Understanding the Effect of Lead Iodide Excess on the Performance of Methylammonium Lead Iodide Perovskite Solar Cells

Abstract

The presence of unreacted lead iodide in organic−inorganic lead halide perovskite solar cells is widely correlated with an increase in power conversion efficiency. We investigate the mechanism for this increase by identifying the role of surfaces and interfaces present between methylammonium lead iodide perovskite films and excess lead iodide. We show how type I and II band alignments arising under different conditions result in either passivation of surface defects or hole injection. Through first-principles simulations of solid−solid interfaces, we find that lead iodide captures holes from methylammonium lead iodide and modulates the formation of defects in the perovskite, affecting recombination. Using surfacesensitive optical spectroscopy techniques, such as transient reflectance and timeresolved photoluminescence, we show how excess lead iodide affects the diffusion and surface recombination velocity of charge carriers in methylammonium lead iodide films. Our coupled experimental and theoretical results elucidate the role of excess lead iodide in perovskite solar cells.

Continuous Modification of Perovskite Film by a Eu Complex to Fabricate the Thermal and UV-Light-Stable Solar Cells

“…The excellent performance is impressive in thin-film devices obtained by low-temperature solution processing . However, it is worth noting that this method inevitably produces several defects on the bulk and surfaces of the film. − The defects at the surface and grain boundaries of perovskite films contribute to PSCs’ performance deterioration, and they are also some of the main reasons for their poor stability. , Moreover, the inherent “soft” crystal lattice of perovskite materials makes the PSCs vulnerable to aging stresses, such as UV light, moisture, oxygen, electric field, and thermal annealing. − Currently, various strategies have been applied to enhance the resistance of PSCs to the operational environment, − which has increased the survival of PSCs from a few minutes at first to several years currently. − Many efforts have been achieved in the high-performance research of PSCs, − but their life span is still a huge barrier when translating PSCs from laboratory to commercial products …”

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

“…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. ,, …”

“…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.…”

“…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.…”

“…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. To further explore the effect of DDSI 2 modification on device performance, PSCs based on different concentrations of DDSI 2 were fabricated; the J−V curves are shown in Figure 6b, and the corresponding parameters are summarized in Table S2.…”