To fulfill the promise of two-dimensional perovskites (2DPs) for high-performance optoelectronics, we used mechanical exfoliation to obtain n = 1 / n = 3 2DP-heterostructures and ultrafast techniques to characterize charge carriers’ dynamics at interface.
In the presence of the heterostructure, we observe the suppression of excitonic-radiative recombination and the introduction of a fast decay channel for excitons (t < 2 ns) which explains more than 80% of the total photoluminescence decay. Such evidence can be explained through ultrafast electron and hole transfer at the heterostructure interface.
Inverted perovskite solar cells passivated via organic cations exhibit superior power conversion efficiency compared to un-passivated ones. These record efficiencies have been reached thanks to the use of large organic cations to passivate the interface between the perovskite absorber and the transport layers. Here, we study the optoelectronic properties and chemical structure of interface doped perovskite solar cells where large cations, namely Cl-PEAI and F-PEAI, were incorporated at both front and rear interfaces of the absorber. The effect of the cation addition led to an increase of all the main PV characteristic, reaching PCE values up to 23.7%. We combined steady-state and time-resolved multidimensional photoluminescence imaging techniques to probe the main optoelectronic and transport properties of such devices. We thus obtained quantitative maps for physical parameters such as Quasi Fermi Level Splitting (QFLS), Urbach Energy and surface recombination rate, which proved a homogenous passivation by Cl-PEAI and F-PEAI cations over the 3D surface. For instance, the front and rear surface recombination velocities are reduced by a factor of 6 to 8 for Cl-PEAI based samples and 5 to 10 for F-PEAI based samples. In addition, we identified interfacial passivation as the main mechanism leading to a clear improvement of the Voc which increases from 1.10 to 1.16 eV. Indeed, we noticed a clear increase in terms of QFLS only after the addition of the electron transport layer whereas only an increase in the range of 0.01-0.02 eV was observed for bare perovskite thin film with the cation on top. Mapping the opto-electronical properties showed their good spatial homogeneity, By linking optical and electrical measurements we highlight the benefits of this passivation method in maximising all the main photovoltaic characteristics and in approaching inverted perovskite solar cell theoretical limit.
Charge generation at donor/acceptor interface is a highly debated topic in the organic photovoltaics (OPV)
community. The primary photoexcited state evolution happens in few femtosecond timescale, thus making very
intriguing their full understanding. In particular charge generation is believed to occur in < 200 fs, but no clear picture
emerged so far. In this work we reveal for the first time the actual charge generation mechanism following in real time
the exciton dissociation mechanism by means of sub-22 fs pump-probe spectroscopy. We study a low-band-gap polymer:
fullerene interface as an ideal system for OPV. We demonstrate that excitons dissociation leads, on a timescale of 20-50
fs, to two byproducts: bound interfacial charge transfer states (CTS) and free charges. The branching ratio of their
formation depends on the excess photon energy provided. When high energy singlet polymer states are excited, well
above the optical band gap, an ultrafast hot electron transfer happens between the polymer singlet state and the
interfacial hot CTS* due to the high electronic coupling between them. Hot exciton dissociation prevails then on internal
energy dissipation that occurs within few hundreds of fs. By measuring the internal quantum efficiency of a prototypical
device a rising trend with energy is observed, thus indicating that hot exciton dissociation effectively leads to a higher
fraction of free charges.
Conference Committee Involvement (5)
Organic, Hybrid, and Perovskite Photovoltaics XXVI
3 August 2025 | San Diego, California, United States
Organic, Hybrid, and Perovskite Photovoltaics XXV
20 August 2024 | San Diego, California, United States
Organic, Hybrid, and Perovskite Photovoltaics XXIV
22 August 2023 | San Diego, California, United States
Organic, Hybrid, and Perovskite Photovoltaics XXIII
23 August 2022 | San Diego, California, United States
Organic, Hybrid, and Perovskite Photovoltaics XXII
3 August 2021 | San Diego, California, United States
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