High-performance and stable perovskite solar cells prepared with a green bi-solvent method

To simplify the fabrication procedures and improve the film quality, herein we used a bi-solvent system containing water and ethylene glycol methyl ether (EGME), which is less toxic and environmentally friendly. The bi-solvent (Volume ratio: 1:1) can dissolve CsBr and improve the solubility of CsBr, decreasing rapidly the spinning times of CsBr methanol solution and streamlining immensely multistep processes into a classical two-step methodology. The results from scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns verify the formation of a compact, homogeneous, and uniform CsPbBr3 film by the bi-solvent system. Based on this bi-solvent system, the ideal parameters during the film deposition were also discovered. In addition, we notice that the CsPbBr3 film still existed in some large-size random phases, which can be deducted as the excessive CsPb2Br5 phase through XRD patterns. For further perfection, we explore the influence of CsBr methanol solution spinning times right after the modified two-step process. The subsequently-spinning CsBr can act as a surface modifier to diminish the undesired impurity, thus enhancing the film quality and the efficiency of as-constructed CsPbBr3-based perovskite solar cells (PSCs). As a result, CsPbBr3-based PSCs, prepared by spinning coating one time with a water/ EGME solution and two times with the methanol solution of CsBr, had the optimal performance. It can reach open-circuit voltage (V-OC), short circuit current density (J(SC)), fill factor (FF) of 1.44 V, 6.26 mA center dot cm(-2), 74.57%, and the ultimate photoelectric conversion efficiency (PCE) attained 6.72%.