Hybrid organic-inorganic perovskite solar cells (PSCs) have dramatically increased the power conversion efficiency (PCE) from 3.8% to 25.2% in a decade. The scientists realized such a stunning improvement by simply tuning the composition of the perovskite absorber materials. These materials are based on the ABX3 structure, where A is a monovalent cation, e.g., organic methylammonium (MA), formamidinium (FA), or inorganic Cs+, B is a divalent metal (such as Pb2+ or Sn2+), and X is a halide ion (Cl–, Br–, or I–). The bandgap of a perovskite can be tunable by replacing large halides (e.g., I–) with smaller halides (e.g., Br–), resulting in an increase in the bandgap, whereas swapping Pb2+ with Sn2+ results in a decrease in the bandgap. Another method for customizing optoelectronic properties is to produce low-dimensional perovskites by introducing bigger organic cations. We show how to alter the α-FAPbI3 phase with benzylammonium (Bz) cations to stabilize it. According to density functional theory studies, benzylamine has a delocalized π-system that extends throughout the whole molecule, which may help decrease the barrier for charge-carrier transport compared to other phenyl analogues. We show that BzI may interact with -FAPbI3 at the atomic level via hydrogen bonding, as demonstrated by solid-state NMR spectroscopy, stabilizing it against the detrimental α-to-δ phase transition. The addition of benzylammonium (Bz) iodide resulted in the stability of the black perovskite α-FAPbI3 phase. We show that Bz interacts with α-FAPbI3 to make it more stable. The Bz moieties modify the surface of the FAPbI3 and the grain boundaries in this phase without producing low-dimensional perovskite phases. This modulation strategy strongly enhances the optoelectronic quality of the perovskite phase, as shown by PLQY and TRPL measurements. Consequently, perovskite solar cells based on FAPbI3(BzI)0.25 exhibit more than 20% power conversion efficiencies and excellent stability, retaining 80% of the initial PCE after one year under ambient shelf-life conditions. As a result, this technique offers a novel method for maintaining the black (α) perovskite phase of FAPbI3 in perovskite solar cells.

Benzylammonium-mediated formamidinium lead iodide perovskite phase stabilization for photovoltaics

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.