The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and mixed halide anions. The concentration of defect states, which reduce a cell's performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.
Tin
oxide (SnO2) has recently emerged as a promising
electron transport layer for perovskite solar cells (PSCs) in light
of the material’s optical and electronic properties and its
low-temperature processing. However, SnO2 films are prone
to surface defect formation, which results in energy loss in PSCs.
We report that surface treatment using ammonium fluoride (NH4F) leads to reduced surface defects and that it also induces chemical
doping of the SnO2 substrate simultaneously. The effects
of NH4F treatment on SnO2 properties are revealed
by surface chemical analysis, computational studies, and energy level
investigations, and PSCs with the treatment achieve photovoltaic performance
of 23.2% in light of higher voltage than in relevant controls.
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