Formation of perovskite by solid-gas reaction through low-temperature carbon counter electrode in hole-conductor-free perovskite solar cells

Recently, hole-conductor-free perovskite solar cells (PSCs) with carbon counter electrode (CCE) have attracted great attention for its high stability and low fabrication cost. Furthermore, it would lower the cost and simplify the manufacturing process of PSCs by low temperature processing instead of high temperature sintering for fabrication. In this case, however, it is very important to improve the interfacial contact between perovskite layer and CCE. In this work, we for the first time introduce solid-gas reaction between dimethylammonium lead iodide (DMAPbI 3 ) in solid state under carbon layer and methylamine (MA) gas passed through CCE which is formed at low temperature of 120 ℃. Based on Brunauer-Emmett-Teller (BET) measurement and XRD analysis , it is found that MA gas can pass through our low-temperature CCE and perovskite crystals could be successfully formed by the reaction with DMAPbI 3 . In this case, due to the existence of liquid crystal intermediate state and volume expansion, interfacial contact would become better and the charge transfer and recombination characteristics have improved considerably. The best performance devices based on optimized MA gas treatment time exhibit higher efficiency of 12.4% than that of PSCs fabricated by conventional ways with low-temperature processed CCE (9.6%).