High temperature stable inorganic CsPbX 3 (X: I, Br, or mixed halides) perovskites with their bandgap tailored by tuning the halide composition offer promising opportunities in the design of ideal top cells for high-efficiency tandem solar cells. Unfortunately, the current high-efficiency CsPbX 3 perovskite solar cells (PSCs) are prepared in vacuum, a moisture-free glovebox or other low-humidity conditions due to their poor moisture stability. Herein, a new precursor system (HCOOCs, HPbI 3 , and HPbBr 3 ) is developed to replace the traditional precursors (CsI, PbI 2 , and PbBr 2 ) commonly used for solar cells of this type. Both the experiments and calculations reveal that a new complex (HCOOH•Cs + ) is generated in this precursor system. The new complex is not only stable against aging in humid air ambient at 91% relative humidity, but also effectively slows the perovskite crystallization, making it possible to eliminate the popular antisolvent used in the perovskite CsPbI 2 Br film deposition. The CsPbI 2 Br PSCs based on the new precursor system achieve a champion efficiency of 16.14%, the highest for inorganic PSCs prepared in ambient air conditions. Meanwhile, high air stability is demonstrated for an unencapsulated CsPbI 2 Br PSC with 92% of the original efficiency remaining after more than 800 h aging in ambient air.
The processing solvents strongly impact the crystallization and optoelectronic properties of the resultant perovskites. However, limited by the solubility of perovskites, available processing solvents for perovskite light-emitting diodes (PeLEDs) are restricted to only a few strongly coordinated and polar solvents, such as dimethyl sulfoxide (DMSO). The strong coordination capability of DMSO with Pb 2+ excessively affects the crystallization of perovskites, often necessitating anti-solvent engineering to regulate the crystallization process. Here, a strategy of weakly coordinated co-solvent comprising 2-methoxyethanol (2-ME) and propylene carbonate (PC) is proposed to fabricate quasi-2Dperovskites and PeLEDs. This co-solvent exhibits synergistic properties—complementary coordination capability and dielectric constant—yielding superior solvation capability compared to either solvent alone. Crucially, the tunable, moderate solvation strength of the 2-ME:PC mixture facilitates perovskites crystallization while suppressing detrimental low-dimensional phase growth, enabling anti-solvent-free fabrication of high-quality formamidinium-based quasi-2D perovskites. Employing this optimized co-solvent, pure green PeLEDs are achieved that comply with Rec. 2020 standards, boasting a remarkable external quantum efficiency of 26.2%. This work presents an effective strategy for the facile fabrication of high-performance PeLEDs, while also guiding the selection of additional perovskite processing solvents.
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