Groups-dependent phosphines as the organic redox for point defects elimination in hybrid perovskite solar cells

Lead (Pb)0 and iodine (I)0 point defects generated during perovskite solar cell (PSC) fabrication and photoconversion form deep band energy levels as the carriers’ recombination centers. These defects not only deteriorate device efficiency, but also facilitate chemical degradation with ion migration, resulting in restricted device lifetime. Herein, we present a novel type of phosphines as the point defects stabilizer for hybrid perovskite solar cells with enhanced performances. Three phosphines with varied side groups of tributyl, trioctyl and triphenyl are exampled as the dopants in perovskite films. The group dependent redox properties were observed in the perovskite film, dependent on their molecular weights and steric hinderances of phosphines. The partially oxidized tributyl phosphine (TBUP) with additional tributyl phosphine oxides (TBPO) is efficient in reduction of lead (Pb)0 and iodine (I)0 concentrations during the device fabrication and operation. The device with TBUP-TBPO pair showed enhanced power conversion efficiency (PCE) to 20.48% and maintain 91.7% of their initial PCEs after 500 h at 65 °C thermal annealing. Thus, this work presents an efficient route of utilize the phosphine species to reduce point defects in the perovskite film, which promoting further development of novel phosphorous additives with defects stabilization, interface passivation and encapsulation for low-cost solution processed PSCs.