Stiffening the Pb-X Framework through a π-Conjugated Small-Molecule Cross-Linker for High-Performance Inorganic CsPbI₂Br Perovskite Solar Cells

Abstract

Inorganic CsPbI 2 Br perovskites have witnessed incredible advances as a promising representative for translucent and tandem solar cells, but unfortunately, they are still plagued by serious energy losses and undesired phase instability. Herein, a new type of π-conjugated small molecule of 4-guanidinobenzoic-acidhydrochloride (4-GBACl) is demonstrated to effectively cross-link the Pb-X framework of perovskites. The strong coordination between 4-GBACl and the [PbX 6 ] 4− octahedron of perovskites effectively stiffens the Pb-X framework to suppress the ion migration, thus stabilizing the perovskite phase structure against light and thermal conditions. Apart from the physical barrier for phase instability resulting from the hydrophobic benzene ring at grain boundaries (GBs), guanidinium cations and −COOH and Cl − groups can simultaneously afford the passivation of positively and negatively charged defects at the GBs and surface, including undercoordinated halide species and undercoordinated Pb 2+ ions, thereby effectively inhibiting the charge trapping/recombination centers. Two-dimensional confocal-fluorescence mapping images provide a visualized sight into the significantly suppressed nonradiative recombination and the prolonged carrier lifetime. It is suggested that the 4-GBACl additive plays multiple roles in grain cross-linking to regulate crystallization, distinctly reducing the trapstate density, ion migration inhibition, and moisture barrier in CsPbI 2 Br films. Consequently, the 4-GBACl-treated device exhibits a champion power conversion efficiency (PCE) of 15.59% accompanied with a considerably improved V oc of 1.28 V and maintains 88% of the initial PCE value after 1200 h aging under 20% relative humidity.

Consolidating a Pb–X framework via multifunctional passivation with fluorinated zwitterions for efficient and stable perovskite solar cells

“…In addition, strong interactions between D-PFPAA and the perovskite could increase the energy barrier to [PbX 6 ] 4− octahedral rotation, consolidating the Pb–X framework and thus enhancing the stability toward humidity. 13…”

“…7–12 More seriously, the existence of lots of ionic defect states can lead to ion migration and can catalyze the rotational distortion of [PbX 6 ] 4− octahedrons, subsequently accelerating the degradation of the entire perovskite film under the influence of external stress factors, such as oxygen, moisture, light, and heat. 13–17…”

“…[7][8][9][10][11][12] More seriously, the existence of lots of ionic defect states can lead to ion migration and can catalyze the rotational distortion of [PbX 6 ] 4À octahedrons, subsequently accelerating the degradation of the entire perovskite lm under the inuence of external stress factors, such as oxygen, moisture, light, and heat. [13][14][15][16][17] Defect passivation is considered to be an effective strategy for mitigating trap-assisted recombination and enhancing the performance of PSCs. [18][19][20][21] Therefore, various passivators have been introduced to passivate defects, including Lewis base/acid molecules, inorganic salts, polymers, zwitterions, etc.…”

Enhanced photostability of CsPbI2Br-based perovskite solar cells through suppression of phase segregation using a zwitterionic additive

“…[17][18][19][20][21][22] Using this approach, a wide variety of organic compounds, such as organic ammonium salts, [23][24][25][26][27] amino acids, 28,29 ionic liquids, 30,31 p-conjugated polymers, 32,33 etc. 34,35 have been explored as stabilizing agents for CsPbI 2 Br. However, the vast majority of research was focused on exploring the effect of modication of the CsPbI 2 Br absorber on the stability of the lms or solar cells with respect to humidity in an ambient environment or thermal stress (see examples in Table S1, ESI †), and insufficient attention was paid to the study of the photostability of the modied materials, 23,35 which complicates the assessment of the possibility of their application under real solar cell operating conditions taking into account the propensity of CsPbI 3Àx Br x absorbers to light-induced phase segregation.…”

Stable High‐Efficiency CsPbI2Br Solar Cells by Designed Passivation Using Multifunctional 2D Perovskite

“…More important, the strong interaction between 2D and 3D perovskite can also stiffen the corner-sharing [PbX 6 ] 4− octahedron network to stabilize the α-phase CsPbI 2 Br. [42,43] All together, the Gly-I additive plays multiple roles in regulating the crystallization process, passivating defect states, and stabilizing the phase structure of the CsPbI 2 Br perovskite.…”