Study On The Influence Of Encapsulation And A-site Cations On The Stability Of Perovskite Solar Cells

Perovskite solar cells have attracted great attentions due to their rapid improvement on power conversion efficiency,which has soared from 3.8%to 23.7%within last ten years.But the poor long term stability inhibits its futher applications.Perovskite materials are easy to decompose under moisture,oxygen,heat and light illumination conditions,resulting in irreversible decrease in power conversion efficiency.At present,it is the biggest challenge to overcome the stability issue of perovskite solar cells.In this thesis,we focus on the stability of perovskite solar cells,mainly involving encapsulation of perovskite solar cells via magnetron sputtering,exploration the influence of A site cation of perovskite solar cell under heat or light illumination conditions.The main research contents and conclusions are summarized as following:1.Based on the FTO/SnO₂/MAPbI₃/Spiro/Au planar n-i-p device structure,the thermal evaporation/magnetron sputtering method was used to achieve thin film encapsulation of perovskite solar cells.The influence of magnetron sputtering on the device performances was investigated.We found that an evaporated M_OO₃ layer could effectively minimize the damage from magnetron sputtering.When M_OO₃ thickness is50 nm,the damage can be less than 5%.We found Al₂O₃ owns the best barrier property due to its uniform surface and best hydrophobicity among three commonly used materials,Al2O3,SiO2 and SiNx.The device with Al2O3 encapsulation could retain 83%of its initial efficiency after a week kept in 30?,60%RH,dark conditions,where the unencapsulated device's efficiency degraded more than 50%efficiency even after 8hours.2.Based on FTO/SnO₂/APbI₃/C device architecture,we investigated the thermal stability of perovskite solar cells with four A-site cations(MAPbI3,FAPbI3,FA_0.6MA_0.4PbI₃ and FA_0.9Cs_0.1PbI₃,labeled as MA,FA,FM,FC,respectively),The testing conditions are the stability under 85? and thermal cycling?from-30? to85?,200 cycles?conditions.After 200 hours under 85? in N₂ atmosphere,MA,FA,FM,FC devices retained 24%,43%,58%and 73%of their initial efficiency,respectively.Our results suggested that FC perovskite was more resistant to thermal decompose.Besides,MA,FA,FM,FC devices with encapsulation retained 9%,41%,48%and 88%of their initial efficiency after 200 thermal cycles testing,respectively.Our results indicated that MA perovskite suffered cubic to tetragonal phase transition,FM and FA perovskites suffered?to?phase transition,only FC perovskite had well stayed its photoactive?-phase.Above all,FC perovskite solar cell owns preferable thermal stability.3.Based on FTO/SnO₂/APbI₃/Spiro/Au device structure,we investigated the light illumination stability of perovskite solar cells?MA,FM,FC?with three A-site cations.When temperature is 20?,MA,FM,FC devices retained 65%,75%,86%of their initial efficiency after 24 hours'light illumination.When temperature is 50?,MA,FM,FC devices retained 17%,57%,60%of their initial efficiency after 12 hours'light illumination.Our result indicated that FC device was more stable,but also suffered significant degradation.