Zwitterionic Ionic Liquid as Additive for High‐Performance FAPbI₃ Perovskite Solar Cells with Negligible Hysteresis

Abstract

Imidazolium‐based ionic liquids have been established as promising candidates for additives in perovskite solar cells. Herein, 1‐(1‐ethyl‐3‐imidazolium)propane‐3‐sulfonate (EIMS) zwitterionic ionic liquid is studied as additive to enhance the performance of the FAPbI3 perovskite solar cells. The addition of EIMS leads to the generation of porous PbI2 film, which promotes the reaction of PbI2 with FAI solution and thus improves the quality of FAPbI3 perovskite film during the two‐step sequential spin coating. It is revealed that EIMS accelerates the extraction of electron, inhibits the formation of pinhole, and reduces the defect density, which leads to an increased efficiency of 22.1%. The hysteresis index is also reduced from 0.142 to 0.009, which indicates the addition of EIMS can realize a negligible hysteresis behavior in the solar cells. Moreover, devices prepared with EIMS retain above 96% of the original power conversion efficiency (PCE) value after being stored in dry air for 45 days. All these results demonstrate that the imidazolium‐based zwitterionic ionic liquid additive strategy is a promising way for high‐performance perovskite solar cells.

Designing a Novel Hole-Transporting Layer for FAPbI3-Based Perovskite Solar Cells

“…The hole-transporting layer (HTL) in PSCs is a vital part of the device framework. The HTL is commonly positioned in the intermediate region between the PVSK and the upper electrode. , It is responsible for facilitating the transportation of positively charged carriers, commonly referred to as “holes”, that are generated through the absorption of sunlight toward the electrodes. , The HTL offers the responsibility of altering the energy-level alignment and interfacial characteristics at the interface between the PVSK and the HTL . This alteration contributes to the attainment of desirable energy level variation, thus allowing the effective extraction of charges and minimizing charge losses at the interface.…”

“…The HTL is commonly positioned in the intermediate region between the PVSK and the upper electrode. 25,26 It is responsible for facilitating the transportation of positively charged carriers, commonly referred to as "holes", that are generated through the absorption of sunlight toward the electrodes. 27,28 The HTL offers the responsibility of altering the energy-level alignment and interfacial characteristics at the interface between the PVSK and the HTL.…”

Notable Performance Enhancement of CsPbI2Br Solar Cells by a Dual-Function Strategy with CsPbBr3 Nanocrystals

“…At low voltage, the dark current−voltage (I− V) curve is linear, reflecting the Ohmic response. In the trapfilled limited (TFL) region, I increases nonlinearly with V. 47 can be estimated according to n t = 2ε 0 εV TFL /(eL 2 ), 48 where ε 0 , ε, and e are the vacuum permittivity, relative dielectric constant, and the elementary charge, V TFL is the TFL voltage, and L is the thickness of the perovskite layer that is estimated from Figure S17. After the CsPbBr 3 NC treatment, n t reduces to 1.83 × 10 15 from 3.81 × 10 15 cm −3 , solidly supporting the discussion regarding E u .…”

Recent advances in ionic molecules applied in perovskite solar cells

“…Besides the precursor additive in one-step perovskite fabrication, Li et al doped an imidazolium sulfonate zwitterion EIMS into the PbI 2 solution for the two-step sequential deposition of FAPbI 3 films. 126 The strong interaction between the sulfonate groups in EIMS and Pb 2+ cations in the solutions led to the formation of porous PbI 2 films after thermal annealing, facilitating the diffusion of FAI solution into the PbI 2 films, and thus the reaction between them became more complete and perovskite films with slightly larger grain sizes and less pinholes were prepared. Yuan et al introduced another sulfonate-based additive, KHFDF, in the PbI 2 precursor, which exhibited similar functions of retarding the PbI 2 crystallization in the two-step fabrication process.…”