Systematic Study Of The Role Of Compact Layer In The Organometal Halide Perovskite-based Solar Cells

The dye-sensitized solar cell (DSSC), invented by Michael Gra’tzel and Brian O’Regan in1991, has been an attractive alternative to existing β-n junction solar cells, shown great promise for using in the converting of solar energy into electrical power. What’s more noteworthy is that, the development of perovskite-based solar cell, whose power conversion efficiency has skyrocketed to nearly20%since its first report, in no more than10years. And by virtue of its simple device fabricated procedure, this kind of cell obtains both less cost and less pollution, compared to the traditional dye, like N3, N719etc. Furthermore, not only can the perovskite materials act as the dye, it also can transport the electron and the hole, which means that both the TiO2nanoparticle used as the electron transporting and the hole transporting material can be omitted. For this reason, the simplification of device structure of lead halide perovskite-based solar cell has been an hot research field recently. Due to all those advantages, perovskite-based solar cell is considered as the new hope of photovoltaic area.As we already known that the key factor of low efficiency of dye sensitized solar cell is the recombination of photo-generated electron, instead of transporting to the FTO, the electron recombine with the oxidized HTM molecular or oxidized dye molecular, lead to a low current export. The add of TiO2compact layer (CL) will effectively suppress the recombination. Though the study of TiO2-CL on the liquid-or solid-state dye sensitized solar cell has been well reported, no relative study of the influence of compact layer on the perovskite-based solar cell has been published, so we made the systemic investigation of the influence of compact layer on the perovskite-based solar cell. Coming to the following4conclusions:1. We made different compact layers with different conductivity and density by the dipping method(DIP) and Physical Vapor Deposition method(PVD). Then we applied them to the perovskite-based solar cells with different HTMS(P3HT and spiro-OMeTAD). Since the size and conductivity of these two HTMs are different, there must exist different requirement for compact layers. We found that when the utilized HTM was Spior-OMeTAD, whose molecular size is smaller and conductivity is lower, the compact layer made by PVD showed better performance.2. Furthermore, we made compact layer with different thicknesses through the spray pyrolysis deposition, which is a more cheaper and controllable method. After studying the influence of compact layer thickness on the perovskite-based solar cell, we came to the conclusion that～90nm CL will be the optimum thickness for perovskite-based solar cell by showing the best cell performance and the highest hole-electron recombination retardation.3. It reported that there existed two possible electron transport paths in the perovskite-based solar cell, namely transporting through the TiO2nanoparticles and through perovskite itself. We made3kinds of solar cells with different device structures, and the third one obtained only one path for electron transporting. Our result suggested that the nc-TiO2was important in the electron transporting in perovskite-based solar cell, offering an evidence of electron transport massage from the aspect of compact layer;4. Knowing that the nc-TiO2is important to the electron transport in perovskite-based solar cell, we also found that there existed a gap between the TiO2compact layer and TiO2nanoparticle, which will hinder the electron transporting from nc-TiO2to the CL. In order to eliminate this gap, we used isolated metal oxide to modify the TiO2compact layer to give a hybridized MO-TiO2CL. That was fabricated by immersing the FTO/TiO2CL into metal salt solution for a short period of time (about several minutes) at75℃, then dried at air condition. Without any further modification, the diluted TiO2paste was spin-coated on it, and then heated at500℃for30min. During this period, the metal salt dehydrated, and the dehydration process eliminated the gap between nc-TiO2and CL. This method effectively improved the electron transportation from nc-TiO2to FTO glass, resulting to a current density enhancement. Finally, the efficiency of perovskite based solar cells increased by67%in our work.