Acetic Acid Assisted Crystallization Strategy for High Efficiency and Long‐Term Stable Perovskite Solar Cell

Abstract

Improving the quality of perovskite poly‐crystalline film is essential for the performance of associated solar cells approaching their theoretical limit efficiency. Pinholes, unwanted defects, and nonperovskite phase can be easily generated during film formation, hampering device performance and stability. Here, a simple method is introduced to prepare perovskite film with excellent optoelectronic property by using acetic acid (Ac) as an antisolvent to control perovskite crystallization. Results from a variety of characterizations suggest that the small amount of Ac not only reduces the perovskite film roughness and residual PbI2 but also generates a passivation effect from the electron‐rich carbonyl group (CO) in Ac. The best devices produce a PCE of 22.0% for Cs0.05FA0.80MA0.15Pb(I0.85Br0.15)3 and 23.0% for Cs0.05FA0.90MA0.05Pb(I0.95Br0.05)3 on 0.159 cm2 with negligible hysteresis. This further improves device stability producing a cell that maintained 96% of its initial efficiency after 2400 h storage in ambient environment (with controlled relative humidity (RH) <30%) without any encapsulation.

Origin of High Efficiency and Long-Term Stability in Ionic Liquid Perovskite Photovoltaic

“…The peak of the Pb-O bond can further be observed in Raman spectrum of the PbI 2 -MAAc film (Figure S17 ). These results confirm the strong interaction between undercoordinated Pb 2+ and O atom in Ac − , which are consistent with previous reports that the Lewis base site C=O group can provide an electron pair to the undercoordinated Pb 2+ in the perovskite, thereby effectively passivating the perovskite film [ 7 , 38 ]. Together with the hydrogen bonds, therefore, the diagram of grains and GBs of MAAc perovskites can be drawn in Figure 4(e) , in which the MAAc at GBs stabilized by intrinsic hydrogen bonding between MA + and Ac − can anchor perovskite octahedron through Pb-O (undercoordinated Pb 2+ of MAPbI 3 and C=O of MAAc), N-H⋯I (MA + of MAAc and I − of MAPbI 3 ), and N-H⋯O (MA + of MAPbI 3 and C-O of MAAc), which can effectively stabilize the structure of perovskite and inhibit defects [ 7 , 28 ].…”

“…We dissolved PbI 2 into the MAAc solvent and investigated the characteristics of powders obtained from the PbI 2 -MAAc films. As shown in Figure S15 , the C=O vibration peak (1604.51 cm −1 ) in the PbI 2 -MAAc powder shifted to a low wavenumber as compared to C=O (1645.23 cm −1 ) in the pure MAAc, which is attributed to the coordination interaction between C=O of MAAc and undercoordinated Pb 2+ (I − vacancy) in the PbI 2 -MAAc films [ 38 ]. Moreover, we found that the position of Pb 2+ (4f 5/2 , 4f 7/2 ) in the PbI 2 -MAAc film has tendency towards lower binding energy relative to the PbI 2 -DMF film in the X-ray photoelectron spectroscopy (XPS) spectra (Figure S16 ).…”

High‐Performance Inverted Perovskite Solar Cells with Operational Stability via n‐Type Small Molecule Additive‐Assisted Defect Passivation

“…The Y-Th2 chelated the Pb 2+ ions in perovskite, hydrophobically modified its surface, and immobilized the A-site cations (see Scheme 1). As evidenced in the blue-shifted X-ray photoelectron spectroscopy (XPS) spectra of Pb 4f at 138.7 eV and 142.8 eV and Fouriertransform infrared spectroscopy (FT-IR) spectra around 1700 cm −1 (Figure S2, Supporting Information), [33] the carbonyl functional groups of the rhodanine terminal moieties of Y-Th2 chelated with the uncoordinated Pb 2+ , passivating the defect sites of perovskite. The hydrophobicity of Y-Th2, conferred by a combination of its hydrocarbon side chains and its rigid conjugated backbone, is expected to mitigate the moisture infiltration of the perovskite.…”

Perovskite Passivation Strategies for Efficient and Stable Solar Cells

“…The volatile FAAc that is obtained in the perovskite crystallization process can inhibit the degradation of perovskite. [151] A small amount of Ac reduces the roughness of the Figure 11. a) Schematic diagram and TEM image of the perovskite layer interface.…”

“…The volatile FAAc that is obtained in the perovskite crystallization process can inhibit the degradation of perovskite. [ 151 ] A small amount of Ac reduces the roughness of the perovskite film and the amount of residual PbI 2 , and it also generates a passivation effect with the electron‐rich carbonyl group (CO). Zhang et al showed that the 4‐aminobenzoic acid (ABA) as a nonvolatile additive could bridge the adjacent CsPbI 2 Br.…”