Humidity‐Induced Degradation via Grain Boundaries of HC(NH₂)₂PbI₃ Planar Perovskite Solar Cells

Abstract

The sensitivity of organic–inorganic perovskites to environmental factors remains a major barrier for these materials to become commercially viable for photovoltaic applications. In this work, the degradation of formamidinium lead iodide (FAPbI3) perovskite in a moist environment is systematically investigated. It is shown that the level of relative humidity (RH) is important for the onset of degradation processes. Below 30% RH, the black phase of the FAPbI3 perovskite shows excellent phase stability over 90 d. Once the RH reaches 50%, degradation of the FAPbI3 perovskite occurs rapidly. Results from a Kelvin probe force microscopy study reveal that the formation of nonperovskite phases initiates at the grain boundaries and the phase transition proceeds toward the grain interiors. Also, ion migration along the grain boundaries is greatly enhanced upon degradation. A post‐thermal treatment (PTT) that removes chemical residues at the grain boundaries which effectively slows the degradation process is developed. Finally, it is demonstrated that the PTT process improves the performance and stability of the final device.

The Impact of a Dynamic Two‐Step Solution Process on Film Formation of Cs0.15(MA0.7FA0.3)0.85PbI3 Perovskite and Solar Cell Performance

“…To verify the film formation dynamics deduced from the FTIR results, XRD scans of as‐deposited PbI 2 ‐CsI film (green), static processed PbI 2 ‐CsI‐MAI‐FAI film (blue) and dynamic processed PbI 2 ‐CsI‐MAI‐FAI film (red) were also obtained and shown in Figure a. In the static processed PbI 2 ‐CsI‐MAI‐FAI film, there are significantly stronger peaks at 11.0○ and 11.7○, representing the strong presence of nonperovskite phases which could be leftover FAI‐MAI mixed with PbI 2 ‐DMF, hydrated compound, or perovskite delta phase . These peaks are less prominent in the dynamic‐processed film.…”

Μethylammonium Chloride: A Key Additive for Highly Efficient, Stable, and Up‐Scalable Perovskite Solar Cells

“…2019, 2, 79-92 the reaction between the Ag electrode and the perovskite film due to the diffusion of silver. [101][102][103] [66] A more precise comparison of the stability of solar cells with or without MACl has been realized by Lee and coworkers who added an amount of MACl (20-40%) which is close to that typically used to fabricate solar cells of a PCE over 22%.…”

Unveiling the Importance of Precursor Preparation for Highly Efficient and Stable Phenethylammonium‐Based Perovskite Solar Cells

“…To observe morphological and electronic property differences between DP perovskite and SP perovskite, scanning electron microscopy (SEM) and Kelvin probe force microscopy (KPFM) were performed in dark on test structures (perovskite/mp‐TiO 2 /bl‐TiO 2 /FTO glass). KPFM provides spatial work function distribution of the surface of a sample which has been shown to be a powerful method for providing local electrical properties of the film surface in relation to its morphology . For comparison, 3D perovskite is also measured as a control sample.…”

“…For comparison, 3D perovskite is also measured as a control sample. During the KPFM measurement, the perovskite surface is directly accessible by the KPFM probe, whereas the FTO layer is grounded . Results of SEM and KPFM measurements are shown in Figure and Figure S9, Supporting Information.…”