Sacrificial Agent Gone Rogue: Electron-Acceptor-Induced Degradation of CsPbBr₃ Photocathodes

Abstract

Lead halide perovskites (LHPs) have emerged as perspective materials for light harvesting, due to their tunable band gap and optoelectronic properties. Photocatalytic and photoelectrochemical (PEC) studies, employing LHP/liquid junctions, are evolving, where sacrificial reagents are often used. In this study, we found that a frequently applied electron scavenger (TCNQ) has dual roles: while it leads to rapid electron transfer from the electrode to TCNQ, enhancing the PEC performance, it also accelerates the decomposition of the CsPbBr 3 photoelectrode. The instability of the films is caused by the TCNQ-mediated halide exchange between the dichloromethane solvent and the LHP film, during PEC operation. Charge transfer and halide exchange pathways were proposed on the basis of in situ spectroelectrochemical and ex situ surface characterization methods, also providing guidance on planning PEC experiments with such systems.

A Tunable Electrochemical Strategy toward an All-Inorganic CsPbBr3 Perovskite

“…In general, this work has shown a strategy to synthesize CsPbBr 3 with an electrochemical substrate (PbO 2 ) that has fewer problems that those of conventional chemical–mechanical methods. Hopefully, it can facilitate relevant research on CsPbBr 3 , a widely applied perovskite due to its own advantages in various fields (solar cells, photodetectors, photocatalysis, lasers, light-emitting diodes, and resistive switching memories). − More importantly, it has shown a high tunability to synthesize perovskites of different contents with different optoelectronic properties, with even wider prospects in different types of applications, such as in two-terminal tandem solar cells, photodetectors in the fields of imaging and optical communication (such as MAPbI 2.55 Br 0.45 ), memories (such as CsPbBrI 2 ), lasers (such as MAPbBr 3 ), etc. − Finally, the versality of the whole method has also been tested for different substrates, especially textured substrates that are often used as the upper antireflex layer in solar cells. , We initially tried to conformally deposit a layer of the perovskite film on a textured crystalline silicon cell by the electrochemical strategy, which illustrates the versatility of the strategy and provides a new idea for the simple preparation of two-terminal perovskite solar cells (as shown in Figure S7).…”

Efficacy of Perovskite Photocatalysis: Challenges to Overcome

“…However, one must be careful when employing scavengers to remove photogenerated electrons or holes, as recently demonstrated using TCNQ electron scavengers. 171 Although added TCNQ was able to efficiently capture electrons in the presence of a CsPbBr 3 photoelectrode, TCNQ also mediated halide exchange between the DCM solvent and the halide perovskite, leading to spectral shifts in the perovskite absorption and eventual decomposition of the perovskite film during photoirradiation. This highlights the need for careful mechanistic studies of perovskite photocatalysis under steady-state irradiation conditions, where long-term charge generation can lead to processes that would otherwise be missed in time-resolved experiments that employ pulsed laser excitation.…”

“…Charge separation, achieved by quick transfer of photogenerated electrons from the perovskite into TiO 2 , resulted in a 4-fold enhancement of photocatalytic oxidation efficiency. However, one must be careful when employing scavengers to remove photogenerated electrons or holes, as recently demonstrated using TCNQ electron scavengers . Although added TCNQ was able to efficiently capture electrons in the presence of a CsPbBr 3 photoelectrode, TCNQ also mediated halide exchange between the DCM solvent and the halide perovskite, leading to spectral shifts in the perovskite absorption and eventual decomposition of the perovskite film during photo­irradiation.…”

Molecular relays in nanometer-scale alumina: effective encapsulation for water-submersed halide perovskite photocathodes

“…The latter is most challenging due to the solubility of HaPs in water. [28][29][30][31][32] But it can also be highly rewarding due to the higher concentration of reactants (e.g., protons) and the availability of membranes and other cell components (most are stable in water but not in organic solvents), and by using a 'greener' solvent. At the same time, HaP photoelectrochemistry is an emerging research field.…”

“…At the same time, HaP photoelectrochemistry is an emerging research field. 28,29,33 Therefore, effective encapsulation methods are scientifically and technologically attractive.…”