Radiative Recombination and Photon Recycling in Bulk and Quasi-2D Metal Halide Perovskites
Laura Herz a
a University of Oxford, Department of Physics, Clarendon Laboratory, UK, Parks Road, United Kingdom
nanoGe Perovskite Conferences
Proceedings of International Conference on Perovskite Thin Film Photovoltaics and Perovskite Photonics and Optoelectronics (NIPHO20)
Sevilla, Spain, 2020 February 23rd - 25th
Organizer: Hernán Míguez
Invited Speaker, Laura Herz, presentation 008
DOI: https://doi.org/10.29363/nanoge.nipho.2020.008
Publication date: 25th November 2019

Organic-inorganic metal halide perovskites have emerged as attractive materials for solar cells with power-conversion efficiencies now exceeding 23%. As these devices are approaching the Shockley-Queisser limit, bimolecular (band-to-band) recombination will dominate the charge-carrier losses, with trap-mediated charge recombination becoming less prominent.

We show that in methylammonium lead triiodide perovskite, bimolecular recombination can be fully explained as the inverse of absorption,[1] and exhibits a dynamic that is heavily influenced by photon reabsorption inside the material.[2,3] Such photon recycling is shown to slow charge losses from thin hybrid perovskite films, depending on light out-coupling.[2] Interestingly, for thin films comprising a quasi-two-dimensional (2D) perovskite region interfaced with a 3D MAPbI3 perovskite layer the blue-shifted emission originating from quasi-2D regions overlaps significantly with the absorption spectrum of the 3D perovskite, allowing for highly effective “heterogeneous photon recycling”. We show that this combination fully compensates for the adverse effects of electronic confinement, yielding quasi-2D perovskites with highly efficient charge transporting properties.[3]

In addition, we investigate optoelectronic properties of mixed tin-lead iodide and mixed iodide-bromide lead perovskites. We show how band-gap bowing in tin-lead perovskites is compatible with a mechanism arising from bond bending to accommodate the random placement of unevenly sized lead and tin ions.[4] While tin-rich compositions exhibit fast, mono-exponential recombination that is almost temperature-independent, in accordance with high levels of electrical doping,[4,5] lead-rich compositions show slower, stretched-exponential charge-carrier recombination that is strongly temperature-dependent, in accordance with a multiphonon assisted process. Finally, in the context of silicon-perovskite tandem cells, we discuss the mechanisms underlying detrimental halide segregation in mixed iodide-bromide lead perovskites with desirable electronic band gaps near 1.75eV.[6]

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