Lead-halide perovskites are materials that show promising trends for semiconductor research and light-harvesting applications. Despite impressive breakthroughs in attaining higher photoconversion efficiencies, the long-term stability of perovskite solar cells remains a challenge. The introduction of a 2D perovskite layer over a bulk 3D perovskite film is thought to create an interface that significantly improves the stability of the solar cell. While the observation of enhanced stability is an important development, an understanding of the effects of operational light and heat conditions on the stability of the 2D/3D interface is also necessary. The light and heat induced changes in the 2D (PEA₂PbI₄) layer deposited on a 3D film of MAPbI₃ are probed through changes in absorption, emission, and XRD spectra. Distinct 2D and 3D absorption and emission from the interface are observed, with a continuous decrease in the 2D emission and absorption under visible light irradiation. This is attributed to unstable behavior of the 2D layer as the PEA⁺ cations diffuse into the bulk 3D phase. Thermal variations also induced a continuous decrease in 2D emission, with increasing rates as the temperature was increased. The rates of this emission disappearance at temperatures between 30 and 120 °C followed pseudo-first order kinetics. The charge carrier lifetime of the 2D/3D films was also probed and demonstrated an increase indicative of cation dissipation within the 3D phase of the perovskite film. This transformation was supported by XRD measurements that confirmed the presence of both 2D and 3D phases before heating, but only 3D XRD peaks after heating. By confirming the instability of the 2D/3D interface under operational conditions, this research suggests a need for further work to understand additional pathways to improved stability of the perovskite solar cell while maintaining the 2D/3D interface.

Nathaniel Hiott

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