The Effect Of Low-temperature Solution Processed Electron Transport Layers On The Property Of The N-i-p Perovskite Solar Cells

Solar energy is a kind of inexhaustible renewable energy;it is significant for the optimization of energy structure and improvement on ecological environment.Photovoltaic power generation is the main way of solar energy utilization.Solar cell is the basic unit of photovoltaic power generation system.In recent years,representative perovskite materials(CH3NH3PbX3(X=Cl,Br,I))have received great concern from solar cell researchers.Perovskite materials have been used as light-absorbing layers for solar cells owing to their high light absorption coefficient,long carrier diffusion length and appropriate bandgaps.Up to now,the power conversion efficiencies(PCEs)of perovskite solar cells(PSCs)have been improved to 23.7%.Electron transport layers(ETLs)are significant to perovskite solar cells,because they play crucial roles in extracting photo-induced carriers while suppressing their recombination.Therefore,property of the ETLs is important in improving performance of the PSCs.It is well known that C60 shows superior electron mobility and appropriate conduction band.Notably,unlike most oxides,C60 does not require high-temperature sintering.Thus it has been successfully used as electron transport materials in n-i-p planar heterojunction PSCs(PHJ-PSCs).Normally,C60 was used as an interface modifier of metal oxide ETL/perovskite to improve the performance of PSCs.However,high-temperature process is commonly required for preparing metal oxide film.Such high temperature hampers the development of PSCs on flexible and monolithic tandem devices.However when low-temperature solution processed C60 was used as independent ETL,surface wettability of the substrate is inferior,this leads to poor performance of PSCs.In this study,firstly,we applied solid-state ionic-liquid(1-ethyl-3-methylimidazolium iodide([EMIM]I))and C60 as independent ETL in n-i-p PHJ-PSCs at low temperature,their effects on photoelectric properties of n-i-p PHJ-PSCs and their drawbacks were investigated respectively.Then we modified solution-processed C60 ETL with solid-state ionic-liquid(IL)at low temperature.As the result,first,the work function of substrate was reduced and thus leads to a more favorable energy-level alignment;Second,the charge-carrier transfer was enhanced and the charge recombination was suppressed,simultaneously;third,the wettability between the precursor solution and the substrate was improved and thus leads to more smooth and continuous perovskite films.Using this interface modification method at low temperature,we fabricated n-i-p PHJ-PSCs based on FTO/IL/C60 and FTO/IL/C60/IL structures respectively.When CH3NH3PbI3 perovskite materials were used as absorption layers of PSCs,through further optimizing the fabricated methods of ETLs,an optimized PCE of 15.09%was obtained in n-i-p PHJ-PSCs,with a short circuit current density of 22.61 mA/cm2,an open circuit voltage of 0.94V,and a fill factor of 71.12%.