Dual-Interface Modification with BMIMPF₆ for High-Efficiency and Stable Carbon-Based CsPbI₂Br Perovskite Solar Cells

Abstract

The interface closely related to carrier transport plays a vital role in high-performance perovskite solar cells (PSCs). In this work, an ionic liquid (IL) 1-butyl-3-methylimidazole hexafluorophosphate (BMIMPF 6 ) has been introduced to simultaneously modify the TiO 2 and perovskite films, which improves the energy level matching and contact of the TiO 2 / CsPbI 2 Br interface as well as provides perovskite films with larger grain size, leading to more faster charge transfer and lower energy loss. Furthermore, the BMIMPF 6 modifier passivates the perovskite film defects and reduces defect-induced charge trapping and recombination in CsPbI 2 Br PSCs. Under dual-interface modification, the open-circuit voltage of the modified device increased to 1.22 V, and the power conversion efficiency (PCE) increased from 10.65 to 13.19%. Moreover, the unencapsulated modified devices exhibit an enhanced stability and maintain 91% of their initial PCE after 60 days of storage. This work has provided a strategy for efficient and stable PSCs by exploiting an IL to optimize the dual-interface at the same time.

How the ionic liquid BMIMBF4 influences the formation and optoelectronic properties of MAPbI3 thin films

“…While all 19 F NMR spectra (Fig. 5b) exhibit the typical double peak for BF 4 À due to the coexistence of the boron isotopes 10 BMIM + cation of the IL is probed. The 1 H signals of the alkyl region of the BMIM + also exhibit a characteristic shi, reversed to the observations in the 19 F spectra: while no shi is observed for pure MAI + IL solutions compared to pure IL, the signals are upeld-shied in pure PbI 2 and MAPbI 3 precursor solutions (Fig.…”

“…[3][4][5][6][7][8] A more recent key development to improve the efficiency and the stability of perovskite solar cells is the usage of passivating additives to reduce the number of defect states in the perovskite grain boundaries or at its interface to the charge extraction layers. This is either achieved by introducing passivating layers below and on top of the perovskite layer, [9][10][11][12][13][14] or by mixing different types of additives into the precursor solution. [15][16][17][18][19][20][21] The advantage of the latter approach is that the passivating effect is not limited to the interface, but also improves the perovskite grain boundary properties.…”

“…For this bifunctional passivation approach of MHPs, ionic liquids (IL) have turned out to be especially suitable. 10,[22][23][24][25] For example, Snaith et al mixed 1-butyl-3-methylimidazoliumtetrauoroborate (BMIMBF 4 ) into the precursor solutions of different halide perovskites, which lead to an extraordinary high stability of resulting solar cells and improved optoelectronic lm properties. 26 Another important aspect affecting the optoelectronic properties of perovskites is their morphology, which in turn is decisively determined by the exact crystallization processes that occur during the solution based thin lm preparation.…”

“…For this bifunctional passivation approach of MHPs, ionic liquids (IL) have turned out to be especially suitable. 10,22–25 For example, Snaith et al mixed 1-butyl-3-methylimidazoliumtetrafluoroborate (BMIMBF 4 ) into the precursor solutions of different halide perovskites, which lead to an extraordinary high stability of resulting solar cells and improved optoelectronic film properties. 26…”

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

“…As a consequence, the corresponding BMIMBF 4 ‐treated PSCs acquired stability by retaining 86.9% of the original PCE over 1000 h in N 2 atmosphere and 82% of the original PCE after 500 h in 35% RH (Figure 4e). Similarly, BMIM‐based IL 1‐butyl‐3‐methylimidazole hexafluorophosphate (BMIMPF 6 ) was used as interface modification layer that is located on the interface of the perovskite layer and the TiO 2 layer for improvement of the device stability by Yin et al [ 73 ] The interface modification of the IL BMIMPF 6 played an important role in the passivation of perovskite film defects and optimization of the contact of the TiO 2 /CsPbI 2 Br interface.…”