Graded Heterojunction Improves Wide-Bandgap Perovskite for Highly Efficient 4-Terminal Perovskite/Silicon Tandem Solar Cells

Wide-bandgap(WBG)perovskite solar cells(PSCs)are essential for highly efficient and stable silicon/perovskite tandem solar cells.In this study,we adopted a synthetic strategy with lead thiocyanate(Pb(SCN)_(2))additive and methylammonium chloride(MACl)posttreatment to enhance the crystallinity and improve the interface of WBG perovskite films with a bandgap of 1.68 eV.The excessive PbI_(2)was formed at grain boundaries and converted into MAPbI_(3-x)Cl_(x)perovskites,which are utilized to form the graded heterojunction(GHJ)and compressive strain.This is beneficial for passivating nonradiative recombination defects,suppressing halide phase segregation,and facilitating carrier extraction.Subsequently,the device with GHJ delivered a champion efficiency of 20.30%and superior stability in ambient air and under 85℃.Finally,we achieved a recorded efficiency of 30.91%for 4-terminal WBG perovskite/TOPCon tandem silicon solar cells.Our findings demonstrate a promising approach for fabricating efficient and stable WBG PSCs through the formation of GHJ.