Analysis of substrate coverage of hybrid halide perovskite thin films deposited on planar surfaces

J. CARAM; N. BUDINI; R. D. ARCE

Gramado

Encuentro; XVI SBPMat; 2017

Since 2009 a new generation of solar cells has emerged. These new devices arebased on the Grätzel solar cells, being the active layer the hybrid organo-metalic perovskite. The efficiency of the perovskite cells has grown in a surprising way, reaching values close to 22% in a few years. The possibility of using the wet route for the synthesis of the different layers leads to a significant fall in manufacturing costs, transforming these devices into competitive alternatives compared to those developed by traditional technologies. The development of optoelectronic devices in the form of sandwich requires the control of the homogeneity and continuity of the films prepared, essentially a high coverage of the surface must be achieved. A high degree of coverage, defined as the ratio between the total area and the covered area, avoids the presence of pin holes that shorten the different layers of the cell. The devices prepared from a solution of PbI2/CH3NH3I or PbCl2/CH3NH3I, using gamma-butyrolactone or dimethylformamide as solvents are so far the ones that show the best results. The solutions containing the precursors are deposited as thin films by spin-coating or dip-coating, and then annealed at 85 °C in a N2 environment. The crystallization process of these perovskites is extremely fast, giving rise to nucleation centers that agglutinate the film in regions of the substrate, generating the possibility of pin-holes formation. On the other hand, the phenomena of charge transport are still under discussion. In order to study these processes it is necessary to dominate the synthesis of thin films on planar interfaces making possible direct conductivity and photoconductivity measurements. This work presents an analysis of the synthesis methods, on several kinds of substrates. We found remarkable improvements in the coverage percentage when using specific chemical treatments on the substrate as well as the addition of solvents during the synthesis.