Diamine Surface Passivation and Postannealing Enhance the Performance of Silicon-Perovskite Tandem Solar Cells
Margherita Taddei, Hannah Contreras, Hai-Nam Doan, Declan P. McCarthy, Seongrok Seo, Robert J. E. Westbrook, Daniel J. Graham, Kunal Datta, Perrine Carroy, D. Muñoz, Juan‐Pablo Correa‐Baena, Stephen Barlow, Seth R. Marder, Joel A. Smith, Henry J. Snaith, David S. Ginger
Abstract
We show that the use of 1,3-diaminopropane (DAP) as a chemical modifier at the perovskite/electron-transport layer (ETL) interface enhances the power conversion efficiency (PCE) of 1.7 eV band gap mixed-halide perovskite containing formamidinium and Cs single-junction cells, primarily by increasing the open-circuit voltage ( V OC ) from 1.06 to 1.15 V. We find that adding a postprocessing annealing step after C60 evaporation further improves device performance. Specifically, the fill factor (FF) increases by 20% in the DAP + postannealing devices compared to the control. Using hyperspectral photoluminescence microscopy, we demonstrate that annealing helps improve compositional homogeneity at the electron-transport layer (ETL) and hole-transport layer (HTL) interfaces of the solar cell, which prevents detrimental band gap pinning in the devices and improves C 60 adhesion. Using time-of-flight secondary ion mass spectrometry, we show that DAP reacts with formamidinium (FA + ) present at the surface of the perovskite structure to form a larger molecular cation, 1,4,5,6-tetrahydropyrimidinium (THP + ), which remains at the interface. Combining the use of DAP and annealing the C 60 interface, we fabricate Si-perovskite tandems with a PCE of 25.29%, compared to 23.26% for control devices. Our study underscores the critical role of the chemical reactivity of diamines at the surface and the thermal postprocessing of the C 60 /Lewis-base passivator interface in minimizing device losses and enhancing solar-cell performance of wide-band-gap mixed-cation mixed-halide perovskites for tandem applications.