Theoretical Study on the Stability of Formamidinium Lead Iodide Perovskite by Using Embedded Quantum Dots.
David Macias a b, Carlos Echeverría b, Juan I. Climente b, Josep Planelles b, Sofia Masi a, 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 University Jaume I, Spain, Avinguda de Vicent Sos Baynat, Castelló de la Plana, Spain
Poster, David Macias, 094
Publication date: 25th November 2019

Halide perovskites solar cells have emerged as a promising material for applications in optoelectronic devices due to their good transport properties and composition versatiblity.  Formamidinium lead iodide (FAPI) perovskite phase has given rise to a special interest as it has the lowest band gap among halide perovskites with a maximal theoretical PCEmax of 32.3%. [1] However, it spontaneously degrades into a hexagonal (photoinactive) phase and its stability is an issue.[2] The approaches to stabilize the perovskite structure of (FAPI) commonly result in a blue shift of the band gap, which limits the maximum photoconversion efficiency. Recent experimental evidence shows that embedding colloidal PbS quantum dots (QDs) in a FAPI matrix stabilizes the perovskite phase and reduces the annealing temperature, while preserving its small band gap.[3]

In this work we study theoretically the main factors of the QDs inclusion in the host FAPI matrix by carrying out DFT calculations including spin-orbit coupling, theoretical k · p analysis and linear elastic theory of continuous media. We show that stabilization results from: (i) the smaller lattice constant of PbS generates strain that destabilizes the perovskite phase, but the effect is more pronounced in the hexagonal phase, (ii) crystal surfaces arise on the interface with the QD destabilizing the hexagonal phase relative to the perovskite one and (iii) chemical bonds form between the two materials further stabilize the perovskite phase.[3]

We also investigate how the FAPI matrix influences the optical spectrum of PbS dots. k·p simulations provide complete information on exciton binding energies, dielectric mismatch effects, band alignment between FAPI and PbS QDs, as well as size-dependent absorption in PbS/FAPI QDs.

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