Surface Reconstruction for Efficient Cs₂AgBiBr₆ Solar Cells

Abstract

Lead-free double perovskite Cs 2 AgBiBr 6 is considered to serve as a substitute for toxic lead-based perovskite components and is a promising candidate for environmentally friendly perovskite solar cells (PSCs). However, the high deep-level trap density in Cs 2 AgBiBr 6 films hinders the device performance, which is caused by the different solubilities of components in the precursor solution and the solutionprocess fabrication method. In this work, we reported a surface reconstruction (SR) strategy, in which a dissolution process is initiated by dimethyl sulfoxide (DMSO) and followed by the introduction of methylammonium bromide (MABr) to generate a mixed organic− inorganic intermediate phase and induce an orderly recrystallization. The dissolution−recrystallization process effectively improves the overall crystalline quality and surface composition stoichiometry ratio, passivates the bromine vacancies enriched in the film, and forms a dense as well as ordered film surface, resulting in reduced trap density, extended carrier lifetime, better interfacial contact, and faster carrier extraction. The differences in underlying mechanisms and effects between the conventional interfacial passivation (IP) strategy based on the passivator/isopropanol (IPA) system and the SR strategy proposed in this work were also compared by multiple characterizations. All these advantages enable the Cs 2 AgBiBr 6 -based PSCs fabricated by the SR strategy to achieve a significantly higher power conversion efficiency (PCE) of 2.05% and an ultrahigh fill factor (FF) of 83.80% as well as open-circuit voltage (V OC ) of 1.201 V, with good stability and broad applicability in the hole transport layer (HTL)-free PSCs. Therefore, this work points out the fundamentally different mechanisms of two post-treatment strategies on the overall regulation of Cs 2 AgBiBr 6 films and provides a clear clue to further enhance the quality of lead-free double perovskite films and optimize the photovoltaic performance of PSCs.

From particles to films: production of Cs2AgBiBr6-based perovskite solar cells and enhancement of cell performance via ionic liquid utilization at the TiO2/perovskite interface

“…In the majority of studies in the literature, the PL emission peak of Cs 2 AgBiBr 6 was broad and centered around 600–650 nm due to the domination of the PL spectra with indirect bandgap recombination. 39,44,45 However, in our case, the sample without the IL exhibited three emission peaks at ∼536, 606, and 676 nm. While the PL peak at 536 nm (2.31 eV) originated from the direct band gap emission of Cs 2 AgBiBr 6 , the other two emission peaks at 606 nm (2.04 eV) and 676 nm (1.83 eV) were indicative of phonon-assisted indirect band transitions, as observed in previous literature studies.…”

Passivating A-Site and X-Site Vacancies Simultaneously via N-Heterocyclic Amines for Efficient Cs2AgBiBr6 Solar Cells

“…The double-perovskite Cs 2 AgBiBr 6 , highly stable due to its high positive decomposition energy, is considered to be another promising candidate . Since the first report on Cs 2 AgBiBr 6 solar cells in 2017, many attempts have been made to optimize the optoelectronic properties of Cs 2 AgBiBr 6 PSCs, including using low-pressure assistance, , modulating the stoichiometric precursor ratio, , adding organic interface layers, changing charge transport layers, − and employing inverted device structures . So far, the highest PCE achieved for the Cs 2 AgBiBr 6 PSC is 6.4%, managed by using a hydrogenation method to narrow its band gap …”

Breaking the bottleneck of lead-free perovskite solar cells through dimensionality modulation

“…29,30 In addition, their relatively large bandgap for single-junction PSCs and indirect bandgap are also detrimental to solar energy harvesting. 31–34…”