Organic–inorganic hybrid halide perovskites are proven to be a promising semiconductor material as the absorber layer of solar cells. However, the perovskite films always suffer from nonuniform coverage or high trap state density due to the polycrystalline characteristics, which degrade the photoelectric properties of thin films. Herein, the alkali metal ions which are stable against oxidation and reduction are used in the perovskite precursor solution to induce the process of crystallization and nucleation, then affect the properties of the perovskite film. It is found that the addition of the alkali metal ions clearly improves the quality of perovskite film: enlarges the grain sizes, reduces the defect state density, passivates the grain boundaries, increases the built‐in potential (V bi), resulting to the enhancement in the power conversion efficiency of perovskite thin film solar cell.

Electron transport layer (ETL), facilitating charge carrier separation and electron extraction, is a key component in planar perovskite solar cells (PSCs). We developed an effective ETL using low-temperature solution-processed Nb-doped SnO (Nb:SnO). Compared to the pristine SnO, the power conversion efficiency of PSCs based on Nb:SnO ETL is raised to 17.57% from 15.13%. The splendid performance is attributed to the excellent optical and electronic properties of the Nb:SnO material, such as smooth surface, high electron mobility, appropriate electrical conductivity, therefore making a better growth platform for a high quality perovskite absorber layer. Experimental analyses reveal that the Nb:SnO ETL significantly enhances the electron extraction and effectively suppresses charge recombination, leading to improved solar cell performance.

Homogeneous molecular precursor solutions are excellent choices for obtaining smooth absorber layers, and they offer the potential to significantly lower the manufacturing cost of solar cells. Here, we present a thermally degradable metal butyldithiocarbamate-based solution approach to fabricate Cu2ZnSn(S,Se)4 solar cells. Low-cost Cu2O, ZnO, and SnO were used as the starting materials and were dissolved in the ethanol solution of butyldithiocarbamic acid. By tuning the composition of the Cu2ZnSn(S,Se)4 thin film, a power conversion efficiency of 6.03% on the basis of the active area has been achieved.

We developed a versatile and environmentally friendly solution approach for the fabrication of a variety of metal sulfide nanocrystal thin films. Metal oxides, metal hydroxides, metal chlorides, metal acetates, and metal acetylacetonates can be used as the starting materials and dissolved in thioglycolic acid and ethanolamine, forming many types of metal–organic precursor solutions. High quality CdS, SnS, CuInS2, CuSbS2, Cu2ZnSnS4, Cu­(In0.7Ga0.3)­S2, and luminescent Ag-doped Zn x Cd1–x S nanocrystal thin films have been successfully prepared by spin-coating their corresponding metal precursor solutions. Cu2ZnSn­(S,Se)4 thin film solar cell with a power conversion efficiency of 6.83% has been realized by this versatile method.