The Effect Of A PCBM Electron Transport Layer Containing Additives On The Performance Of Perovskite Solar Cells

Since June 2013,hybrid organic/inorganic halide perovskite solar cells(PSCs)have attracted much research attention due to their superb and rapidly improving performance.The PSCs was rated as one of the top ten international scientific and technological advances by Science in 2013.PSCs composed of organic-metal-halide materials have made impressive progress in just a few years with maximum power conversion efficiencies(PCEs)evolving from 3.8%in 2009 to a certified 22.1%in 2016.Increasing the photoelectric conversion efficiency of PSCs is always the subject of constant change in the research and development of photovoltaic devices.Previous approaches to increasing the PCE of PSCs have focused on optimization of the morphology of perovskite films.However,there are relatively few studies on the electron transport layer(ETL)in the typical p-i-n sandwich structure.The electron transporting material and the absorbing layer plays an important role in improving the photoelectric conversion efficiency in PSCs,Especially in the orthostructure device.At the same time,the properties of charge transport of the electron transport layer have a critical effect on PSCs performance,and the chemical properties and their interfaces also affect the stability and life of the PSCs.In this work,we have successfully improved the morphology of the electron transport layer and the quality of the film and the properties of charge transport of the electron transport layer,and get a better efficiency of PSCs by using polystyrene(PS)and 1,8-diiodooctane(DIO)as binary additives during the deposition of phenyl-C61-butyric acid methyl ester(PCBM)layer.Fristly,We prepared the structure of ITO/PEDTO:PSS/CH3NH3PbI3/PCBM/Al devices,The effect of the additive 1,8-diiodoctane(DIO)on the performance of the photovoltaic device was investigated by changing the concentration of the additive.The PCE of PSCs was improved from 10.73%to 12.06%,the short-circuit current density(Jsc)was improved from 15.555 mA·cm-2 to 16.347 mA·cm-2,the open-circuit voltage(Voc)was improved from 0.95 V to 0.98V by using 2%DIO as a solvent additive during the deposition ofPCBM layers.The addition of DIO improves the morphology of PCBM,which plays an important role in charge dissociation,charge transportation,and charge collection.This result can be explained by the higher boiling point(333 ℃)of DIO compared to that of the host solvent(CB;132℃).During the growth of the PCBM layers(byspin-coating and thermal annealing),DIO inhibits the rapidevaporation of CB,which is a low boiling point solvent,Which is beneficial to enhance the crystal quality of PCBM,and result in a well-packed PCBM morphology,Thereby improve the properties of charge transport of the electron transport layer.Secondly,We used PS as the second additive with DIO as binary additives during the deposition of phenyl-C61-butyric acid methyl ester(PCBM)layer,which can combine the advantages of both to achieve better results.The polystyrene(PS)is often used as an additive in the active layer of organic solar cells to enhance the solution viscosity and increase the thickness of the film to enhance the uniformity of the film,There are also reports about using PS as an additive to the electron transport layer PCBM in PSCs.The addition of PS facilitates the formation of a highly smooth and uniform PCBM ETL that is more effective in preventing undesirable electron-hole recombinationbetween the perovskite layer and the top electrode.The PCE of PSCs was improved from 10.8%to 12.5%by using polystyrene(PS)and 1,8-diiodooctane(DIO)as binary additives during the deposition of phenyl-C61-butyric acid methyl ester(PCBM)layer,which is better than the performance of single additive treatment.Our results indicate that the addition of two additives is a simple and low-cost approach to improving the morphology of the electron transport layer providing a path to further increase the performance of p-i-n PSCs.