Fluoroethylamine Engineering for Effective Passivation to Attain 23.4% Efficiency Perovskite Solar Cells with Superior Stability

Abstract

Defects in perovskite layers usually cause nonradiative recombination, impairing device performance and stability. Here, fluoroethylamine (FC2H4NH3, FEA) is integrated into the perovskite film to passivate defects. By engineering of different amounts of fluorine in the molecule, it is found that when 2‐fluoroethylamine (1FEA), in which one F bonds to the first carbon atom at the end of the molecule's structure, is used, the F atoms appear to be distributed throughout the bulk to the very surface. When 2,2‐difluoroethylamine (2FEA) and 2, 2, 2‐trifluoroethylamine (3FEA) are used, F is prone to distribution in the bulk of the perovskite film, while there appears to be no detectable F content on the surface. With the FEA passivation, the nonradiative recombination is suppressed, the carrier‐lifetime is improved to 840.01 ns, and the film‐air interface offers greater hydrophobicity, especially in the case of 1FEA, where because it is distributed throughout the film thickness, it passivates more defects and delivers the highest efficiency, as much as 23.40%. The device with 3FEA shows the best environmental stability; specifically, the bare cell without any encapsulation maintains 87% of its initial efficiency after exposure to the ambient environment for 1200 h.

Stable 24.29%‐Efficiency FA0.85MA0.15PbI3 Perovskite Solar Cells Enabled by Methyl Haloacetate‐Lead Dimer Complex

“…[22,23] However, the low-boilingpoint MA cations easily escape from the perovskite lattice during the device fabrication process, and the large FA cations are impeded from embedding into the MA vacancies due to their weak interaction with the established lattice, both of which lead to many defects (MA/FA vacancies, undercoordinated Pb 2+ , and Pb I antisites) at the surface and interface of the perovskite. [24][25][26] Those defects always act as non-radiative recombination Formamidinium methylammonium lead iodide (FAMAPbI 3 ) perovskite has been intensively investigated as a potential photovoltaic material because it has higher phase stability than its pure FAPbI 3 perovskite counterpart. However, its power conversion efficiency (PCE) is significantly inferior due to its high density of surface detects and mismatched energy level with electrodes.…”

Mixed-Phase Low-Dimensional Perovskite-Assisted Interfacial Lead Directional Management for Stable Perovskite Solar Cells with Efficiency over 24%

“…In recent years, organic–inorganic halide perovskite materials with excellent optical capture capacity and carrier conductivity have been widely applied in solar cells, photodetectors, photosensitizer and light-emitting diodes. − Perovskite solar cells (PSCs), being the most studied among them, have achieved the satisfactory power conversion efficiency (PCE) of 25.5% . However, owing to the mixed cations and anions contained in perovskite materials, a large number of unfavorable defects would grow up after or during the annealing process, − which will undoubtably deteriorate the efficiency and stability, especially under the conditions of humidity, heat, and light. − …”

Deeper Insight into the Role of Organic Ammonium Cations in Reducing Surface Defects of the Perovskite Film

“…However, we notice that the BAI‐treated PSCs outperform the 3FBAI‐treated ones in terms of PCE and stability, which is unusual because the additional fluorine atoms in the 3FBAI are usually considered to more efficiently reduce the interfacial trap states and to enhance the hydrophobicity of perovskite film [28–31] . Some previous works have also indicated that increasing the F atoms in the OAS does not always favor the passivation effect [32, 33] . Hence, the passivation mechanism of OAS for the perovskite film in the presence of excess PbI 2 needs to be deeply understood to explain different performances of the PSCs with BAI and 3FBAI treatments.…”

“…[28][29][30][31] Some previous works have also indicated that increasing the F atoms in the OAS does not always favor the passivation effect. [32,33] Hence, the passivation mechanism of OAS for the perovskite film in the presence of excess PbI 2 needs to be deeply understood to explain different performances of the PSCs with BAI and 3FBAI treatments.…”