Surface coverage enhancement of a mixed halide perovskite film by using an UV-ozone treatment

Recently, a significant breakthrough in emerging photovoltaics occurred. Now, perovskite solar cells, hybrid types of organic and inorganic solar cells, are considered as reliable next-generation solar cells due to their outstanding photovoltaic performance. Records of the National Renewable Energy Laboratory (NREL) on cell efficiency research indicates a prominent growth in the power conversion efficiency (PCE) of a perovskite solar cells which is now approaching 20.1%. Perovskite solar cells are, in general, classified into three types based on their structures; the mesoporous type with TiO₂ nanoparticles, the meso-superstructure type with Al₂O₃ and the planar hetero-junction type. Among them, planar-structured perovskite solar cells have strong advantages due to their easy processibility and flexibility. We can replace the materials in the electron transport layer (ETL) and the hole transport layer (HTL) with common materials that are available in organic solar cells. However, a great challenge is to fabricate a high-quality perovskite film because the perovskite morphology is highly sensitive to its fabrication conditions. For control of the film’s morphology, some experiments, such as changing the annealing temperature or time and adding some additives, have been done to increase the surface coverage of perovskite films. In this work, we introduce normal, planar, perovskite solar cells with a hetero-junction structure based on compact TiO₂ and a mixed halide perovskite (CH₃NH₃PbI_3−xCl_x). To enlarge the surface coverage of perovskite film, we used an UV-ozone treatment on top of the compact TiO₂, which made the surface of TiO₂ hydrophilic. Because a perovskite precursor is hydrophilic, an UV-ozone treatment is expected to improve the wettability between the compact TiO₂ and the perovskite film. Here, we present the photovoltaic performance, along with the surface coverage difference, for various UV-ozone treatment time. In addition, the effect of the UV-ozone treatment was examined by using an opto-electronic analysis.