Intermolecular π–π Conjugation Self‐Assembly to Stabilize Surface Passivation of Highly Efficient Perovskite Solar Cells

Abstract

Surface passivation is an effective approach to eliminate defects and thus to achieve efficient perovskite solar cells, while the stability of the passivation effect is a new concern for device stability engineering. Herein, tribenzylphosphine oxide (TBPO) is introduced to stably passivate the perovskite surface. A high efficiency exceeding 22%, with steady‐state efficiency of 21.6%, is achieved, which is among the highest performances for TiO2 planar cells, and the hysteresis is significantly suppressed. Further density functional theory (DFT) calculation reveals that the surface molecule superstructure induced by TBPO intermolecular π–π conjugation, such as the periodic interconnected structure, results in a high stability of TBPO–perovskite coordination and passivation. The passivated cell exhibits significantly improved stability, with sustaining 92% of initial efficiency after 250 h maximum‐power‐point tracking. Therefore, the construction of a stabilized surface passivation in this work represents great progress in the stability engineering of perovskite solar cells.

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“…In agreement with the FTIR results (Figure 3 g), the O atom of C=O group in QA is anchored to the exposed Pb atom with bond length of 3.04 Å. Moreover, the characteristics of electron loss are observed on H atoms of benzyl group close to MAPbI 3 surface indicating the Coulomb interaction between H and I [5] . This interaction might help suppress the evaporation of iodine in MAPbI 3 during annealing process.…”

“…Interestingly, the characteristic stretching vibration of the C=O in QA shifted from 1625 cm −1 to about 1616 cm −1 upon deposition on the MAPbI 3 thin film [46] . This shift may be the result of a O⋅⋅⋅Pb coordination bonding via Lewis base–acid interaction between the C=O bond of QA and Pb 2+ in the MAPbI 3 thin film [5, 13] . The FTIR spectra for PbI 2 and QA treated PbI 2 were recorded to further verify this hypothesis (Supporting Information, Figure S7).…”

“…Thanks to relentless efforts in materials development and devices engineering, remarkable progress has been achieved over the last decade with the power conversion efficiencies (PCEs) improved from around 4 % to more than 25 % for single junction devices [3, 4] . However, long‐term stability is widely considered to be one of the major challenges that must be addressed before large scale commercialization of PSCs [5, 6] . Many approaches have been developed during last few years in improving the stability of PSCs, including surface passivation of halide perovskite thin films using various types of materials, such as organic halide salts, [2, 7, 8] polymers, [9–11] organic small molecules, [5, 12–14] low‐dimensional perovskite hybrids, [15, 16] inorganic compounds, [17, 18] and many others [19, 20] .…”

“…While various types of materials have been developed as surface passivation agents, the long‐term stability requirements for the commercialization of PSCs is yet to be met by these materials. An ideal surface passivation agent should be easy to process, low cost, and highly stable [5, 13] …”

“…[3,4] However, long-term stability is widely considered to be one of the major challenges that must be addressed before large scale com-mercialization of PSCs. [5,6] Many approaches have been developed during last few years in improving the stability of PSCs,i ncluding surface passivation of halide perovskite thin films using various types of materials,s uch as organic halide salts, [2,7,8] polymers, [9][10][11] organic small molecules, [5,[12][13][14] lowdimensional perovskite hybrids, [15,16] inorganic compounds, [17,18] and many others. [19,20] Thef unction of surface passivation is mainly twofold.…”