Fluorinated Aromatic Formamidinium Spacers Boost Efficiency of Layered Ruddlesden–Popper Perovskite Solar Cells

Abstract

Layered two-dimensional (2D) perovskites are emerging photovoltaic materials due to their good environmental and structural stability thanks to the bulky organic spacers incorporated in the crystal lattice. Formamidine (FA) is an indispensable organic cation in high-performance 3D perovskite materials, whereas FA derivative-based spacers have remained largely unexplored in 2D perovskite. Here, we demonstrated a class of aromatic formamidinium (ArFA) spacers, namely, benzamidine (PhFA) and para-fluorobenzamidine (p-FPhFA), for efficient 2D Ruddlesden–Popper (RP) perovskite solar cells. It is found that the 2D perovskite with the fluorinated spacer p-FPhFA shows significantly improved charge carrier lifetime, enhanced mobility, and reduced trap density in comparison with an unfluorinated PhFA spacer. As a result, the p-FPhFA-based 2D perovskite (n = 5) device yields a champion efficiency of 17.37%, which is much higher than that of the PhFA-Pb device (12.92%), representing a record value for 2D PSCs with FA-based spacers. These results highlight the great potential of ArFA spacers, especially the fluorinated ArFA spacer, for high-performance 2D perovskite solar cells.

A Novel Multiple‐Ring Aromatic Spacer Based 2D Ruddlesden–Popper CsPbI3Solar Cell with Record Efficiency Beyond 16%

“…Thereby, the Coulomb force between the electron and hole pairs of the excitons is reduced, promoting efficient charge separation. [30,31] Figure 1b illustrates several possible carrier transport channels between the interlayers. H bond: the −NH 3 + functional groups of PEA + and 1-NA + cations occupy the site of Cs + and connect the inorganic layer through NH⋯I hydrogen bonds.…”

“…Thereby, the Coulomb force between the electron and hole pairs of the excitons is reduced, promoting efficient charge separation. [ 30,31 ]…”

Emerging doping strategies in two-dimensional hybrid perovskite semiconductors for cutting edge optoelectronics applications

“… 105 Liu et al developed FA derivative-based spacers for 2D RP perovskites and studied the effect of fluorine in organic spacers. 106 They have synthesized perovskite films of benzamidine (PhFA) [(PhFA) 2 MA n −1 Pb n I 3 n +1− x Cl x ( n = 5)] and para -fluorobenzamidine ( p -FPhFA) [( p -FPhFA) 2 MA n −1 Pb n I 3 n +1− x Cl x ( n = 5)] using a one-step spin-coating method. 106 The perovskite solution was prepared by mixing all the precursors ( p -FPhFA or PhFA, MAI, and PbI 2 ) in a particular stoichiometric ratio in DMF.…”

“… 106 They have synthesized perovskite films of benzamidine (PhFA) [(PhFA) 2 MA n −1 Pb n I 3 n +1− x Cl x ( n = 5)] and para -fluorobenzamidine ( p -FPhFA) [( p -FPhFA) 2 MA n −1 Pb n I 3 n +1− x Cl x ( n = 5)] using a one-step spin-coating method. 106 The perovskite solution was prepared by mixing all the precursors ( p -FPhFA or PhFA, MAI, and PbI 2 ) in a particular stoichiometric ratio in DMF. The diffraction peak intensity ratio of (202)/(111) increases from 0.32 to 0.48 for the p -FPhFA film compared to the PhFA film, indicating more inclination towards vertical growth on the substrate, thus facilitating efficient charge transport in the device.…”

“…The diffraction peak intensity ratio of (202)/(111) increases from 0.32 to 0.48 for the p -FPhFA film compared to the PhFA film, indicating more inclination towards vertical growth on the substrate, thus facilitating efficient charge transport in the device. 106 However, parallel and vertical growth slabs coexist in the PhFA layered perovskite crystal film, which could block efficient charge transport. 106 Hence, molecular doping in layered perovskites is still underexplored, and it should be investigated further to unveil the detailed mechanism and its effect on electronic properties.…”