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Black-phase formamidinium lead iodide (FAPbI3), with a narrow bandgap and high thermal stability, has emerged as an in-demand material for highly efficient perovskite solar cells (PSCs). In a two-step sequential deposition, the PbI2 film plays an important role in the formation of a perovskite film with desirable qualities. This paper explores using N-methyl-2-pyrrolidone (NMP), a strong Lewis base, and N,N-dimethylformamide (DMF) as a mixed precursor solvent (DMF/NMP) of PbI2 and reports on preparing PbI2 films with a porous morphology by thermal treatment. Porous PbI2 films ensure the diffusion and sufficient reaction of the formamidinium iodide solution to form a smooth perovskite film. In addition, a dynamic spin coating method is also introduced to improve the uniformity of the perovskite film. Both methods yield a pure α-phase FAPbI3 film immediately in the unannealed state, which is necessary for the perovskite film to maintain phase stability. Finally, PSCs with a power conversion efficiency of 21.20% (0.13 cm2) are fabricated and optimized. The unencapsulated PSCs retain 90% of the initial efficiency for 1000 hours in dry air and exhibit a good thermal stability when heated to 85 °C. [ABSTRACT FROM AUTHOR]

Sodium sulfate accumulation in the water system is a common problem in the production of primary metals from sulfide minerals. In flash smelting-flash converting copper smelters, when molten copper matte quenched in industrial water to produce matte granules, Na2SO4 precipitated and entered the system, which had negative influence on the matte converting process. The reaction behaviors of copper matte powder containing Na2SO4 have been studied through thermodynamic calculation and single-particle experiments. Calculated results showed that a liquid sulfate phase, Na2S containing copper matte, and Cu–Na alloy may form in the processing conditions of the converting process. The influence of the Na2SO4 dosage, fluxing conditions, and processing temperature has been systematically studied, and the results obtained showed that: (1); Na2SO4 physically precipitated on matte particles, and the Cu–Na alloy phase was found within copper phase in reacted particles; (2); Na2SO4 contamination hindered oxygen transfer by forming a low melting sulfate phase, and the de-sulfuration rate of matte powder changed dramatically along with the variation in Na2SO4 amount; (3); CaO flux was able to promote the converting reactions and Na2SO4 transformation; (4); Na2SO4 melt and formed a sulphate layer on matte particles at 1000 °C, Cu–Na alloy phase was found in samples collected at 1200 °C, and Cu–Na–O phase was detected in blister copper at 1600 °C. [ABSTRACT FROM AUTHOR]

Black-phase formamidinium lead iodide (FAPbI 3 ), with a narrow bandgap and high thermal stability, has emerged as an in-demand material for highly efficient perovskite solar cells (PSCs). In a two-step sequential deposition, the PbI 2 film plays an important role in the formation of a perovskite film with desirable qualities. This paper explores using N-methyl-2-pyrrolidone (NMP), a strong Lewis base, and N,N-dimethylformamide (DMF) as a mixed precursor solvent (DMF/NMP) of PbI 2 and reports on preparing PbI 2 films with a porous morphology by thermal treatment. Porous PbI 2 films ensure the diffusion and sufficient reaction of the formamidinium iodide solution to form a smooth perovskite film. In addition, a dynamic spin coating method is also introduced to improve the uniformity of the perovskite film. Both methods yield a pure α-phase FAPbI 3 film immediately in the unannealed state, which is necessary for the perovskite film to maintain phase stability. Finally, PSCs with a power conversion efficiency of 21.20% (0.13 cm 2 ) are fabricated and optimized. The unencapsulated PSCs retain 90% of the initial efficiency for 1000 hours in dry air and exhibit a good thermal stability when heated to 85 °C.