Interplay between nucleation and crystal growth during the formation of CH₃NH₃PbI₃ thin films and their application in solar cells

A series of nonpolar antisolvents (chlorobenzene, bromobenzene, iodobenzene and toluene) were used to assist in the formation of smooth and crystalline CH₃NH₃PbI₃ thin films by a one-step spin-coating method. The structural, optical and excitonic characteristics of the resultant CH₃NH₃PI₃ thin films were analyzed using an atomic-force microscope, X-ray diffractometer, absorbance spectrum, photoluminescence (PL) spectrum, time-resolved PL and temperature-dependent PL. The properties of the CH₃NH₃PbI₃ thin films are dependent on the relative polarity and boiling point of the nonpolar antisolvents used in the washing treatment process. The interplay between nucleation (relative polarity) and crystal growth (boiling point) during the formation of CH₃NH₃PbI₃ thin films influences the short-circuit current density (J_SC) and power conversion efficiency (PCE) of the corresponding solar cells. The experimental results demonstrate that iodobenzene can be substituted for toluene as a more efficient antisolvent in the washing treatment process during the fabrication of CH₃NH₃PbI₃ thin films. In addition, it is predicted that the J_SC and PCE can be further improved by increasing the crystallinity of the CH₃NH₃PbI₃ thin film.