Tailored Amphiphilic Molecular Mitigators for Stable Perovskite Solar Cells with 23.5% Efficiency

Abstract

Passivation of interfacial defects serves as an effective means to realize highly efficient and stable perovskite solar cells (PSCs). However, most molecular modulators currently used to mitigate such defects form poorly conductive aggregates at the perovskite interface with the charge collection layer, impeding the extraction of photogenerated charge carriers. Here, a judiciously engineered passivator, 4‐tert‐butyl‐benzylammonium iodide (tBBAI), is introduced, whose bulky tert‐butyl groups prevent the unwanted aggregation by steric repulsion. It is found that simple surface treatment with tBBAI significantly accelerates the charge extraction from the perovskite into the spiro‐OMeTAD hole‐transporter, while retarding the nonradiative charge carrier recombination. This boosts the power conversion efficiency (PCE) of the PSC from ≈20% to 23.5% reducing the hysteresis to barely detectable levels. Importantly, the tBBAI treatment raises the fill factor from 0.75 to the very high value of 0.82, which concurs with a decrease in the ideality factor from 1.72 to 1.34, confirming the suppression of radiation‐less carrier recombination. The tert‐butyl group also provides a hydrophobic umbrella protecting the perovskite film from attack by ambient moisture. As a result, the PSCs show excellent operational stability retaining over 95% of their initial PCE after 500 h full‐sun illumination under maximum‐power‐point tracking under continuous simulated solar irradiation.

Toward Efficient and Stable Perovskite Solar Cells: Choosing Appropriate Passivator to Specific Defects

“…[ 91 ] Organic ammonium salts have also been reported by Zhu et al to have similar functions. [ 139 ] They judiciously designed a new passivation molecule, 4 ‐ tert ‐butyl‐benzylammonium iodide (tBBAI) in Figure 9c, that significantly enhanced charge extraction from the perovskite film into hole transport layer (HTL), while suppressing carrier radiation‐less recombination. In addition, the hydrophobic tert ‐butyl resists the invasion of moisture, leading to better operational stability.…”

“…Reproduced with permission. [ 139 ] Copyright 2020, John Wiley and Sons. d) Chemical structures of BAA additives and schematic illustration of defect passivation and water repellence induced by BAA introduced.…”

Surface Passivation of Perovskite Film by Sodium Toluenesulfonate for Highly Efficient Solar Cells

“…Up to now several approaches have been developed to passivate the defects at the surface of perovskite film, including solvent annealing, additive engineering, post‐treatment, and surface modification . In particular, surface modification fulfilled by depositing a modifier layer atop the perovskite layer is facile with no need to change the fabrication process of the perovskite layer and thus has been extensively utilized . Toward this end, different types of modifiers have been developed; among them, organic salts containing ionic organic functional groups are particularly effective due to their high solubilities in organic solvents and facilities in tuning compositions by changing negative‐ or positive‐charged components .…”

TiO2 Colloid‐Spray Coated Electron‐Transporting Layers for Efficient Perovskite Solar Cells

“…Owing to its advantages (e.g., good transparency, favorable bandgap edge positions in relation to perovskites, environmental stability, and the feasibility of the solution processing with low-fabrication costs), TiO 2 has been widely adopted for the fabrication of high-efficiency PSCs. [9][10][11][12][13][14] An additional layer of thin mesoporous TiO 2 (mp-TiO 2 ) has been generally used to compensate the deficient charge collection efficiency, since of PSCs) by spray coating. Most spray coating for the deposition of inorganic ETLs is done using SnO 2 nanoparticles, but the maximum efficiency is still less than 20%.…”