Research On The Effect Of Interface Modification On The Performance Of Perovskite Solar Cells

Solar energy is an ideal energy source that is clean and pollution-free.The energy radiated to the earth every year has reached several orders of magnitude of global energy consumption.Current solar cell technology limits the utilization of solar energy.Perovskite solar cells（PSCs）are characterized by low cost and high performance.The power conversion efficiency（PCE）of single-junction PSCs in the laboratory has exceeded 25%.However,the commercialization process of PSCs has encountered many challenges,among which the problem of interface recombination is the most prominent,resulting in a serious loss of PCE in a short period of time.Fortunately,interface engineering technology has been seen as an effective means to achieve better energy level alignment,reduce carrier recombination,passivation defects,eliminate photocurrent hysteresis,and enhance long-term stability of device.This thesis focuses on improving the efficiency and long-term stability of PSCs,using interface engineering to separately treat the electron transport layer（ETL）/perovskite layer and the perovskite layer/hole transport layer（HTL）interface,thereby improving device efficiency and stability.First,the effect of polymethyl methacrylate（PMMA）interface modification layer on the performance of PSCs was studied.An ultra-thin PMMA layer was introduced into the perovskite/Spiro-OMe TAD interface to passivate the interfacial and intercrystalline defects.After passivation,the open circuit voltage（Voc）reached 1.18 V and showed a steady-state PCE of 20.5%.A series of characterization results confirmed that the non-radiative recombination of the passivation device was effectively inhibited,and the carrier concentration also showed significant increased.In addition,the PMMA film can protect the perovskite film from the moisture and oxygen.Under environmental conditions with a relative humidity of 60%,the unsealed device can still maintain an initial efficiency of 95%after one month.This method solves one of the main limitations of interface recombination and shows great potential for improving the performance of PSCs in the future.Secondly,the hydrophilic polymer polyethylene glycol（PEG）was compounded with phenyl-C61-methyl butyrate（PCBM）to obtain a composite material with good wettability（PEG-PCBM）,which was used to modify ETL/Perovskite interface.As a result,PEG-PCBM modified ETL exhibits increased surface energy,which is conductive to the preparation of high-quality perovskite films with large-size.NMR results show that there are hydrogen bondsg between the PEG-PCBM buffer layer and the perovskite layer,which is beneficial to further stabilize the ETL/perovskite interface.Thanks to improvement of electron transport performance and the suppression of carrier recombination,a device with an effective area of 1.03 cm~2 achieve an efficiency of 18.25%.In addition,first-principles calculations show that PEG has stronger adsorption(E_ads=-0.37)to water molecules than perovskite(E_ads=-0.25),which can prevent water molecules from penetrating into the perovskite layer.Under environmental conditions with a relative humidity of 30-40%,the unsealed device still retains 90%of the initial PCE after storage for 22 days.These outstanding properties are attributed to the unique molecular structure and superior wettability of PEG.Finally,based on the formamidine-rich（FA-rich）perovskite light absorption layer,the effect of the modified layer of cesium trifluoroacetate（Cs TFA）on the performance of PSCs was studied.By introducing a Cs TFA modification layer at the perovskite/HTL interface,the iodine vacancies can be effectively passivated by TFA^-,and cesium ions can fill the formamidine vacancies,thereby inhibiting carrier recombination and ion migration,result in significantly improved photovoltaic performance and operation stability of the device.In addition,the small size of cesium ions can induce surface lattice shrinkage and increase the phase stability of FAPb I₃ perovskite.As a result,the modified device showed a PCE of 21.6%,and retained more than 90%of the initial PCE after the AM1.5 simulated sunlight continuously irradiated for 1000 hours.