Preparation And Properties Of Lead-free Perovskite Films And Solar Cells

This dissertation begins with how to prepare new perovskite solar cells that are lead-free,low-toxic and stable.The effects of reducing molecules on the performance of tin-based perovskite cells were also studied.The effect of bromine-doped cerium-based calcium-titanium solar cells on their cell efficiency was also studied.The main conclusions are as follows:The environmentally friendly additive 2,2,2-trifluoroethylamine hydrochloride?TFEACl?is used in synergy with SnF₂ to enhance the efficiency and stability of FASnI₃based solar cells.Both TFEACl and Cl^-are present in the films,but only Cl^-is incorporated into the crystal lattice of the perovskite.The addition of TFEACl suppresses the segregation of SnF₂,resulting in improvements infilm morphology,in addition to a more favorable energy band alignment,andimproved suppression of the formation of Sn4⁺.Consequently,reducedcharge recombination and improved charge collection result in an efficiency enhancement from 3.63to 5.30%.The stability of the devices is alsosignificantly enhanced,with devices with TFEACl retaining over 60%of initial PCE after 350 h of light soaking in ambient,while devices without TFEACl experience failure in 120 h under the same testing condition.Then we have realized the bandgap engineering of Cs₃Bi₂I_9-xBr_x perovskite materials with alloying Br into Cs₃Bi₂I₉.Through a series of Br/I ratio sorting,we discovered a unique phenomenon that Cs₃Bi₂I₆Br₃ shows the lowest bandgap of 2.03 eV,while that of Cs₃Bi₂I₉ is2.20 eV,because the alloying of Br ions often results in larger bandgap in principle due to smaller ionic size and smaller lattice distance.In this paper,their electronic structures were clearly revealed and proved by both photophysical characterizations and DFT calculations.Moreover,the composition engineering also leads to compact Cs₃Bi₂I₆Br₃ films with high crystalline and orientation,which results in a champion device with the PCE of 1.15%.With the increased Br/I ratio,the phase transition from P6₃/mmc to P3?m was discovered and accounts for the bandgap shrinking and better optoelectronic properties for devices.