Deeper Insight into the Role of Organic Ammonium Cations in Reducing Surface Defects of the Perovskite Film

Abstract

Organic ammonium salts (OASs) have been widely used to passivate perovskite defects. The passivation mechanism is usually attributed to coordination of OASs with unpaired lead or halide ions, yet ignoring their interaction with excess PbI 2 on the perovskite film. Herein, we demonstrate that OASs not only passivate defects by themselves, but also redistribute excess aggregated PbI 2 into a discontinuous layer, augmenting its passivation effect. Moreover, alkyl OAS is more powerful to disperse PbI 2 than a F-containing one, leading to better passivation and device efficiency because F atoms restrict the intercalation of OAS into PbI 2 layers. Inspired by this mechanism, exfoliated PbI 2 nanosheets are adopted to provide better dispersity of PbI 2 , further boosting the efficiency to 23.14 %. Our finding offers a distinctive understanding of the role of OASs in reducing perovskite defects, and a route to choosing an OAS passivator by considering substitution effects rather than by trial and error.

Modulating Residual Lead Iodide via Functionalized Buried Interface for Efficient and Stable Perovskite Solar Cells

“…A higher recombination resistance ( R rec ) was obtained for the DDSI 2 device (59 kΩ) than for the pristine device (29 kΩ), illustrating reduced carrier recombination loss . Furthermore, the W F value of the DDSI 2 perovskite film is higher than that of the pristine film, as can be seen from a UPS characterization (Figure S21) and Kelvin probe force microscopy (KPFM) (Figure S22), which may be attributed to the redistribution of p-type PbI 2 which increases its contact area with the surface of the perovskite film . The higher W F may lead to a type II band alignment at the HTL/perovskite interface, which allows hole transfer from the perovskite layer to PbI 2 but intercepts electron transfer. ,, …”

“…Interestingly, based on the SnO 2 /DDSI 2 substrate, the PbI 2 is regularly and uniformly distributed on the surface of perovskite grains, and the size of PbI 2 (∼80 nm) is also significantly reduced from ∼500 nm. The size reduction of PbI 2 may enhance its passivation. , Compared with the 0.87 μm grain size of the pristine film, the average grain size of the DDSI 2 film was increased to 1.23 μm (Figure S12). The absorption of the film was characterized by an ultraviolet–visible (UV–vis) spectrophotometer.…”

“…There have been few systematic studies on the distribution of PbI 2 on the surface of perovskite grains. Moreover, previous literature on the morphology and distribution of PbI 2 was mainly focused on perovskite precursor solution additives and postprocessing of perovskite films. − It is worth noting that the buried interface is also one of the primary factors affecting the quality of perovskite films and residual PbI 2 , but its importance is often overlooked. − …”

“…The size reduction of PbI 2 may enhance its passivation. 24,36 Compared with the 0.87 μm grain size of the pristine film, the average grain size of the DDSI 2 film was increased to 1.23 μm (Figure S12). The absorption of the film was characterized by an ultraviolet−visible (UV−vis) spectrophotometer.…”

“…21 Furthermore, the W F value of the DDSI 2 perovskite film is higher than that of the pristine film, as can be seen from a UPS characterization (Figure S21) and Kelvin probe force microscopy (KPFM) (Figure S22), which may be attributed to the redistribution of p-type PbI 2 which increases its contact area with the surface of the perovskite film. 24 The higher W F may lead to a type II band alignment at the HTL/perovskite interface, which allows hole transfer from the perovskite layer to PbI 2 but intercepts electron transfer. 16,22,36 Based on the results obtained by the modification strategy of DDSI 2 and the uniformly distributed PbI 2 nanosheets, the device structure diagram and the carrier transport simulation diagram can be seen in Figure 6a.…”