Research On Highly Efficient And Stable Perovskite Solar Cells Fabricated In Air

The metal halide perovskite is a kind of semiconductor with tunable bandgap,long carrier diffusion length,bipolar transmission and low fabrication cost.The metal halide perovskites are widely used in the fields of light-emitting diodes,X-ray detectors and solar cells.At present,most of the reported highly efficient perovskite solar cells were prepared in glove box with inert gas,which elevates the costs and hinders the large-scale manufacture of devices.The organic-inorganic hybrid FAMAPbI₃ and all-inorganic CsPbI₂Br are two typical perovskites semiconductors.The method to fabricate FAMAPbI₃ and CsPbI₂Br films with low trap density is one of the research focuses of perovskite solar cells.In this study,the high-quality FAMAPbI₃ and CsPbI₂Br films and corresponding solar cells were fabricated in dry air by regulating the nucleation-crystallization process of perovskites.The relationships between the photovoltaic performance,composition and crystal structure of these two perovskites were investigated.In detail,the work have carried out the following investigations.First of all,the relationship between growth of FAMAPbI₃ crystal and the morphology of substrate were systematically studied.The FAMAPbI₃ thin film with grain size>1?m was prepared by reducing the roughness of the substrate as well as the heterogeneous nucleation.The results indicate that the FAMAPbI₃ film grown on the island-like nano-TiO₂ substrate shows higher electron-extraction efficiency and lower grain boundary density,which effectively suppresses carrier recombination and improves the open circuit voltage and efficiency of the devices.Finally,the device based on island-like nano-TiO₂ substrates achieved an efficiency of 23.12%.However,the efficiency of FAMAPbI₃ device dropped fast under continuous light illumination in ambient atmosphere,which is unstable for practical applications.Secondly,this study used a preheating method to prepare high-quality all-inorganic CsPbI₂Br films.The preheating method led to the formation of bromine-rich CsPbI_2-XBr_1+X perovskite seed crystals in the wet film.The seed crystal-assisted perovskite growth has some advantages including less grain boundaries,strong light absorption and low defect density.In addition,the oxygen atoms introduced in the preparation process can effectively passivate halogen vacancies,which is beneficial for the suppression of non-radiative recombination in the CsPbI₂Br film.Therefore,the CsPbI₂Br solar cell prepared by preheating method achieved an efficiency>14%and an open circuit voltage>1.30 V.Further investigation indicated the gradient energy level structure in the CsPbI₂Br film prepared by the preheating method,which helps to reduce the energy level mismatch between the perovskite and the carrier transporting layers.In addition,the efficiency of the CsPbI_xBr_3-X solar cell was further increased to15.29%with an open circuit voltage of 1.359 V by optimizing the I/Br ratio in perovskites.Moreover,an efficiency of 11.26%was also achieved with an active area of 1 cm².On the other hand,in order to improve the interfacial contact and energy level mismatch between the carbon electrode and the CsPbI₂Br film,a carbon black interlayer was introduced.Due to the more suitable energy band alignment and the improved interfacial contact between the carbon black intelayer and the CsPbI₂Br film,the extraction of holes was facilitated.The experiments results indicated that the device based on the 4?m carbon black interlayer achieved the best efficiency of 12.41%.Moreover,carbon black nanoparticle diffusion happened during the heating or storage.The diffusion leads to the formation of carbon black-CsPbI₂Br bulk heterojunction and the enhancement of device efficiency.As a result,the champion efficiency of 13.13%was achieved on the device heated at 85?for 562 hours,which is also the highest efficiency of CsPbI₂Br solar cells based on carbon electrode.In summary,this work has fabricated high-quality FAMAPbI₃ and CsPbI₂Br perovskite films in dry air by regulating the nucleation-crystallization process.Devices based on these films achieved high photovoltaic performance.Furthermore,the efficiency of CsPbI₂Br solar cells based on carbon electrode was further improved by optimizing interfacial contact and energy level matching.Moreover,the oxygen helps to reduce non-radiative recombination and improve the performance of devices,Therefore,it is feasible to prepare high-performance FAMAPbI₃ and CsPbI₂Br solar cells in dry air.