Enhanced efficiency and stability of Dion–Jacobson quasi-two-dimensional perovskite solar cells by additive

Dion–Jacobson (DJ) quasi-two-dimensional (quasi-2D) perovskite solar cells (PSCs) have attracted increasing attention owing to their potential stability compared with the Ruddlesden-Popper (RP) phase. It is known that the low efficiency and poor thermal stability retard the application of quasi-2D PSCs. Here, DJ quasi-2D perovskite films based on propane-1.3-diammonium (PDA) spacer cations were prepared by a hot casting technique. Ionic liquid additive of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) was introduced into the quasi-2D perovskite precursor solution to improve the crystal quality and morphology of the films. The quasi-2D PSCs with BMIMBF4 achieved an optimal power conversion efficiency (PCE) of 14.07%, which is higher than the 12.45% of the control devices. The impressive 1.17 V high open-circuit voltage and 14.07% efficiency are the highest values for the reported PDA-based n–i–p type devices. Moreover, the thermal stability of the solar cells was significantly enhanced by the addition of BMIMBF4. The PCE of the devices with BMIMBF4 maintains 72% of the initial value after annealing at 85 °C for 120 h, while the PCE of control devices drops to 19% of the initial value. These results prove that the introduction of ionic liquid BMIMBF4 is a pragmatic method to elevate the efficiency and thermal stability of quasi-2D PSCs.