Akeel M. Kadim, Amjed M. Shareef

Charge Carrier Mechanism in CdTe/ZnTe Core/Shell Nanocrystals for Photoelectrodes by Laser Ablation Method

Introduction

Charge carrier mechanism in cdte/znte core/shell nanocrystals for photoelectrodes by laser ablation method. Discover charge carrier mechanisms in CdTe/ZnTe core/shell nanocrystals for laser-ablated photoelectrodes. Enhanced mobility and reduced recombination improve device performance.

Abstract

Laser ablation in the UV-Vis absorption and emission spectra, as well as the duration increased and the emitted quantum efficiency increased., were used to synthesise and characterise of CdTe/ZnTe core/shell nanocrystals (NCs) or quantum dots (QDs). The dynamics via which carriers decrease and the distribution of excited state carriers were revealed by using ultrafast transient absorption spectroscopy to study the charge carrier process. A broad ground state bleach signal in the core/shell nanocrystals was seen in the transient absorption spectrum upon excitation by a laser pulse (Nd: YAG laser with 150 pulses and 600 mJ of power), which was consistent with the absorption spectra. These photoelectrodes were pre-sensitized by CdTe/ZnTe core/shell NCs that were deposited utilising an FTO/TPD/CdTe-ZnTe/PEDOT: PSS/Ag scaffold of a certain thickness on a transparent mesopous FTO (Fluoride tin oxide). According to PL measurements, the energygap (Eg) of CdTe/ZnTe core/shell NCs is around 2 and 2.5 eV for CdTe-core and ZnTe-shell respectively. A laser ablation-produced CdTe/ZnTe core/shell NCs improved the photoelectrodes' performance by improving the carrier's charge mobility and, therefore, recombination processes inside the NCs along with TPD and PEDOT: PSS polymer ions. A current-voltage (I-V) characteristic, in addition to lighting at 3V, verifies an ideal environment and formation. The surface trapping mechanism was eliminated because of the ZnTe shell's better surface passivation, which considerably slowed down the recombination in the core/shell nanocrystals.

Review

This manuscript investigates the charge carrier dynamics in CdTe/ZnTe core/shell nanocrystals (NCs) synthesized via laser ablation, specifically for their application in photoelectrodes. The study employs a comprehensive suite of characterization techniques, including UV-Vis absorption and emission spectroscopy, ultrafast transient absorption spectroscopy (TAS), photoluminescence (PL) measurements, and current-voltage (I-V) characteristics. The central objective is to elucidate how the core/shell structure influences charge carrier transport and recombination within a fabricated photoelectrode scaffold comprising FTO/TPD/CdTe-ZnTe/PEDOT: PSS/Ag. The key findings highlight the impact of the ZnTe shell on the charge carrier mechanism and device performance. Ultrafast transient absorption spectroscopy revealed detailed carrier dynamics and excited state distributions, showing a broad ground state bleach signal consistent with the absorption spectra of the core/shell NCs. PL measurements indicated energy gaps around 2 eV for the CdTe core and 2.5 eV for the ZnTe shell, which are critical parameters for designing efficient photoelectrodes. Importantly, the ZnTe shell was found to provide superior surface passivation, effectively eliminating surface trapping mechanisms and significantly slowing down recombination processes within the core/shell nanocrystals. This improved carrier mobility and reduced recombination were correlated with enhanced performance of the laser ablation-produced CdTe/ZnTe core/shell NC-sensitized photoelectrodes. While the study presents a compelling multi-technique approach to understand charge carrier mechanisms in core/shell nanocrystals for photoelectrode applications, some aspects of the abstract could benefit from greater clarity and precision. The description of the laser ablation synthesis and associated "duration increased and emitted quantum efficiency increased" is somewhat vague and could be refined for better understanding. Similarly, the statement regarding I-V characteristics verifying an "ideal environment and formation" lacks specific detail. Further clarification on the reported energy gaps (2 eV for CdTe-core and 2.5 eV for ZnTe-shell) would be valuable, explaining whether these refer to bulk material properties or the quantum-confined states within the core/shell system, and how they collectively determine the overall NC band gap. Detailing the precise role of TPD and PEDOT: PSS polymer ions in influencing recombination processes would also enhance the mechanistic understanding presented.

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