Universal Surface Passivation of Organic–Inorganic Halide Perovskite Films by Tetraoctylammonium Chloride for High-Performance and Stable Perovskite Solar Cells

Abstract

The power conversion efficiency (PCE) of perovskite solar cells has been showing rapid improvement in the last decade. However, still, there is an unarguable performance deficit compared with the Schockley–Queisser (SQ) limit. One of the major causes for such performance discrepancy is surface and grain boundary defects. They are a source of nonradiative recombination in the devices that not only causes performance loss but also instability of the solar cells. In this study, we employed a direct postsurface passivation strategy at mild temperatures to modify perovskite layer defects using tetraoctylammonium chloride (TOAC). The passivated perovskite layers have demonstrated extraordinary improvement in photoluminescence and charge carrier lifetimes compared to their control counterparts in both Cs0.05(FAPbI3)0.83(MAPbBr3)0.17 and MAPbI3-type perovskite layers. The investigation on electron-only and hole-only devices after TOAC treatment revealed suppressed electron and hole trap density of states. The electrochemical study demonstrated that TOAC treatment improved the charge recombination resistance of the perovskite layers and reduced the charge accumulation on the surface of perovskite films. As a result, perovskite solar cells prepared by TOAC treatment showed a champion PCE of 21.24% for the Cs0.05(FAPbI3)0.83(MAPbBr3)0.17-based device compared to 19.58% without passivation. Likewise, the PCE of MAPbI3 improved from 18.09 to 19.27% with TOAC treatment. The long-term stability of TOAC-passivated perovskite Cs0.05(FAPbI3)0.83(MAPbBr3)0.17 devices has retained over 97% of its initial performance after 720 h in air.

Surface Capping Layer Prepared from the Bulky Tetradodecylammonium Bromide as an Efficient Perovskite Passivation Layer for High-Performance Perovskite Solar Cells

“…The FTO was cleaned and SnO 2 was prepared following the literature procedure. 27 Then, the substrate was transferred to a nitrogen glove box (O 2 and H 2 O are <0.01 ppm) to spin-coat perovskite, TDDAB, and spiro-OMeTAD layers.…”

“…The mixed perovskite was spin-coated at 1000 rpm for 10 s and 6000 rpm for 20 s, followed by chlorobenzene dripping in the last 5 s. Subsequently, the film was annealed at 100 °C for 1 h. Next, various concentrations of TDDAB in 2-propanol were deposited on the perovskite film following the literature procedure. 27 The optimized TDDAB concentration for the champion solar cell was 2 mM. Afterward, spiro-OMeTAD and Au (∼70 nm) were successively deposited following the procedure described in the literature procedure.…”

“…Afterward, spiro-OMeTAD and Au (∼70 nm) were successively deposited following the procedure described in the literature procedure. 27 XRD Film Preparation. To study the interaction of PbI 2 and TDDAB, PbI 2 /TDDAB (1:1 molar ratio) and PbI 2 /TDDAB (1:2 molar ratio) were mixed in DMF/DMSO (4:1 v/v) at 70 °C for 30 min.…”

“…27,28 Similarly, I−V and EQE of the devices characterized following the conditions provided in reference, where the aperture area of the cell is 0.1 cm 2 . 27,28 ■…”

“…FTO substrates and all chemicals used in this study are obtained from the same company in our previous report. 27 TDDAB was purchased from Sigma-Aldrich.…”