Control of the Morphology and Crystallinity of a PbI2 Layer for Large-Area Perovskite Films Prepared by Close Space Sublimation

In this work, homogeneous PbI2 films were prepared by the spin-coating technique from PbI2-DMF solutions heated at temperatures ranging from room temperature to 120 degrees C. The homogeneity and morphology of the films change according to the used temperature of solution and are related to the size and distribution of PbI2 grains; the best crystallinity was observed when PbI2 solution was preheated at 100 degrees C. Lead halide perovskite films were prepared by close space sublimation of CH3NH3I over the prepared PbI2 films, and the area of the deposited films was 5 cm(2). The transformation of PbI2 into perovskite was carried out at 100 degrees C under a pressure of 0.8 bar. A remarkable issue reported here is that, by controlling the morphology of the PbI2 layer with the temperature of PbI2-DMF solutions, the final features of MAPbI(3) films can be controlled without requiring extra treatment. Therefore, the device with the best performance, out of a set fabricated with architecture ITO/PEDOT:PSS/perovskite/PC71BM/cathode, corresponded to the PbI2 film deposited at 100 degrees C. This device reached an efficiency of 8.7%. As a cathode, an eutectic alloy of Bi:In:Sn with a melting point of 65 degrees C was easily deposited without the use of high vacuum. Thus, this work describes a practical way to fabricate perovskite solar cells with efficiencies up to 8.7%.