Research Update: Luminescence in lead halide perovskites

Efficiency and dynamics of radiative recombination of carriers are crucial figures of merit for optoelectronic materials. Following the recent success of lead halide perovskites in efficient photovoltaic and light emitting technologies, here we review some of the noted literature on the luminescence of this emerging class of materials. After outlining the theoretical formalism that is currently used to explain the carrier recombination dynamics, we review a few significant works which use photoluminescence as a tool to understand and optimize the operation of perovskite based optoelectronic devices

A dual-phase architecture for efficient amplified spontaneous emission in lead iodide perovskites

We report a way to overcome Auger recombination in lead iodide perovskites by investigating the domain structure forming below the phase transition temperature

Interfacial Morphology Addresses Performance of Perovskite Solar Cells Based on Composite Hole Transporting Materials of Functionalized Reduced Graphene Oxide and P3HT

The development of novel hole transporting materials (HTMs) for perovskite solar cells (PSCs) that can enhance device's reproducibility is a largely pursued goal, even to the detriment of a very high efficiency, since it paves the way to an effective industrialization of this technology. In this work, we study the covalent functionalization of reduced graphene oxide (RGO) flakes with different organic functional groups with the aim of increasing the stability and homogeneity of their dispersion within a poly(3-hexylthiophene) (P3HT) HTM. The selected functional groups are indeed those recalling the two characteristic moieties present in P3HT, i.e., the thienyl and alkyl residues. After preparation and characterization of a number of functionalized RGO@P3HT blends, we test the two containing the highest percentage of dispersed RGO as HTMs in PSCs and compare their performance with that of pristine P3HT and of the standard Spiro-OMeTAD HTM. Results reveal the big influence of the morphology adopted by the single RGO flakes contained in the composite HTM in driving the final device performance and allow to distinguish one of these blends as a promising material for the fabrication of highly reproducible PSCs

Enhancing Light Harvesting by Hierarchical Functionally Graded Transparent Conducting Al-doped ZnO Nano- and Mesoarchitectures

A functionally graded Al-doped ZnO structure is presented which combines conductivity, visible transparency and light scattering with mechanical flexibility. The nano and meso-architecture, constituted by a hierarchical, large surface area, mesoporous tree-like structure evolving in a compact layer, is synthesized at room temperature and is fully compatible with plastic substrates. Light trapping capability is demonstrated by showing up to 100% improvement of light absorption of a low bandgap polymer employed as the active layer.Comment: 21 pages, 6 figures, submitted to Solar Energy Materials and Solar Cell

Author Correction: Phonon coherences reveal the polaronic character of excitons in two-dimensional lead halide perovskites

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Many-Exciton Quantum Dynamics in a Ruddlesden-Popper Tin Iodide

We present a study on the many-body exciton interactions in a prototype Ruddlesden-Popper metal halide (RPMH), namely \ce{(PEA)2SnI4} (PEA = phenylethylammine), using coherent two-dimensional electronic spectroscopy. The optical dephasing times of the third-order polarization observed in these systems are determined by exciton many-body interactions and lattice fluctuations. We investigate the excitation-induced dephasing (EID) and observe a significant reduction of the contribution to the dephasing time with increasing excitation density as compared to its lead counterpart \ce{(PEA)2PbI4}, which we have previously reported [A.~R.~Srimath~Kandada~\textit{et~al.}, J.\ Chem.\ Phys.\ \textbf{153}, 164706 (2020)]. Surprisingly, we find that the EID interaction parameter is four orders of magnitude higher in \ce{(PEA)2SnI4} than that in \ce{(PEA)2PbI4}. This increase in the EID rate may be due to exciton localization arising from a more strongly statically disordered lattice in the tin derivative. This is supported by the observation of multiple closely spaced exciton states and the broadening of the linewidth with increasing population time (spectral diffusion), which suggests a static disordered structure relative to the highly dynamic lead-halide. Additionally, we find that the exciton nonlinear coherent lineshape shows evidence of a biexcitonic state with low binding energy ($<10$\,meV) not observed in the lead system. We model the lineshapes based on a stochastic scattering theory that accounts for the interaction with a non-stationary population of dark background excitations. Our study provides evidence of differences in the exciton quantum dynamics between tin- and lead-based RPMHs and links them to the exciton-exciton interaction strength and the static disorder aspect of the crystalline structure.Comment: Submitted for publicatio