Investigation On The Performance Of Perovskite/Crystalline Silicon Tandem Solar Cells Using Ultrathin Silver Transparent Electrodes

Tandem solar cells,using high bandgap top cells combined with narrow bandgap bottom cells,can reduce the thermalization loss for high energy photons and sub-bandgap loss for low energy photons,thus improving the power conversion efficiency(PCE)of the solar cells.Recently,tandem solar cells using perovskite solar cells(PSCs)as the top cells have attracted great attention due to the rapid progress in power conversion efficiency.Ultrathin silver(Ag)films,featuring cost-effective and low energy preparation,as well as good electrical conductivity and optical transparency,are believed as promising candidates as transparent electrodes for semitransparent PSCs.However,the low transmittance in the near infrared wavelength range for the ultrathin silver electrodes restricts the PCEs of bottom cells as well as tandem cells.In this paper,continuous Ag films with percolation threshold lower than 6 nm were realized through Cu seed layer.The performance of semitransparent PSCs using ultrathin Ag films as transparent electrodes was investigated.Ultimately,four-terminal tandem solar cells using semitransparent PSC and homogenous crystalline silicon solar cell were demonstrated.The main contents of this paper are as follows:1.The effect of Cu seed layer on the growth behavior and optoelectrical characteristics of ultrathin Ag films were studied.The percolation threshold thickness of continuous Ag films was reduced to 5 nm by introducing 1 nm Cu seed layer.As a result,5 nm Ag films possessed low surface roughness(RMS=0.241 nm),broadband transparency(T_ave(400-1200 nm)=70.46%),and high conductivity(R_s=32?/sq).However,further reducing Cu seed layer thickness from 1 nm to 0.5 nm almost had no effect on the optoelectrical characteristics of ultrathin Ag films.2.The ultrathin Ag films were applied as transparent electrodes of perovskite solar cells,and the effect of Ag film thickness on the performance and optical properties of perovskite cells was studied.It was found that the PCE of the semitransparent PSC using Cu(1 nm)/Ag(6 nm)electrode was 14.5%,maintaining 88%PCE of the reference cells using thick Ag electrodes.By further introducing the Zn O optical coupling layer,the average transmittance of the semitransparent PSC in the wavelength range of 800-1200 nm was increased to 58.6%,thus guaranteeing high PCE of the filtered bottom cells.Finally,the PCE of the four-terminal tandem solar cell using semitransparent perovskite top cell and homogeneous crystalline silicon bottom cell was 19.0%,higher than that of either sub-cell.In addition,the strategies such as using the 5 nm Ag electrodes combining with the Ag grids,and adopting the optical coupling layer with higher refractive index,are proposed to further improve the power conversion efficiency of tandem solar cells.