Understanding the Effect of Delay Time of Solvent Washing on the Performances of Perovskite Solar Cells

Uniform and dense perovskite films were realized by the one-step solution-processing method combined with toluene washing. The influence of the delay time applied for toluene washing on the film quality of CH 3 NH 3 PbI 3 (MAPbI 3 ) was investigated in a comprehensive manner. The optimal delay time was experimentally observed at the critical point when the color of the film changes from transparent to hazy. A detailed X-ray diffraction study suggested that such a color change was caused by the emergence of the MAPbI 3 crystal nucleus. This finding provides a convenient method to determine the optimal time accurately. With the optimal delay time, the most uniformly distributed MAPbI 3 grains with the largest average grain size and the smoothest surface were obtained. Owing to the realization of homogeneous MAPbI 3 films combined with full coverage of perovskite on the substrate achieved by toluene washing at the critical point, open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of 1.11 V, 18.24 mA/cm 2 , 77.47, and 15.54% were obtained.