Efficient and Stable Perovskite Solar Cells by Fluorinated Ionic Liquid–Induced Component Interaction

Abstract

Because of the high absorption coefficient, [1] extra-long carrier diffusion lengths, [2] excellent optoelectronic properties, [3] single junction organic halide perovskite solar cells (PSCs) have attracted great attention, [4] as their certified power conversion efficiencies (PCEs) have experienced unprecedentedly rapid increase from 3.8% to 25.5% over the past decade. [5] Given the outstanding photovoltaic performance, PSCs have been treated as a promising candidate for next-generation high-performance solar cells, as compared with the conventional inorganic counterparts (silicon, CdTe, and so on) including the possibility for use in spacecrafts. [6] Despite impressive progress has been made in PSCs performance in the last few years, the instability issue of organic components in polycrystalline organic halide perovskites (OHPs) films is a limiting factor for industrial exploitations. [7] In general, the organic species in OHPs, such as methylamine (MA) and formamidine (FA), usually suffer from high volatility and instability during thermalannealing processes and/or under illuminations. [8] A high density of point defects is expected for the formation of MA þ vacancies in polycrystalline OHPs films. [7a] The monovalent cation vacancies leading to shallow trap states within the bandgap can act as charge recombination centers, which limit the photovoltaic performance of PSCs. [7b] Moreover, they are considered as the main reason for the degradation in OHPs films. [9] As a countermeasure, several strategies have been developed to tackle these

Ionic Liquids-Enabled Efficient and Stable Perovskite Photovoltaics: Progress and Challenges

“…This anchoring effect of the IL BMIBr suppresses the ion migration and loss of MA + from the perovskite film, leading to improved thermal stability of the film. Moreover, our group also demonstrated that the fluorinated IL methyl­ammonium difluoro­acetate (MA + DFA – ) can interact with MAPbI 3 perovskite to effectively improve its stability . Recently, Bai et al reported that introducing a small amount of the IL 1-butyl-3-methyl­imidazolium tetrafluoro­borate (BMIMBF 4 ) in MAPbI 3 perovskite (Figure d) could significantly improve the photovoltaic performance and long-term stability of PSCs.…”

“…Moreover, our group also demonstrated that the fluorinated IL methylammonium difluoroacetate (MA + DFA − ) can interact with MAPbI 3 perovskite to effectively improve its stability. 92 Recently, Bai et al 74 reported that introducing a small amount of the IL 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF 4 ) in MAPbI 3 perovskite (Figure 9d) could significantly improve the photovoltaic performance and long-term stability of PSCs. Through the XPS spectra of the perovskite film surface (Figure 9e) and time-of-flight secondary-ion mass spectrometry (ToF-SIMS) of the perovskite bulk (Figure 9f,g), it can be demonstrated that the anions and cations of BMIMBF 4 are not identically distributed in the perovskite film.…”

Grain Size and Interface Modification via Cesium Carbonate Post-Treatment for Efficient SnO2-Based Planar Perovskite Solar Cells

“…To improve the optoelectronic performance of PSCs, many efforts have been devoted such as exploiting novel charge transport materials, , composition engineering of perovskites, , interfacial modification, − and so on. SnO 2 has been considered as a promising ETL for PSCs because SnO 2 has a deeper conduction band than TiO 2 , faster electron mobility, and more favorable energy level alignment. , In our previous studies, morphologically regulated SnO 2 nanocrystals were synthesized for PSCs, which display improved electron transport because of their specially designed architectures. − However, defects and trap sites including Sn interstitials and O vacancies usually exist in SnO 2 nanocrystals, which are detrimental to electron transport and give rise to charge recombination .…”

Cost-Effective High-Performance Charge-Carrier-Transport-Layer-Free Perovskite Solar Cells Achieved by Suppressing Ion Migration

“…To further suppress the ion migration within the HTL-free PSCs and trilayer PSC, PFTeDA with 27 fluorine atoms and a carbonyl unit was introduced as an additive in the system (referred to as target in the following text). Organic molecules with carbonyl units have been introduced into the MAPbI 3 system for efficient ion migration suppression and defect passivation since they will locate at surface and grain boundaries due to the chelation between the noncoordinating lead and carbonyl unit. , The carbon fluorine bonds exhibit highly hydrophobic chemical properties which induce kinetic barriers that slow the ion migration of MA + /I – and intrusion of O 2 and H 2 O. ,, Thus, in this study, the incorporation of PFTeDA is designed for efficiently blocking the ion migration, passivating crystal defects, and enhancing overall device stability in the MAPbI 3 -based CTL-free PSCs. The cross-section SEM image of a HTL-free PSC can be found in Figure a, the perovskite film was compactly coated on the FTO/SnO 2 substrate, and the carbon electrode was densely deposited on top of the perovskite light absorber.…”

“…Organic molecules with carbonyl units have been introduced into the MAPbI 3 system for efficient ion migration suppression and defect passivation since they will locate at surface and grain boundaries due to the chelation between the noncoordinating lead and carbonyl unit. 46,47 The carbon fluorine bonds exhibit highly hydrophobic chemical properties which induce kinetic barriers that slow the ion migration of MA + /I − and intrusion of O 2 and H 2 O. 46,48,49 Thus, in this study, the incorporation of PFTeDA is designed for efficiently blocking the ion migration, passivating crystal defects, and enhancing overall device stability in the MAPbI 3 -based CTL-free PSCs.…”