钙钛矿和SnO2薄膜表面的埋底界面上存在大量的缺陷，这些缺陷会阻碍载流子的提取，导致界面电荷积累和界面非辐射复合，而能级匹配不理想也会导致较低的界面载流子提取效率。

鉴于此，重庆大学陈江照研究员和中国科学技术大学杨上峰教授等人报道了一种有效的离子液体分子修饰SnO2/钙钛矿埋底界面的策略，并揭示了一种依赖于阳离子诱导空间位阻的异常阴离子钝化埋底界面缺陷的机制。

通过调节离子液体中有机阳离子的尺寸来调控空间位阻效应，适当弱化离子液体中阴、阳离子之间的相互作用力，从而增强阴离子与钙钛矿层和电子传输层之间的化学作用强度，最大化降低界面缺陷密度和改善界面能带排列。BAIMBF4修饰埋底界面后，电源转换效率从21.54%提高到23.61%，稳定性也获得了大幅提升。

Fig. 1.(a) Molecular structures and electrostatic potentials map of EMIMBF4, DCHIMBF4 and BAIMBF4. The ILs exhibit similar molecular structures, but have different sizes of cations (steric hindrance: BAIMBF4> DCHIMBF4 > EMIMBF4). (b) Schematically illustrated diagram of defect passivation by BAIMBF4. Optimized structures of defective SnO2 surface with (c) EMIMBF4, (d) DCHIMBF4, and (e) BAIMBF4. Optimized structures of defective FAPbI3surface with (f) EMIMBF4, (g) DCHIMBF4, and (h) BAIMBF4.

Fig. 2.XPS spectra of the pristine and treated SnO2 films with EMIMBF4, BAIMBF4 and DCHIMBF4: (a) Sn 3dspectra and (b) F 1sspectra. (c)FTIR spectra of the pristine and modified SnO2films. (d) 19F NMR spectra of pure BAIMBF4 and mixture of BAIMBF4+SnO2. (e) Pb 4f XPS spectra of the perovskite films without or with EMIMBF4, DCHIMBF4 and BAIMBF4. (Since the measurement depth of XPS is very limited, EMIMBF4, DCHIMBF4 and BAIMBF4 were dissolved in perovskite solution.) (f)19F NMR spectra of pure BAIMBF4 and mixture of BAIMBF4+PbI2.

Fig. 3.2D GIWAXS patterns of the (a) control and modified perovskite films with (b) EMIMBF4, (c) DCHIMBF4and (d)BAIMBF4. Dark I-V curves of the devices with the structure of (e) ITO/perovskite/Au, (f) ITO/ EMIMBF4/perovskite, (g) ITO/DCHIMBF4/perovskite and (h)ITO/ BAIMBF4/perovskite. PL mapping images of the perovskite films deposited on non-conductive glass (i) without or with the modification of (j) EMIMBF4, (k) DCHIMBF4 and(l) BAIMBF4.

Fig. 4.Transient reflection kinetics for the perovskite films deposited on (a)SnO2 and (b) SnO2-BAIMBF4ETLs. (c) SSPL and (d) TRPL spectra of the perovskite films prepared on the SnO2layers without and with EMIMBF4, DCHIMBF4 and BAIMBF4. (e) TPC and (f) TPV decay curves of the devices without or with ILs modification. (g) VOC versus light intensity for the devices with or without ILs modification. (h) Nyquist plots of the devices with or without ILs modification measured at a bias of 0.80 V in the dark. (i) Energy band diagram of all device components.

Fig. 5.Statistical distribution diagram of (a) JSC, (b) VOC, (c) FF and (d) PCE for the devices without and with EMIMBF4, DCHIMBF4 and BAIMBF4modification. The data were obtained from 20 individual cells. J-Vcurves of the champion devices (e) without and with (f) EMIMBF4, (g) DCHIMBF4 and (h) BAIMBF4 modification. Steady-state (i) current density and (j) PCE as a function of time for the champion control and ILs-modified devices measured at the maximum power point.

Fig. 6.(a) Moisture stability of the unencapsulated devices modified without and with ILs aged under a relative humidity of 10%-20% at room temperature in the dark. (b) Light stability of the unencapsulated devices modified without and with ILs under illumination of 100 mW/cm2 provided by white light LED at room temperature in the nitrogen-filled glovebox. (c) Thermal stability of the unencapsulated devices modified without and with ILs kept at 60 ℃ in a nitrogen-filled glovebox in the dark.

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