Chemi-Structural Stabilization of Formamidinium Lead Iodide Perovskite by Using Embedded Quantum Dots
Sofia Masi a, Carlos Echeverría-Arrondo a, Juan I. Climente b, Iván Mora-Seró a
a Universitat Jaume I, Institute of Advanced Materials (INAM) - Spain, Avinguda de Vicent Sos Baynat, Castelló de la Plana, Spain
b Universitat Jaume I, Departament de Química Física i Analítica, Spain, Avinguda de Vicent Sos Baynat, Castelló de la Plana, Spain
Proceedings of Online International Conference on Hybrid and Organic Photovoltaics (OnlineHOPV20)
Online, Spain, 2020 May 26th - 29th
Organizers: Tracey Clarke, James Durrant, Annamaria Petrozza and Trystan Watson
Poster, Sofia Masi, 123
Publication date: 22nd May 2020

In this work we demonstrate how an external additive can stabilize the formamidinium lead iodide perovskite (FAPI) without affecting its original properties. The FAPI has the lowest bandgap in the perovskite material. Its black cubic phase, desired for the photovoltaic application is not stable at ambient temperature, and a yellow hexagonal one is stable in ambient conditions.[1] However by tuning the tolerance factor using other cations, like Cs+, the band gap of the FAPI suffers of a blue-shift. So an approach that can overpass this issue is envisioned in this work. We embed the PbS QDs in the perovskite matrix, as they have the same lattice parameter of the perovskite, and upon a screening on the concentrations and size, we found that bandgap is preserved, the grains become bigger, the film more stable in air and the solar cell enhances the efficiency, the voltage and the stability. The different mechanism behind the stabilization are investigated by DFT calculations. The first mechanism is the strain, that relatively stabilize strained black phase, as its energy is lower than the energy of the bulk. Secondly, the introduction of the surface energy inverts the trend destabilizing the yellow phase. Finally the chemical bonds between the FAPI and the PbS stabilize the black phase. [2] In conclusion the stabilization is due to two distinct, but both needed, mechanisms: first, the structure stabilization that destabilizes the yellow phase due to its large surface energy and, second, the crucial chemical stabilization by chemical bonds between the PbS and FAPI that stabilizes the black phase. So the QDs could be used for the bulk epitaxial growth of the perovskite or other materials with metastable phase, which can be stabilized by the chemical bonds creation between the two different materials.

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