Recently, hole-transport material (HTM)-free mesoporous perovskite solar cells (PSCs) with carbon electrodes have attracted great attention due to their high stability and low fabrication cost. However, the power conversion efficiency of HTM-free PSCs with carbon electrodes is not high enough due to the lack of a proper perovskite coating method. In this work, very uniform and dense perovskite films were prepared by the acid−base reaction between the dimethylammonium lead iodide (DMAPbI 3 , so-called HPbI 3 ) solid and the methylamine (CH 3 NH 2 ) gas. The results showed that the contact between the perovskite layer and the porous carbon layer was improved by increasing the concentration of the DMAPbI 3 solution, possibly due to the enhancement of pore filling in the perovskite layer within the mesoporous structure and the increase of the crystal size of the perovskite layer. It was also found that the solid−gas reaction time between DMAPbI 3 and CH 3 NH 2 had a serious influence on the crystallization of the perovskite film. The fabricated HTM-free mesoporous PSCs with carbon electrodes demonstrated a high efficiency of 15.04%, together with a decrease in device hysteresis and improvement in device stability.

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