Deciphering the Roles of MA-Based Volatile Additives for α-FAPbI₃ to Enable Efficient Inverted Perovskite Solar Cells

Abstract

Functional additives that can interact with the perovskite precursors to form the intermediate phase have been proven essential in obtaining uniform and stable α-FAPbI 3 films. Among them, Cl-based volatile additives are the most prevalent in the literature. However, their exact role is still unclear, especially in inverted perovskite solar cells (PSCs). In this work, we have systematically studied the functions of Cl-based volatile additives and MA-based additives in formamidinium lead iodide (FAPbI 3 )based inverted PSCs. Using in situ photoluminescence, we provide clear evidence to unravel the different roles of volatile additives (NH 4 Cl, FACl, and MACl) and MA-based additives (MACl, MABr, and MAI) in the nucleation, crystallization, and phase transition of FAPbI 3 . Three different kinds of crystallization routes are proposed based on the above additives. The non-MA volatile additives (NH 4 Cl and FACl) were found to promote crystallization and lower the phase-transition temperatures. The MA-based additives could quickly induce MA-rich nuclei to form pure α-phase FAPbI 3 and dramatically reduce phase-transition temperatures. Furthermore, volatile MACl provides a unique effect on promoting the growth of secondary crystallization during annealing. The optimized solar cells with MACl can achieve an efficiency of 23.1%, which is the highest in inverted FAPbI 3 -based PSCs.

Target Therapy for Buried Interface Enables Stable Perovskite Solar Cells with 25.05% Efficiency

“…Most of the works with certified PCE exceeding 25% have focused on the fine control of the perovskite crystallization process and surface defect passivation. [5,[25][26][27] This suggests that minimizing the non-radiative recombination loss in the bulk perovskite and at the charge-transporting layer (CTL)/perovskite interface is crucial for further closing the efficiency gap to reach the Shockley-Queisser (SQ) limit. [28,29] Colloidal SnO 2 has become the most used ETL in n-i-p PSCs (Figure 1b).…”

Low-temperature synergistic effect of MA and Cl towards high-quality α-FAPbI3 films for humid-air-processed perovskite solar cells

“…Previous studies have demonstrated that MA can reduce the formation energy of the α-FAPbI 3 structure and Cl can enhance the interaction of FA and I, which is conducive to the stability of α-FAPbI 3 . 31,49 However, the kinetic and thermodynamic mechanisms of MA or Cl behavior are still unclear. In order to further clarify the respective roles of MA and Cl in the crystallization of α-FAPbI 3 films, IPA, MAI/IPA and FACl/IPA in the same molar ratio were chosen to replace MACl/IPA to fabricate perovskite films by the same CSA method at 100 °C.…”

Deciphering Reaction Products in Formamidine-Based Perovskites with Methylammonium Chloride Additive

“…Compared with 3C-FAPbI 3 of 1.409 eV, the band gap increases by about 0.013 eV, indicating that chloride ions mainly increase the band gap of 3C-FAPbI 3 single crystal caused by MACl additives. 24,36,49,50 Figure 7d presents the average results of multiple measurements: about 2% chlorine contributes to an increase of about 0.01 eV in the band gap. In comparison, 1% MFAI is associated with an increase of about 0.003 eV, whereas about 7% MA cations has almost no influence on the band gap.…”