDOT:PSS through phosphonic acid deprotonation at the interface, and improved work function was observed through the UPS study. Furthermore, the SAMs contributed to the formation of a compact PVK film with enhanced preferential orientation. Interestingly, a chemical interaction between the oxygen-donor of the methoxy (CH3O−) terminal group in MeO-2PACz and the Sn-halide octahedra was observed, which partly contributed to suppress the oxidation of Sn2+ state and defect density of perovskite. Additionally, femtosecond transient absorption spectroscopy (fs-TAS) showed faster trap filling (τ1) characteristics (τ1∼19 ps). Fs-TAS and photoluminescence further indicated fast hole extraction (τ2∼125 ps) as well as high quenching efficiency of 47%. Based on these findings, an unprecedented efficiency of η∼12.16% (certified 11.60%) was achieved in WBG Sn-PSCs using the HTL/MeO-2PACz/PVK structure, outperforming the HTL/2PACz/PVK (8.78%) and HTL/PVK (7.44%) structures. This study provides crucial guidelines on interfacial engineering for WBG Sn-PSCs.