| The efficiency of perovskite solar cells has been increased from less than 4%to 23.3%since 2009.In just 9 years,the efficiency of the perovskite solar cell is promoted to almost as high as that of the crystalline silicon solar cells,which was taken about half a century.The rapid development is mostly contributed to the special structure of the perovskite materials.In general,the perovskite can be described using a general chemical formula ABX3,in which each octahedral BX6 unit shares the X atoms as the vertice to form the 3D structure,and A is located at the body-center in the cube formed by eight neighboring BX6 units to hold the overall structure together.This special structure shows excellent optoelectronic properties,in particular,it displays an adjustable band gap by doping different elements,large absorption coefficient,high carrier mobility,ultra-low trap density and long carrier life time.Although the perovskite solar cell shows the speedily development,its flexible counterpart exhibits relative slower progress,mostly limited by its electron transport layer(ETL)that prefers high temperature treatment that is not compatible with the polymeric substrates.In fact,the common ETL needs a heat treatment at 300?400? in order to achieve its best performance,much higher than what the common polymeric materials can withstand.In view of above issues,we developed a low temperatue ETL for high performance flexible perovskite solar cells.In addition,using optimized perovskite absorber layer,we achived record high efficiency for the flexible cells.More specifically,our developments may be summarized as follows:?.A few methods have been developed for the high performance ETL layer.Even though we could prepare high efficiency perovskite solar cells using the common TiO2 ETL fabricated using a chemical bath deposition(CBD),its high temperature treatment and the UVO process make it not suitable for flexible PET substrate.In order to overcome the problem,we developed an effective Nb2O5 based ETL using e-beam evaporation at low substrate temperature.?.Using the Nb2O5 ETL,we designed and fabricated flexible perovskite solar cell.The experimental results reveal that different thickness of Nb2O5 films show different optical and electrical properties,with the highest cell efficiency achieved when the Nb2O5 film is controlled at 60 nm in thickness.The low temperature process allows us to fabricate flexible perovskite solar cells,with cell efficiency reaching 15.56%for small area of 0.09 cm2 cells and and 14.03%for large area 0.25 cm2 cells?.Using methyl sulfide as an effective additive,we further improved the flexible perovskite cell efficiency.The results show that different volume ratio of additive lead to the different cell efficiency,with the optimized performance achieved at volume ratio at 10%.It is found that the additive aids to increase grain size,improved crystalline quality,reduce trap density in the absorber layer.As a result,the efficiency of flexible perovskite solar cells is raised up to 18.40%,the highest efficiency reported to date for the flexible perovskite devices?.We developed the Octyl mercaptan as an additive to improve the quality of the CS0.05FA0.95PbI3 film.With reduced tap density and larger grain size,we obtained 22.43%-efficiency for rigid perovskite solar cell using Zinn mercaptan additive,with eliminated hysteresis.Moreover,the cells show very good stability with 90%of efficiency remained after 90 days of storage under 30%humidity. |
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