The Formation Mechanism of (001) Facet Dominated α‐FAPbI₃ Film by Pseudohalide Ions for High‐Performance Perovskite Solar Cells

Abstract

Formamidinium lead triiodide (𝜶-FAPbI 3 ) has been widely used in high-efficiency perovskite solar cells due to its small band gap and excellent charge-transport properties. Recently, some additives show facet selectivity to generate a (001) facet-dominant film during crystallization. However, the mechanism to realize such (001) facet selectivity is not fully understood. Here, the authors attempted to use three ammonia salts NH 4 X (X are pseudohalide anions) to achieve better (001) facet selectivity in perovskite crystallization and improved crystallinity. After addition, the (001) facet dominance is generally increased with the best effect from SCN − anions. The theoretical calculation revealed three mechanisms of such improvements. First, pseudohalide anions have larger binding energy than the iodine ion to bind the facets including ( 110), (210), and (111), slowing down the growth of these facets. The large binding energy also reduces nucleation density and improves crystallinity. Second, pseudohalide ions improve phase purity by increasing the formation energies of the 𝜹-phase and other hexagonal polytypes, retarding the 𝜶to 𝜹-phase transition. Third, the strong binding of these anions can also effectively passivate the iodine vacancies and suppress nonradiative recombination. As a result, the devices show a power conversion efficiency of 24.11% with a V oc of 1.181 V.

Enhancing Spectral Response of Thermally Stable Printed Dion–Jacobson 2D FAPbI3 Photovoltaics via Manipulating Charge Transfer

“…The XRD showed in Figure 2a evidence that the two-layered perovskite films exhibit rather similar diffraction characteristics, where the two intense peaks at ∼14.09°and ∼28.24°are indexed to the (111) and (202) diffraction planes of layered α-FAPbI 3 crystals. 47,48 These observations suggest that the addition of a small amount of TU (2.5%) does not impact the crystal structure and crystallinity of the perovskite films. However, further increasing the content of TU to over 5%, the intensity of main diffraction peak becomes stronger, along with the formation of δ-phase (Figure S7a).…”

Temperature and pressure induced structural transitions of lead iodide perovskites

“…The α-FAPbI 3 film usually contains a δ-phase impurity, which reduces light absorption and retards device efficiency. 113 It is worthwhile to note that α-FAPbI 3 is more attractive than α-MAPbI 3 and α-CsPbI 3 because its bandgap is closer to the theoretically optimal bandgap (1.4 eV) required for solar cells.…”

Performance enhancement of inverted perovskite solar cells using a GlyHCl additive

“…10 Therefore, it is a feasible strategy to improve the performance of PSCs by controlling the growth orientation of perovskite films towards (001). 11–13…”