Interface Passivation of Inverted Perovskite Solar Cells by Dye Molecules

The interface between [6,6]-phenyl C₆₁-butyric acid methyl ester (PC₆₁BM) and the electrode has a critical effect on the performance of inverted perovskite solar cells (PSCs). Three organic cationic cyanine dye molecules with different highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states are designed to passivate the PC₆₁BM and Ag electrode interface to improve PSCs performance. The effects of energy-level alignment and the interfacial charge transfer resistance on the device performance are compared and studied. The dye interface passivation layer significantly reduces charge recombination. Moreover, the ClO₄^– anions associated with the dye molecules improve the charge extraction and charge transport in the devices. Reduced interface charge recombination and improved charge transport are confirmed by photoluminescence (PL), time-resolved photoluminescence (TRPL), electrochemical impedance spectra (EIS), and charge-only device performance studies. The PSCs with one of the dyes as an interface passivation layer show an optimized power conversion efficiency (PCE) of 19.14% with an open-circuit voltage (V_oc) of 1.09 V, a short-circuit current density (J_sc) of 22.87 mA/cm², and a fill factor (FF) of 76.81%. The devices maintain over 90% of the initial PCE for 120 h of storage under an ambient environment (25 °C and 30 ± 5% relative humidity (RH). The use of small dye molecules as an interface passivation layer to reduce charge recombination in PSCs represents a paradigm for improving the performance and stability of PSCs.