Vacuum Single Source Thermal Evaporation Deposition Of Lead-based Perovskite Film And Its Solar Cell Research

Lead based perovskite of equiaxed crystal structure is direct bandgap materials,with the strong ability to absorb visible light.Simultaneously,they possess relatively high electron and hole mobilities and long migration distance.with the electron mobility almost equal to hole mobility,and the small exciton binding energy.The carrier recombination in the perovskite is very small and almost completely radiative recombination.Therefore,the lead based perovskite has received extensive attention and in-depth research as one of the most promising candidate for photovoltaic application in recent years.Vacuum single source thermal evaporation is a method for the preparation of perovskite thin films in a fully vacuum state by evaporating the solid perovskite powders to generate gasous perovskite,under the vacuum environment,and deposit them on the substrate to form solid perovskite thin films.The whole process of film formation only involves physical change without chemical reactions,so that the perovskite thin films prepared from this method with high homology.This method is easy to operate and benefits to prepare high quality perovskite thin films.The lead based perovskite thin films were prepared by the vacuum single source thermal evaporation,and their microstructures were studied.The optimum paramete rs to prepare lead based perovskite thin films were obtained b y studying the surface morphology,crystallinity,elemental composition ratio and optical properties of lead based perovskite thin films.The research concludes the following parts:The effect of thermal treating temperature on the microstructures and optical properties of CH₃NH₃PbI₃ thin films was studied.The results show that,when the target materials were heated at 160? for 20 min,some of CH₃NH₃PbI₃ perovskite was decomposed to PbI2 byproducts.However,the thermal treating temperature at 140?,the dense and uniform CH₃NH₃PbI₃ thin films were formed with large grains.Their stoichiometric ratios were in accordance with that of the ideal substances,and their bandgap was 1.56 eV.The effect of thermal treating time on the microstructure and optical properties of CH₃NH₃PbI₃ thin films was studied.The results show that the CH₃NH₃PbI₃ thin films remained when heated at 160 ? for 15 minutes,and their crystallinity was remarkably improved.The thin films were more compact and the grain became larger,and in accordance with the lead based perovskite elemental stoichiometry.The bandgap was consistent with that heated at 140? for 20 minutes.The effect of solvent assisted heat treatment on the microstructure and optical properties of C H₃NH₃PbI₃ thin films was studied.The 1,4-butyrolactone solvent was used to treat the as-deposited CH₃NH₃PbI₃ thin films at 150? for 20 minutes.The results show that after the treatment,the crystal grains of the thin films became larger,and more uniform.And the denser and flat thin films were formed with higher coverage,and the apparent surface mirror effect was observed.Their bandgap of the thin films is 1.56 eV,which is close to the theoretical bandgap.And their stoichiometric ratio is 1:3.07 which is consistent with the ideal stoichiometric ratio of 1:3.CH₃NH₃Pb₁-XSnXI₃ thin films were prepared by doping Sn into CH₃NH₃PbI₃ to study the Sn replacement effect on the properties of composites thin films.The results indicated that with the increase of Sn content,the stability of CH₃NH₃Pb₁-XSnXI₃ thin films is reduced because Sn2 + is easily oxidized to Sn4 +.When 34% Pb was replaced by Sn in the perovskite films,the CH3NH3Pb0.66Sn0.34I3 thin film reached the best properties in all samples.It was dense,flat,and uniform.Its bandgap is 1.49 e V,which is a bit less than that of CH₃NH₃PbI₃ thin film which can benefit the absorption of visible light.HC?NH₂?₂PbI₃ thin films were prepared by vacuum single source thermal evaporation and the time effect of thermal treatment time on their microstructure and properties were studied.The results show that the stability of HC?NH₂?₂PbI₃ thin films was lower than that of C H3NH3PbI3 thin films,and HC?NH₂?₂PbI₃ was more likely to decompose to PbI2 in the atmosphere.Two phases?? phase and ? phase?were formed in the atmosphere.They interacted with each other at a certain temperature.HC?NH₂?₂PbI₃ thin films prepared at 150? for 20 minutes were found without any PbI2 byproduct.Their stoichiometric ratio was in accordance with the stoichiometric ratio of the ideal substance,and the bandgap of HC?NH₂?₂PbI₃ film after thermal treatment was 1.46 eV,which was significantly smaller than that of 1.50 eV before thermal treatment.The optimized C H3NH3PbI3 perovskite thin film solar cells and the HC?NH₂?₂PbI₃ perovskite thin film solar cells were prepared by vacuum single source thermal evaporation.The results show that the lead based perovskite thin film solar cells prepared by vacuum single source thermal evaporation have obvious photoelectric response.The C H₃NH₃PbI₃ lead based perovskite thin film solar cells showed the photovoltaic performance with the short circuit current density?Jsc?of 15.36 mA/cm2,open circuit voltage?Voc?of 0.90 V,filling factor?FF?of 53%,and PCE of 10.50%.Meanwhile,the HC?N H₂?₂PbI₃ lead based perovskite thin film solar cells demonstrated the maximum Jsc of 15mA/cm2,as well as Voc of 0.61 V,FF of 25%,and PCE of 2.3%.The photovoltaic performance of lead based perovskite thin film solar cel s is going to be improved by optimizing functional layers in the devices.