Recent Progress in Ionic Liquids for Stability Engineering of Perovskite Solar Cells

Abstract

Perovskite solar cells attract widespread attention due to their impressive power conversion efficiencies, high absorption coefficients, tunable bandgap, and straightforward manufacturing protocols. However, in the process of further development and optimization toward mass production, the long‐term stability stands as one of the most urgent challenges that need to be overcome. Given the excellent thermal stability and high structural designability, ionic liquids (ILs) are relatively green room‐temperature molten salts that have been widely applied to perovskite photovoltaic devices with promising results in view of improved stability and enhanced device performance. In this review, the reasons and mechanisms of instability of such devices under external and internal factors are analyzed. The current strategies of ILs engineering for improved stability of the devices are classified and summarized, including the IL‐assisted perovskite film evolution and IL‐modified photophysical properties of the perovskite photoactive layer and the related stability and photovoltaic performance of the devices. The challenges that stand as obstacles toward further development of perovskite solar cells based on IL engineering and their prospects are also discussed.

Differentially Accelerated Electron and Hole Diffusion in MAPbI3 Film Surface Treated by a Quaternary Ammonium Halide for High‐Efficiency Solar Cells

“…As is well known, during the fabrication process of MAPbI 3 , defects such as MA + and I − vacancies form, especially on the surface and at the grain boundaries. [ 33 ] As proved in many previous studies, the quaternary ammonium groups have the unique ability to form hydrogen bonds with the halide ions and can be easily anchored in perovskite materials. Thus, during treatment using TEAI solution which contains abundant TEA + cations and I − anions, the TEA + cations will substitute partial MA + cations on the surface of MAPbI 3 , forming TEAPbI 3 , and fill the MA + vacancies at the same time, making the negatively charged defects effectively passivated, as shown in Figure 5 .…”

“…Meanwhile, the I À vacancies can also be compensated by the I À anions from the TEAI solution. [12,33] Considering that in perovskites the defect trapping or scattering is the main factor that restricts carrier diffusion, after defect passivation, the carrier diffusivity should be enhanced. Furthermore, in organic-inorganic hybrid lead iodide perovskites such as MAPbI 3 and FAPbI 3 , the inorganic corner-shared PbI 6 octahedra build up a framework, with the organic molecular cations embedded in.…”

Solvent Engineering of Ionic Liquids for Stable and Efficient Perovskite Solar Cells

“…The exciting thing is that equally effective applications of ILs occur in the perovskite field, including PSCs, [ 49,50 ] perovskite light‐emitting diodes, [ 51 ] and perovskite photodetectors. [ 51 ] In particular, the additive engineering, [ 52–54 ] interface engineering, [ 55,56 ] and stability engineering [ 57,58 ] of ILs in PSCs have significantly promoted the development of high‐efficiency devices. Unlike organic ferroelectric materials, [ 59 ] 2D materials, [ 60 ] organic semiconductors, [ 61 ] and organic salt [ 62 ] are applied singularly in interfacial or additive engineering for regulating the crystallization of perovskite film, the designability of chemical structures of ILs and the existence of hydrogen bonds as well as electrostatic network provided by cation and anion in ILs have prompted the same attention to ILs in solvent engineering to replace the toxic ones for improving the crystallization process with high quality perovskite film.…”

Dimethylammonium Cation-Induced 1D/3D Heterostructure for Efficient and Stable Perovskite Solar Cells

“…Despite inspiring development in past decades, the application of PSCs is severely restricted because of their poor stability against moisture, heat, and UV light, attributed to the inherent structural characteristics of conventional (three dimensional) perovskites [ 13 , 14 , 15 , 16 ]. To be specific, inevitable defects which form during fabrication process of PSCs and are located at grain boundaries and interfaces can not only serve as the center of trap-assisted non-radiative recombination, but also induce the decomposition of perovskite films in humid conditions and consequently decrease the efficiency and long-term stability of PSCs [ 17 , 18 , 19 , 20 , 21 , 22 ]. On the other hand, their severe toxicity is a potential threat to the environment and humankind [ 23 ].…”