Effects of anti-solvent (iodobenzene) volume on the formation of CH ₃ NH ₃ PbI ₃ thin films and their application in photovoltaic cells

An antisolvent (iodobenzene, IB) was used to assist the formation of closely packed CH ₃ NH ₃ PbI ₃ (MAPbI ₃ ) thin films during the one-step spin-coating process using different volumes of IB. The morphological, structural, optical and excitonic properties of MAPbI ₃ thin films were analyzed using a contact-mode atomic-force microscope, X-ray diffractometer, broadband absorbance spectrometer and optical microscope-based time-resolved photoluminescence spectrometer. The properties of the resultant MAPbI ₃ thin films can be manipulated by using different IB volumes, which dominates the device performance of MAPbI ₃ based photovoltaic cells. The experimental results show that the grain size (or particle size) of MAPbI ₃ thin films influences the collection of photoexcited carriers and the contact at the 6,6-Phenyl C ₆₁ butyric acid methyl ester (PCBM)/MAPbI ₃ interface, thereby resulting in a trade-off between the fill factor (FF) and short-circuit current density (J _SC ). In addition, it is predicted that the power conversion efficiency (PCE) can be further improved by increasing the crystallinity of the MAPbI ₃ thin film while keeping the small grain size.