Reducing Surface Recombination Velocity of Methylammonium-Free Mixed-Cation Mixed-Halide Perovskites via Surface Passivation

• Published in: Chemistry of materials Vol. 33; no. 13; pp. 5035 - 5044
• Main Authors: Jariwala, Sarthak, Burke, Sven, Dunfield, Sean, Shallcross, R. Clayton, Taddei, Margherita, Wang, Jian, Eperon, Giles E, Armstrong, Neal R, Berry, Joseph J, Ginger, David S
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 13.07.2021; American Chemical Society (ACS)
• Subjects: Passivation; Perovskites; Recombination; SOLAR ENERGY; Surface passivation; Thin films
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.1c00848

We control surface recombination in the mixed-cation, mixed-halide perovskite, FA0.83Cs0.17Pb­(I0.85Br0.15)3, by passivating nonradiative defects with the polymerizable Lewis base (3-aminopropyl)­trimethoxysilane (APTMS). We demonstrate average minority carrier lifetimes >4 μs, nearly single exponential monomolecular photoluminescence decays, and high external photoluminescence quantum efficiencies (>20%, corresponding to ∼97% of the maximum theoretical quasi-Fermi-level splitting) at low excitation fluence. We confirm both the composition and valence band edge position of the FA0.83Cs0.17Pb­(I0.85Br0.15)3 perovskite using multi-institutional, cross-validated, X-ray photoelectron spectroscopy and UV photoelectron spectroscopy measurements. We extend the APTMS surface passivation to higher bandgap double-cation (FA and Cs) compositions (1.7, 1.75, and 1.8 eV) as well as the widely used triple-cation (FA, MA, and Cs) composition. Finally, we demonstrate that the average surface recombination velocity decreases from ∼1000 to ∼10 cm/s post APTMS passivation for FA0.83Cs0.17Pb­(I0.85Br0.15)3. Our results demonstrate that surface-mediated recombination is the primary nonradiative loss pathway in many methylammonium (MA)-free mixed-cation mixed-halide films with a range of different bandgaps, which is a problem observed for a wide range of perovskite active layers and reactive electrical contacts. Our study also provides insights to develop passivating molecules that help reduce surface recombination in MA-free mixed-cation mixed-halide films and indicates that surface passivation and contact engineering will enable near-theoretical device efficiencies with these materials.