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

Abstract

The perovskite films prepared by the sequential deposition method suffer from incomplete lead iodide (PbI2) reaction, which is manifested by the poor photostability of the prepared perovskite solar cells. Herein, 2-thiophenemethylammonium (TMA), known for the formation of Ruddlesden–Popper layered perovskites, is used to modify the PbI2 film. The introduction of TMA reduces the crystallinity of PbI2 and participates in the formation of the solvent intermediate phase, thus promoting the formation of α-formamidinium lead triiodide (α-FAPbI3) perovskite films in the whole film thickness direction. Most of TMA escapes from the film by deprotonation, and only trace amounts of TMA (0.02%) and the condensation product (TMFA, 0.10%) between TMA and formamidinium (FA) are found to be strongly bonded to the perovskite grain boundaries. The results show that the stability of the perovskite solar cell is improved and the power conversion efficiency reaches 24.5%. This discovery confirms the great value of volatile alkylammoniums in the preparation and stabilization of α-FAPbI3 perovskite films.

Two-dimensional perovskite templates for durable, efficient formamidinium perovskite solar cells

“…Other reports have suggested that the A′ cation of 2D perovskites incorporated into FAPbI 3 volatilized completely during annealing except for a small fraction left at grain boundaries ( 19 , 38 , 39 ), which would also explain the disappearance of our 2D signal over time and the slow increase in the (001) 3D peak intensity during annealing at 150°C. Solid-state 1 H NMR on scraped films of FAPbI 3 with added 2D before and after annealing did reveal a partial volatilization of the spacer cation during film formation but also confirmed appreciable fractions of BA and PA even after annealing at 150°C for 20 min (figs.…”

Narrow Bandgap Metal Halide Perovskites for All-Perovskite Tandem Photovoltaics

“…These interesting in situ chemical reactions occurring between the neutral amines or other molecules, such as bis-diazirine, and the organic cation(s) of the precursor material offer huge potential for further exploration/improvement in PSCs and other perovskite-based applications. In particular, precisely targeted chemical reactions or surface species can be implemented into the perovskite system for specific aims. ,− Various unexpected/underexplored chemical reactions generated in this complex system also make the perovskite research more exciting.…”

“…Methylenediammonium (MDA 2+ ) also oligomerizes into hexamethylenetetramine (HMTA), which can then react with FA + to form tetrahydrotriazinium (THTZ-H + ) . These reactions can potentially happen at the solid film surface, for example, when it is modified with 3-(aminomethyl)­pyridine (3-APy) and likely 2-thiophenemethylamine (TMA), EDA, and other alkylamines. , In the case of 3-APy, the product is N -(3-methylpyridine) formamidinium (MPyFA + ), or for amine-MA + reaction, a simple transfer or sharing of acidic protons happens, forming 3-APy + . The authors further claimed that the formed MPyFA + cation sits at the A-site of the perovskite, with the pyridine ring promoting the formation of positively charged V I (iodide vacancies), which act as shallow donors and induce a field that facilitates electron extraction.…”