Propylammonium Chloride Additive for Efficient and Stable FAPbI₃ Perovskite Solar Cells

Abstract

However, the unsatisfied moisture stability of the perovskite materials may become an obstacle for practical applications of PSCs. [5,6] Formamidinium lead iodide (FAPbI 3 ) is a widely used composition for high efficiency PSC owing to its superior properties such as optimal bandgap, high absorption coefficient and long carrier diffusion length, which is better than a prototype perovskite composition of methylammonium lead iodide (MAPbI 3 ). [7][8][9][10][11][12][13] FAPbI 3 has two phases, a nonperovskite heaxagonal phase (δ phase) and cubic perovskite phase (α-phase). [9] Normally, the phase transformation from δ-phase to α-phase FAPbI 3 requires the annealing temperature higher than 120 °C. [14] However, fabricating pure α-FAPbI 3 is a challenging due to the metastable α-FAPbI 3 , where the residual δ-phase forces α-phase to undergo a reverse phase transition back to δ-phase in the room temperature. [15][16][17][18] It has been known that α-phase FAPbI 3 can be stabilized by a partial substitution of FA and/or I with Cs, MA and Rb cation, and Br anion. Nevertheless, stabilizing the pure α-phase FAPbI 3 is crucial for achieving higher efficiency. [15,16,[19][20][21][22][23] Instead of substitution strategy, MACl has been proposed as an additive in perovskite precursor solution for inducing pure α-FAPbI 3 perovskite. It was found that addition of MACl increased crystallinity and grain size as well as formation of the pure black phase perovskite film. [12,24,25] However, an increase of bandgap cannot be excluded due to a potential incorporation of To achieve high efficiency perovskite solar cells (PSCs) based on α-phase formamidinium lead iodide (FAPbI 3 ), addition of methylammonium chloride (MACl) in the precursor solution is commonly used, mainly because of phase stability and improvement of grain size and crystallinity. However, the instability of MA in the perovskite limits the device long-term stability. In this report, n-propylammonium chloride (PACl) is proposed as an alternative to MACl for more stable and efficient FAPbI 3 -based PSCs. Perovskite grain size is increased after addition of PACl. Unlike the MA cation, the propylammonium cation passivates the grain boundary rather than being incorporated into the perovskite lattice due to larger ionic size, which minimizes the change in bandgap. Carrier lifetime is significantly increased by more than five times from 405 to 2110 ns with the PACl additive with negligible trap-mediated recombination, while only four times longer carrier lifetime is observed by MACl additive. As a result, a power conversion efficiency over 22.2% is achieved by 20 mol% PACl additive, which is one of the best efficiencies among the MA-free and Br-free PSCs. In addition, stability against moisture is much better for PACl than for MACl due to an in situ formed barrier at the bulk perovskite.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aenm.202102538.

Indigo: A Natural Molecular Passivator for Efficient Perovskite Solar Cells

“…The Indigo treated perovskite film exhibits a longer average lifetime (τ ave ) (455 ns for the 0.05 mg mL −1 ) than the control one (300 ns), suggesting a higher-quality film with suppressed trap-assisted nonradiative recombination. [50,51] In comparison with the conventional PL spectroscopy, 2D PL mapping imaging allows us to assess the uniformity of the perovskite film (Figure 4c,d). More uniform intensity distribution was found in the Indigo treated perovskite film relative to the pristine one, which may result from the elimination of defects at both the surface and grain boundaries.…”

Post‐Treatment Passivation by Quaternary Ammonium Chloride Zwitterion for Efficient and Stable Perovskite Solar Cells

“…The peaks at 138.35 and 143.2 eV for pristine perovskite are attributed to the two states of Pb 2+ species, respectively, Pb 4 f 7/2 and Pb 4 f 5/2 . [ 48 ] Compared to the peaks of pristine perovskite, those peaks of TC‐treated perovskite shifts to lower binder energy of 138.05 eV and 142.9 eV with value of 0.3 eV. This indicates that TC molecule has interaction with Pb in perovskite.…”

Phase‐Pure Engineering for Efficient and Stable Formamidinium‐Based Perovskite Solar Cells

“…For example, Zhang et al attempted to use n-propylammonium chloride (PACl) instead of MACl to achieve more stable and efficient FAPbI 3 -based PSCs. [193] The transformation between the black phase and yellow phase of FAPbI 3 is mainly from the change of lattice stress. Different interface layers or transport layers can be designed to control the lattice stress, such as dynamic resonance organic molecules.…”

“…For example, Zhang et al attempted to use n ‐propylammonium chloride (PACl) instead of MACl to achieve more stable and efficient FAPbI 3 ‐based PSCs. [ 193 ]…”