In this paper, a two-step method is used to prepare a high-quality CH 3 NH 3 PbI 3 layer for carbon-based hole conductor-free perovskite solar cells (PSCs). In the first step, the solvent for the PbI 2 /DMF solution is changed to a mixed solvent of N,N -dimethylformamide (DMF) with dimethyl sulfoxide (DMSO) from pure DMF solvent. This process requires 3.5 h for PbI 2 films deposited from the PbI 2 /DMF solution to completely convert to perovskite in a methyl amine iodide (MAI)/iso-propyl alcohol (IPA) solution, and perovskite films have a rough surface with a few large crystals. This mixed solvent accelerates the conversion of PbI 2 to CH 3 NH 3 PbI 3 , resulting in smooth CH 3 NH 3 PbI 3 films without residual PbI 2 . Only 15 min are required for PbI 2 films to completely convert to perovskite when the volume ratio of DMSO to DMF is 1:4. As a result, the photovoltaic performance, especially on the fill factor (FF) of PSCs fabricated from DMF/DMSO solvent, improved mainly due to the better contact of perovskite/carbon interface and faster charge transport of the perovskite layer.
Bo Zhou,Dong Ding,Ye Wang,Shaofan Fang,Zexiang Liu,Jian Tang,Henan Li,Haizhe Zhong,Bingbing Tian,Yumeng Shi
All-inorganic cesium lead bromide perovskites have attracted a lot of attention because of their excellent optical properties that can potentially be applied in various optical devices. However, large-scale preparation of cesium lead bromide perovskites with outstanding optical performance is still hindered by the poor solubility of CsBr in polar aprotic solvents. In this work, a water/dimethylsulfoxide (DMSO)/dimethylformamide (DMF) system is demonstrated for the synthesis of inorganic cesium lead bromide perovskites, where the introduction of water can effectively address the dissolution issue of Cs + ions. Large-scale synthesis of pure-phase emissive Cs 4 PbBr 6 with a product yield of up to 73% is achieved and the photoluminescence quantum yield of resulting product reaches as high as 76%. The origin of the light emission is further revealed by the photoluminescence evolution of the colored Cs 4 PbBr 6 single crystals. Furthermore, reversible phase transitions between Cs 4 PbBr 6 , CsPbBr 3 and CsPb 2 Br 5 are achieved by changing solely the water content, which paves the way for the recycle of the mother solution of Cs 4 PbBr 6 without generation of additional hazardous waste. The three-solvent-based synthetic approaches enable an economical, robust, and large-scale production for all-inorganic cesium lead bromide perovskites.
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