Suppressing Halide Phase Segregation in CsPbIBr₂ Films by Polymer Modification for Hysteresis-Less All-Inorganic Perovskite Solar Cells

Abstract

All-inorganic perovskite CsPbIBr2 materials are promising for optoelectronics, owing to their upgraded ambient stability and suitable bandgap. Unfortunately, they generally undergo severe halide phase segregation under illumination, which creates many iodide-rich and bromide-rich domains coupled with significant deterioration of their optical/electrical properties. Herein, we propose a facile and effective strategy to overcome the halide phase segregation in the CsPbIBr2 film by modifying its crystalline grains with poly­(methyl methacrylate) (PMMA) for the first time. Such a strategy is proceeded by covering a PMMA layer on the substrate before deposition of the CsPbIBr2 film. Further investigations manifest that the CsPbIBr2 film with PMMA possesses larger grains, better crystallinity, and fewer traps than the one without any modification. Moreover, it holds the nearly eliminated halide phase segregation. Therefore, the carbon-based, all-inorganic CsPbIBr2 perovskite solar cell exhibits the much suppressed photocurrent hysteresis, coupled with an outstanding efficiency of 9.21% and a high photovoltage of 1.307 V.

Quantum Dot Passivation of Halide Perovskite Films with Reduced Defects, Suppressed Phase Segregation, and Enhanced Stability

“…The suppressed phase segregation can be attributed to the reduced surface defects and immobile ions due to the passivation effect of the QD treatment. [ 66–70 ]…”

“…The suppressed phase segregation can be attributed to the reduced surface defects and immobile ions due to the passivation effect of the QD treatment. [66][67][68][69][70] To further understand the effect of CsPbBr 3 QD treatment on CsPbIBr 2 films, DFT calculations were carried out with a focus on the passivation of under-charged Pb 2+ and halide vacancies with carboxyl (-COOH) groups. The details of the employed computational method are described in the Experimental Section.…”

Efficient and Stable All‐Inorganic CsPbIBr2 Perovskite Solar Cells Enabled by Dynamic Vacuum‐Assisted Low‐Temperature Engineering

“…However, the average CSP of VALT‐CsPbIBr 2 film is nearly reduced by ≈0.30 V versus that of HT‐CsPbIBr 2 film, which indicates the larger work function of VALT‐CsPbIBr 2 film. [ 39 ] Generally, the enhanced work function of VALT‐CsPbIBr 2 film is ascribed to its fewer compositional defects caused by its weaker n‐type doping, which is corroborated by the preferable stoichiometric ratios of VALT‐CsPbIBr 2 film versus that of HT‐CsPbIBr 2 obtained from the X‐ray photoelectron spectroscopy (XPS) result (Figure S4, Supporting Information). The larger work function of VALT‐CsPbIBr 2 film is not only beneficial for improving the structural stability of VALT‐CsPbIBr 2 but also profitable to obtain a larger built‐in potential for derived devices.…”

A Thermal‐Pressed Strategy for Crystal Growth and Boundaries Self‐Fusion of Mixed‐Halide Perovskite Films against Halide Phase Segregation

“…[24,25] The I-rich regions can act as traps and recombination centers to compromise the carrier extraction efficiency and the open-circuit voltage (V oc ) of photovoltaic device. [19,26,27] Therefore, halide phase segregation makes CsPbI 3−x Br x materials to deviate their inherent properties and deteriorate their photoelectrical performance as well, hindering critical developments of them in future.Several models have been adopted to illustrate the halide segregation mechanism, including polaron-induced lattice strain, [24,28] two-state model, [10] and halide vacancy formation. [18,25,29] However, detailed understanding of it is still challenging due to the complex interaction between thermodynamics and kinetics in the movement of halide ions.…”

“…[24,25] The I-rich regions can act as traps and recombination centers to compromise the carrier extraction efficiency and the open-circuit voltage (V oc ) of photovoltaic device. [19,26,27] Therefore, halide phase segregation makes CsPbI 3−x Br x materials to deviate their inherent properties and deteriorate their photoelectrical performance as well, hindering critical developments of them in future.…”