Surface charge-transfer doping for highly efficient perovskite solar cells

Nonradiative recombination losses are the predominant reason that limits the full thermodynamic potential of perovskite solar cells (PSCs), mainly originating from surface defects and interfacial energetics. However, their synergies between the two key factors are poorly understood. Herein, we systemically explore the energetic role of ionic liquid defect-passivator Tetrabutylammonium hexafluorophosphate (TBAPF₆) on n-i-p planar PSCs. The perovskite film surface has been transformed from p-type to n-type after TBAPF₆ modification, evidenced by a shift of Fermi level closer to the conduction band. The n-type energetics result in a higher density of electron carrier and a smaller electron extraction barrier at perovskite/PCBM interface, promoting charge transport. It is also shown that the perovskite film can undergo a clear transformation from n-type to p-type character as increasing work function of substrates. Further studies clearly illustrate that TBAPF₆ not only reduces the surface defect-assisted recombination, but also restrains the interface carrier recombination. These combined effects lead to the effective suppression of nonradiative recombination, attributing to a significant improvement in the device power conversion efficiency.