Ambient-Air Fabrication And Interfacial Regulation Of Perovskite Absorber In Perovskite Solar Cells

The perovskite solar cells(PSCs),which integrate the superb photovoltaic performance and low-cost fabrication,have drawn much attention in the photovoltaic community.In a typical PSC,the perovskite absorber layer is sandwiched between electron and hole transporting layers,where the quality of perovskite absorber,such as surface morphology,crystal structure,absorbance feature,defect density etc.,greatly influences the device performance.After a decade of development,high-quality perovskite thin films can be reproducibly synthesized by solvent engineering strategy combined with anti-solvent scouring treatment and additive engineering method.Over 24%power conversion efficiency(PCE)has been achieved based on this routine.However,this strategy is normally manipulated under inert atmosphere in order to avert the adverse influence of moisture on crystallization.As a more appealing strategy for low-cost and large-scale production of PSCs,ambient-air fabricating strategy is much less studied.Besides the intrinsic properties of the perovskite absorber,carrier loss at the interface between perovskite layers and charge transporting layers(CTLs)is also a major efficiency limitation in the state of the art cells.Aiming at the enhancement on PCE and stability of the PSCs,the ambient-air fabrication and interfacial passivation are investigated in this thesis.The results are as follow:(1)Ambient-air fabrication of the MAPbI3 perovskite film.A novel statical anti-solvent-scouring procedure is introduced during the fabrication of MAPbI3 films by solvent engineering strategy(static method),which obviously improves the poor ambient-air crystallization of the films induced by the traditional dynamical manner.XRD analysis demonstrates the highly preferred orientation of the perovskite intermediate films fabricated by the static method,which consume much shorter time to convert to the perovskite films.The defect density of the as-prepared MAPbI3 film is reduced compared with films fabricated by the traditional dynamic manner,leading to the suppression of nonradiative recombination in the corresponding films,as proved by the Urbach energy(Eu)calculation and photoluminescence analysis.The PSCs based on the MAPbI3 films fabricated by static method show apparent enhancements on the short-circuit current density(Jsc)and fill factor(FF),which contribute to the 16.1%of PCE,much higher than the 14.3%of the PSCs based on traditional dynamic manner.(2)Ambient-air fabrication of the FAPbI3 perovskite film.A novel Lewis base N-methylpyrrolidone(NMP)is introduced to fabricate FAPbI3 film under ambient air,during which the formation of a stable FAI·PbI2-NMP intermediate alters the traditional FAPbI3 crystallization routine.It demonstrates that the FAPbI3 film transformed from FAI·PbI2-NMP intermediate exhibits a more uniform surface with the elimination of none-perovskite isomer,significantly improving the poor crystallization induced by traditional Lewis bases.Thus,a reduced defect density,improved carrier migration rate and prolonged carrier lifetime are achieved in the FAPbI3 film from NMP method.The PSCs based on FAPbI3 films produce with NMP Lewis base delievers a best PCE of 17.3%,more than 10%enhancement compared to device fabricated from traditional method.After 30-day ambient air storage,a decent PCE of 13.6%is retained.(3)Passivation on the perovskite film/charge transporting layer interface.A novel interface engineering strategy based on dissolution-recrystallization process of[6,6]-phenyl-C61-butyric acid methyl ester(PCBM)passivator is developed to regulate the properties of the perovskite film/charge transporting layer interface.Negligible influence on the wettability of perovskite precursor solution and quality of the as-prepared perovskite films is induced by our passivating method,enabling it outstands among the other PCBM-based passivating strategies.The characterization carried out on film-and device-level demonstrates that a bottom-up PCBM gradient is established through the dissolution-recrystallization process,which effectively optimizes the interfacial band alignment.Meanwhile,the PCBM passivator can in situ react with the defect sites,leading to the reduction of the trap state density and suppression of the nonradiative recombination.The champion PSCs passivated by the dissolution-recrystallization process shows significantly improved efficiency and stability,which delivers a PCE of 20.1%and retained 91%of initial efficiency after 35-day storage.