Investigation On Fabrication And Interfacial Engineering Of Perovskite Solar Cells Based On Carbon Electrodes

Due to the excellent optical and electrical properties of perovskite materials,the certified efficiency of perovskite solar cells(PSCs)has reached 25.5%at present,showing broad application prospects.Carbon materials have the advantages of low cost,high chemical stability and strong hydrophobicity.Carbon electrodes can simultaneously replace noble-metal top electrodes and hole transport materials,and have a certain encapsulation effect on PSCs.Therefore,the development of perovskite solar cells based on carbon electrodes(C-PSCs)can reduce the cost and enhance the stability of the device,which is an important strategy to solve the issues of high cost and low stability of PSCs.However,in comparison with conventional PSCs,C-PSCs have poor photovoltaic performance and low open-circuit voltage due to the serious energy loss in the carrier dynamic process.This is manifested as:on the one hand,the rough surface morphology of the carbon materials leads to poor physical contact at the perovskite/carbon electrode interface,giving rise to difficluty in carrier extraction and serious recombination problem;on the other hand,there is a larger energy level difference between the work function of the carbon electrode and the valence band maximum of the perovskite.This leads to insufficient driving force to facilitate carrier separation and extraction,resulting in excess recombination of charge carriers and the low hole-collection efficiency at the interface.In view of the core scientific problems mentioned above,the researches on the development of carbon electrode and the interfacial engineering between perovskite and carbon electrode are carried out in this work.The main research contents are as follows:(1)Research on ultra-low-cost coal-based carbon electrode:For the problem of complex synthesis process and high price of some carbon-based electrode materials(such as carbon nanotubes and graphene),the ultra-low-cost coal-based carbon is synthesized using coal powder as raw material.Its price is only 1/36 that of the cheap carbon black.Through optimizing the fabricating process,the C-PSCs with a coal-based carbon electrode obtain an efficiency of 10.87%on the active area of 0.3 cm2,and the efficiency of 8.72%is achieved on a larger area of 1 cm2.In addition,the stability of the C-PSCs is significantly improved in comparison with traditional PSCs.After storage for 120 h in ambient air,the efficiency of coalcarbon electrode C-PSCs without encapsulation only dropped by 15.6%.(2)Investigation on interfacial engineering to improve the extraction and transfer of carrier:For the interfacial problems between the perovskite and the carbon electrode caused by the rough surface morphology of carbon materials,including the poor physical contact,the difficluty in carrier extraction,and the serious recombination,a dynamic and in-situ interfacial engineering strategy is explored.Through this in-situ interfacial engineering,the favourable electrical contact is achieved between the perovskite and the carbon electrode using acetylene black.Carrier dynamic studies show that the rapid hole extraction and transport are achieved at the perovskite/carbon electrode interface,and the recombination of electrons and holes is suppressed.The efficiency of C-PSCs reaches 16.41%,and the efficiency is 14.03%on a larger area of 1 cm2.Stability studies indicate that the hydrophobicity of the perovskite layer is enhanced,and the perovskite decomposition induced by moisture is inhibited as a result of the intimate interfacial contact.After storage for 2000 h in ambinent air at 30℃ and 30%relative humidity(RH),the C-PSCs without any encapsulation could keep 93%of their initial efficiency.And after storage for 312 h in hostile air environment at 85℃ and 65%RH,the C-PSCs without any encapsulation could maintain 81%of their initial efficiency.(3)Research on improvement in the open-circuit voltage of C-PSCs by energy level matching and interfacial passivation:For the issue of energy level mismatch at the perovskite/carbon electrode interface,CuSCN is used as a hole transport layer,and intercalated between the perovskite and the carbon electrode to optimize the energy level alignment.And the interfacial passivation is performed to improve the carrier transfer performance and physical contact of the perovskite/CuSCN interface.Carrier transfer dynamics show that the synergistic effect of energy level matching and interfacial passivation facilitates the extraction and transfer of holes between perovskite and carbon electrode,suppresses the recombination of electrons and holes,and enhances hole collection,which is beneficial to reduce the open-circuit voltage loss of C-PSCs.Due to the good energy level matching,the improved carrier transfer and the enhanced physical contact,open-circuit voltage of C-PSCs increases from 0.98 V to 1,078 V,and the efficiency reaches 15.81%.After storing for 2000 h in ambient air,the C-PSCs without encapsulation retain 93%of the initial efficiency.And after storing for 300 h in air atmosphere at 85℃ and<10%RH,the encapsulated C-PSCs keep 83%of the initial efficiency.(4)Investigation on ammonium salt-modified CuSCN to boost the efficiency of interfacial hole collection:For the poor film quality of CuSCN,the pinholes of the film lead to the hole accumulation,the recombination of electrons and holes,and the low efficiency of hole collection.Organic ammonium salt(phenethylammonium iodide)is used to modify CuSCN for improving the film quality,passivating the defects of the perovskite,and enhancing the interfacial contact with the perovskite.Carrier transfer dynamics indicate that the extraction and transport of holes at the perovskite/CuSCN interface are improved because of the ammonium salt modification,which is favorable to boost the hole-collection efficiency.The efficiency of C-PSCs with modified CuSCN is increased by～11%.After storage for 800 h in air at 18-22℃ and 60%-70%RH,the C-PSCs retain 70%of the initial efficiency.