Study On The Perovskite Solar Cells Based On Highly-porous Mesoporous Layer And Lead-free Perovskite

Perovskite solar cells based on CH₃NH₃PbI₃ have attracted much attention.It has been reported that the structural properties of the mp-TiO₂ layer,such as particle size,thickness and porosity,have a significant influence on the performance of PSCs.Highly porous mp-TiO₂ films promote the easy infiltration of perovskite which subsequently fills the pores.A higher deposition of perovskites in mp-TiO₂ film results in increased light absorption and a higher current density.Moreover,the interface between the mp-TiO₂ film and perovskite film plays a key role in determining the overall conversion efficiency of PSCs.Increasing the specific surface area and porosity of mp-TiO₂ film can promote a deeper infiltration of perovskites in TiO₂ films.This superior infiltration is thought as an effective way to decrease the contact barrier between the TiO₂/MAPbI3 interfaces,which could improve the transport of carriers in the solar cell.In this study,we fabricated highly porous mp-TiO₂ films by doping polystyrene spheres in TiO₂ paste.The crystallinity and composition of the perovskite films were effectively improved by modifying the mass fraction of the PS spheres in the TiO₂ paste.Due to the high porosity of the mp-Ti O₂ film,PbI——2 and CH₃NH-3 I could sufficiently infiltrate into the network of the mp-TiO₂ film,which ensured a more complete transformation to MAPbI3.The surface morphology of the mp-TiO₂ film and the photoelectric performance of the perovskite solar cells were investigated.The results showed that an increase in the porosity of the mp-TiO₂ film resulted in an improvement in the performance of the PSCs.The best device with the optimized mass fraction of 1.0 wt% PS in Ti O₂ paste exhibited an efficiency of 12.69%,which is 25% higher than the efficiency of the PSCs without PS spheres.One major disadvantage with the MAPbX₃ perovskite is that it contains lead?Pb?,which is rather toxic.An important task is therefore to replace lead in the perovskite,with a different less toxic element.Among other perovskite materials without lead photovoltaic properties,MA₃Bi₂I₉ perovskite has caused the attention of researchers.Nowadays the preparation of MA₃Bi₂I₉ perovskite usually used one-step solution method.Perovskite prepared by this method has a big grain size and high surface roughness.The MA₃Bi₂I₉ perovskite films with large grain size,low surface roughness and high surface coverage were obtained by low-pressure vapor-assisted solution process?LP-VASP?.The photoelectric conversion efficiency of 0.107% was obtained.In order to further optimize the performance of the MA₃Bi₂I₉ perovskite solar cell,the solvent of Bi I₃ was changed and the effect of the plate structure and mesoporous structure on the cell performance was investigated.The results showed that the BiI₃ film with DMF as the solvent had good flatness and the MA₃Bi₂I₉ perovskite particles were homogeneous and had high coverage.After removal of the mesoporous layer,the short-circuit current of the solar cell was significantly improved,from 0.48 mA to 0.55 mA,the cell efficiency increased by 50%.In order to improve the short-circuit current of the solar cell,FAI and MAI was mixed to prepare MA_x FA_1-xBi₂I₉ perovskite,which reduced the perovskite band gap and increased the absorption of perovskite in long-wave band.The photoelectric efficiency of 0.170% was obtained.