Radiative Recombination Processes in Halide Perovskites Observed by Light Emission Voltage Modulated Spectroscopy

Abstract

and discharge of the carriers at the contact layers; [12,[25][26][27] however, these phenomena are currently not very well understood.The light emission kinetics in perovskite LEDs and in organic light-emitting diodes (OLEDs) is usually investigated using a range of steady-state and timeresolved methods. [26,28] Remarkably, frequency-resolved methods such as impedance spectroscopy (IS) are highly effective for the separation of concomitant kinetic phenomena. [29] The connection between time transients and light-stimulated frequency methods in halide perovskite has been reviewed recently. [30] Here, we explore a new experimental measuring technique that can provide significant information about recombination in high-performance solar cells and LEDs. We analyze the frequency-resolved light emission with respect to an applied modu lated voltage, that we denote light emission voltage modulated spectroscopy (LEVS). The main point of this investigation is to reveal significant features of the radiative charge recombination that are difficult to be discerned in other measurement techniques. [30] This methodology will be especially useful when the radiative recombination event is convoluted with previous electronic carrier steps such as transport, trapping, or contact polarization effects, and/or ionic-related phenomena. It has previously been remarked that the capacitance and luminance of LEDs show correlated features [21,31,32] and some studies of electrically stimulated light emission spectroscopy have been reported, [33][34][35] but unfortunately, a general methodology has not been fully developed.Here we describe the first LEVS experiments in halide perovskite LEDs and establish an equivalent circuit model to understand the observed spectra, based on the previous experience in IS. We show that the method provides unique information on the recombination processes that cannot be accessed by purely electrical techniques, thus highlighting the interest of this new experimental technique for the characterization of optoelectronic devices, especially those presenting multiple physical phenomena, as it is the case of halide perovskite-based systems. The Transfer Functions of Frequency Resolved Measurements IS is a general-purpose characterization technique that is used in a large variety of fields to extract dynamic information on anyThe kinetics of light emission in halide perovskite light-emitting diodes (LEDs) and solar cells is composed of a radiative recombination of voltage-injected carriers mediated by additional steps such as carrier trapping, redistribution of injected carriers, and photon recycling that affect the observed luminescence decays. These processes are investigated in high-performance halide perovskite LEDs, with external quantum efficiency (EQE) and luminance values higher than 20% and 80 000 Cd m −2 , by measuring the frequency-resolved emitted light with respect to modulated voltage through a new methodology termed light emission voltage modulated spectroscopy (LEVS). The spectra are shown to provid...

Fully Inkjet‐Printed Green‐Emitting PEDOT:PSS/NiO/Colloidal CsPbBr3/SnO2 Perovskite Light‐Emitting Diode on Rigid and Flexible Substrates

“…Finally, the solid was weighed (60–70 mg was typically obtained), redispersed in the corresponding volume of hexane or dodecane (typically 6–7 mL) to obtain a concentration of 10 mg mL −1 , and filtered through a 0.42 μm Teflon filter for device's fabrication. [ 54 ]…”

“…Finally, the solid was weighed (60-70 mg was typically obtained), redispersed in the corresponding volume of hexane or dodecane (typically 6-7 mL) to obtain a concentration of 10 mg mL À1 , and filtered through a 0.42 μm Teflon filter for device's fabrication. [54] Preparation of Inkjet-Printable Inks Based on CsPbBr 3 Nanocrystals: Two colloidal solution of CsPbBr 3 NCs in dodecane and CsPbBr 3 NCs in hexane (both prepared selecting the proper aforementioned methods) were mixed (ratio of dodecane/hexane 3:1), preserving the NC final concentration in the solution to be around 10% in weight. [35] The obtained colloidal solution was stirred at room temperature and the supernatant was collected.…”

Dispersive Charge Transfer State Electroluminescence in Organic Solar Cells

“…The signal output from the impedance analyzer is therefore the ratio of the complex EL intensity (magnitude and phase) to the complex current density or, in other words, a frequency-dependent complex quantum efficiency. This technique has previously been used to study defect and tail states in inorganic LEDs, [27][28][29] but has yet to be applied to organic solar cells.…”

“…Indeed, this assumption underlies the photovoltaic reciprocity relations that are widely used to analyze OPVs. [18,20,21] Here, we apply modulation electroluminescence spectroscopy (MELS) [27][28][29] to demonstrate that CT EL from both bulk and planar heterojunction small molecule OPV cells is dispersive. That is, CT emission on the high energy side of the electroluminescence (EL) spectrum exhibits a different modulation response (i.e., magnitude and phase as a function of modulation frequency, in direct analogy to impedance spectroscopy) than CT emission on the low-energy side of the EL spectrum.…”

Ion‐Mediated Recombination Dynamics in Perovskite‐Based Memory Light‐Emitting Diodes for Neuromorphic Control Systems

“…Furthermore, the low formation energies of the defects make them easily redistributed in the bulk film or across interfaces under the application of an electric field. [ 13 ] Both the ease of ionic transport and the high PLQY highlight its potential for constructing LED with embedded memory attributed to the slow ionic drift‐diffusion dynamics. Within the family of perovskites, Ruddlesden–Popper (RP) perovskites (L 2 A m−1 B m X 3m+1 ; where L, A, B, X, and m refer to the bulky spacer cation, A‐site cation, metal ion, halide anion, and the degree of L‐cation integration into the perovskite lattice, respectively) are favored for constructing efficient LED due to its intrinsic multi‐quantum well structure that support high radiative recombination.…”