Efficient and Stable Perovskite Solar Cells via Multi-Functional Guanylurea Phosphate Zwitterionic Bridging Strategy.

[Display omitted] • A novel zwitterionic bridging strategy is proposed to passivate bifacial defects. • The planar conjugated structure of GUP enhances the structural stability of perovskite and releases residual stresses. • The optimized PSCs exhibited an increase in PCE from 21.23% to 24.03%, with an open-circuit voltage of up to 1.172 V • The multifunctional flame retardant facilitates bridging between ETL and perovskite, enhancing the stability of PSCs. Buried interface defects and residual stresses significantly impede further improvements in the efficiency and stability of perovskite solar cells (PSCs). Herein, a flame retardant guanylurea phosphate (GUP) with multisite anchors serves as the zwitterionic bridge between SnO 2 and perovskite. The phosphate groups within GUP facilitate bridging between SnO 2 and perovskite while concomitantly passivating bifacial defects, thereby significantly inhibiting non-radiative recombination at the buried interface. Simultaneously, the planar configuration of the amidinourea unit strengthens the binding of amino (–NH 2) and carbonyl (C=O) groups with [PbI 6 ]4−, which enhances perovskite structure stability and relieves residual stresses. Contributing to the zwitterionic bridging strategy of multi-functional flame retardant, the power conversion efficiency (PCE) of GUP-treated PSCs significantly increased from 21.23 % to 24.03 %, with an open-circuit voltage (V OC) of up to 1.172 V, and exhibited outstanding stability. Unencapsulated PSCs treated with GUP maintained about 93.86 % and 80.53 % of their original efficiency after 1200 h of aging in the air at 25 °C with 25 ± 5 % relative humidity (RH) and after 600 h of aging in the air at 85 °C and 10 ± 5 % RH, respectively. [ABSTRACT FROM AUTHOR]