The solvent-engineered one-step spin-coating method has been widely used to produce full-coverage CH3NH3PbI3 films for perovskite solar cells by forming an intermediate phase. However, the resultant CH3NH3PbI3 films usually contain numerous structural and compositional defects mainly resulting from the fast crystallization of the intermediate phase as well as the escape of CH3NH3I species induced by the inevitably thermal annealing recipe. Herein, a facile room-temperature intermolecular exchange route is proposed to enable conversion of the intermediate phase into uniform and ultra-flat CH3NH3PbI3 films. It can effectively inhibit the formation of structural and compositional defects in the resultant films, and even repair their inherent defects. As a result, the efficiency of perovskite solar cells can be boosted to 19.45% with a stabilized value of 18.55%, which is much higher than that from the ones fabricated by thermal annealing. This study suggests a facile and low-cost route to room-temperature fabrication of highly efficient perovskite solar cells including flexible ones.
Keywords: CH3NH3PbI3; defects; intermediate phase; intermolecular exchange; perovskite solar cells; room temperature.