Volatile 2D Ruddlesden‐Popper Perovskite: A Gift for α‐Formamidinium Lead Triiodide Solar Cells

Abstract

Perovskite solar cells with increasingly pure composition of α-formamidinium lead triiodide (α-FAPbI 3 ) perovskite are utilized to set more and more record-breaking efficiencies. However, pure α-FAPbI 3 perovskite is unstable and difficult to prepare. Here, a series of bulky alkylammoniums known as the spacer cations (RP cations) of 2D Ruddlesden-Popper perovskites (2D perovskites) are used to prepare α-FAPbI 3 perovskite films. The deprotonation process of RP cations during annealing removes the in situ generated 2D perovskites from the film, which determines the phase and compositional purity, crystallinity, and stability of α-FAPbI 3 perovskite films and depends on the design of RP cations. Only a small number of residual RP cations (0.3-2.3%) are found anchoring at grain boundaries. As a result, α-FAPbI 3 perovskite solar cells prepared from RP cations, especially 2-thiophenemethylammonium, show higher efficiency and stability than control devices prepared from the most commonly used methylammonium. It is believed that in situ generated 2D perovskites are ideal additives for α-FAPbI 3 perovskite, because a large addition (20%) of 2D perovskites ensures the preparation of high-quality phase-pure α-FAPbI 3 perovskite films, while a small number of residual RP cations anchored at grain boundaries guarantee the performance and stability of α-FAPbI 3 perovskite solar cells.

Volatile 2-Thiophenemethylammonium and Its Strongly Bonded Condensation Product for Stabilizing α-FAPbI3 in Sequential-Deposited Solar Cells

“…Only trace amount of TMA (0.005%–0.12%) remains in the perovskite film (Table S1 in the Supporting Information). Interestingly, the signal belonging to the thermally stable and nonvolatile condensation product (TMFA) between TMA and FA appears in the perovskite film, which has been studied in detail in our previous work, and its intensity is stronger than that of TMA, as shown in Figure S5 in the Supporting Information. Specifically, the amount of residual TMA and TMFA in the perovskite film of TMA3 is 0.02% and 0.10%, respectively.…”

“…13−16 We also noticed that part of the spacer cations will react with formamidinium (FA) in the perovskite film to form the nonvolatile and thermally stable condensation product. 17 We are looking for a strategy to simultaneously exploit the properties of the spacer cations of 2D perovskites to prepare high-quality perovskite films and stabilize them by the condensation product.…”

“…The spacer cations of 2D perovskites, such as phenylethylammonium (PEA) and butylammonium (BA), are widely used to construct 3D/2D heterojunctions or stabilize perovskite films by doping into the film. , More recently, Seok et al . and our group independently find that the spacer cations of 2D perovskites are volatile during annealing and the presence of the spacer cations in the perovskite precursor solution can promote the formation and stabilization of α-formamidinium lead triiodide (α-FAPbI 3 ) films. − We also noticed that part of the spacer cations will react with formamidinium (FA) in the perovskite film to form the nonvolatile and thermally stable condensation product . We are looking for a strategy to simultaneously exploit the properties of the spacer cations of 2D perovskites to prepare high-quality perovskite films and stabilize them by the condensation product.…”

Synergy of 3D and 2D Perovskites for Durable, Efficient Solar Cells and Beyond

“…Additionally, the sulfur ion in TMA binds with the Pb to passivate the iodine vacancy sites, reducing defect assisted recombination. n-i-p devices made with TMA cations demonstrated a PCE of 22.1% with 2.3% hysteresis index and retained 93% of their PCE in 1440 h during shelf storage in 25% RH …”

DMSO‐Free Solvent Strategy for Stable and Efficient Methylammonium‐Free Sn–Pb Alloyed Perovskite Solar Cells

“…The films fabricated through D-A or D/N solvents contains nonperovskite phase (δ-phase) at diffraction peaks of 10.1°and 13.2°, which is useless and more detrimental for phase stability. [37,38] After applying D/P treatment, the δ-phase is greatly eliminated in film surface. Moreover, the intensities of (110), (202), and (220) for D/P treated perovskite crystal planes are almost two times higher than that of the D/S film.…”