Grain Boundary Chemical Anchoring via Bidirectional Active Site Additive Enables Efficient and Stable Perovskite Solar Cells

Abstract

Since the first demonstration on all-solidstate perovskite solar cells (PSCs) with a power conversion efficiency (PCE) of 9.7%, [3] the PCE of the organometal halidebased PSCs has skyrocketed from initial 3.8% [4] to presently certified 25.7%, [5] which makes the PSCs a promising candidate for the next-generation solar cells. It is well known that efficient and stable PSCs require high quality perovskite films. However, a large number of defects exist on the surface and grain boundaries (GBs) of perovskite films prepared by solution method, which acting as nonradiative recombination sites, causing a significant reduction in photogenerated carrier lifetimes and concomitant drop of open-circuit voltage (V OC ). [6][7][8] In addition, the defects at GBs would make the penetration of water and oxygen easier, which facilitates the degradation of perovskites films. [9,10] To further enhance the device performance, it is highly expected to minimize the trap-assisted nonradiative recombination via reducing defects in perovskite films. [11] Currently, additive engineering is one of the effective methods commonly used for defect passivation in perovskite films. [12][13][14] Lewis acid molecules, [15,16] Lewis base molecules, [17][18][19] and organic/inorganic salts [20,21] have been introduced as additive toThe nonradiative recombination induced by trap states at the surface and grain boundaries impedes the further increase of power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Consequently, it is highly desirable to minimize the trap-assisted nonradiative recombination in perovskite films. Here, an effective additive engineering strategy is reported where N-succinimidyl 6-maleimidohexanoate (denoted as NSMH) with multiple active sites and hydrophobic alkyl chains were incorporated for fully eliminating undercoordinated Pb 2+ traps in perovskite films. It is revealed that improved crystallinity and reduced defect density are achieved, which is ascribed to the strong coordination interaction between the carbonyl groups at both sides of NSMH molecules and Pb 2+ . As a result, the NSMH-modified device exhibits a champion PCE of 22.40% with negligible hysteresis, which is significantly higher than 20.67% of the control device. The unencapsulated modified device exhibits no degradation while the control device degrades to 82% of its initial PCE after storing for 1536 h in a relative humidity of 10-20% at room temperature in the dark.

Buried Interface Regulation by Bio‐Functional Molecules for Efficient and Stable Planar Perovskite Solar Cells

“…Figure 1a shows that B 12 has multiple carbonyl and amino groups, which can simultaneously passivate the various trap sites of perovskite material, such as non‐coordinating Pb 2+ and neutral iodine, leading to strong regulation of the crystallization of perovskite film with lower trap density, preventing non‐radiative recombination, and enhancing charge carrier transport [2b,26] . A change in the binding energy of the Pb and I, presented in Figure S8a–b, provided more evidence for the B 12 ‐perovskite film interaction.…”

“…The built‐in potential ( V bi ) of the SnO 2 and the SnO 2 @B 12 ‐based device was further studied by measuring Mott‐Schottky curves [26] . Figure 5c shows that the V bi of that specific device is higher in comparison to that of the control device by 0.026 V, favoring the carrier separation, transport, and extraction processes.…”

Application of Natural Molecules in Efficient and Stable Perovskite Solar Cells

“…Furthermore, these defects are sensitive to environmental factors, such as moisture, oxygen, temperature, etc., affecting the optoelectronic properties of the perovskite, even leading to degradation. To solve these problems, many scientists have explored various strategies, such as additive engineering, [ 9 , 10 ] interface engineering, [ 11 , 12 , 13 ], and so on. Various materials with multiple functional groups have been used to assist these strategies.…”

Enhanced Perovskite Solar Cell Stability and Efficiency via Multi‐Functional Quaternary Ammonium Bromide Passivation

“…The method of low-dimensional perovskite passivation 3D perovskite has positive effect of improving the efficiency and stability of PSCs. [25][26][27][28][29][30][31] Even though the quality of the perovskite films were optimized by the reported effective passivation methods, but most of the optimization are conducted by single functional, and the optimized perovskite still suffers from the corrosion of the external environment (such as high humidity) directly. Therefore, it's time to develop suitable passivators with functional groups which not only for passivated defects, but also need external protective functional groups for resistance to environmentalThe Achilles heel of the perovskite solar cells (PSCs) is the long-term stability under working condition which restricts the commercialization.…”

“…Lewis acids and bases have been proven functional in bonding with uncoordinated halides or metal ions in the perovskite crystals to form Lewis adducts, thereby reducing the density of defects. [25][26][27] Ma et al introduced nicotinamide as a Lewis base additive into the perovskite precursor solution, which found that the nicotinamide in the perovskite film can passivate the surface and grain boundary defects, control the morphology of the film, and improve the crystallinity. [25] Wang et al evidenced that BA + can form a two-dimensional (2D) layered perovskite with a wide band gap upon the threedimensional (3D) perovskite.…”