Direct Femtosecond Observation of Charge Carrier Recombination in Ternary Semiconductor Nanocrystals: The Effect of Composition and Shelling

Abstract

Heavy-metal free ternary semiconductor nanocrystals are emerging as key materials in photoactive applications. However, the relative abundance of intrabandgap defect states and lack of understanding of their origins within this class of nanocrystals are major factors limiting their applicability. To remove these undesirable defect states which considerably shorten the lifetimes of photogenerated excited carriers, a detailed understanding about their origin and nature is required. In this report, we monitor the ultrafast charge carrier dynamics of CuInS 2 (CIS), CuInSSe (CISSe), and CuInSe 2 (CISe) nanocrystals, before and after ZnS shelling, using state-of-the-art time-resolved laser spectroscopy with broadband capabilities. The experimental results demonstrate the presence of both electron and hole trapping intra-bandgap states in the nanocrystals which can be removed significantly by ZnS shelling, and the carrier dynamics is slowed down. Another important observation remains the reduction of carrier lifetime in the presence of Se, and the shelling strategy is observed to be less effective at suppressing trap states. This study provides quantitative physical insights into the role of anion composition and shelling on the charge carrier dynamics in ternary CIS, CISSe, and CISe nanocrystals which are essential to improve their applicability for photovoltaics and optoelectronics.

Radiative and Nonradiative Recombination in CuInS2 Nanocrystals and CuInS2-Based Core/Shell Nanocrystals

“…We assign this to excited-state absorption and will discuss its possible nature in more detail below. The observation of photoinduced absorption in CIS NCs is consistent with previous TA measurements in the red and near-infrared, 25,40 and the data presented here reveal the true magnitude of this TA spectral feature. Both the positive and negative signals decay partially on the nanosecond time scale investigated.…”

High-quality bulk hybrid perovskite single crystals within minutes by inverse temperature crystallization

“…The excitation pulse at 480 nm was generated using a spectrally tunable optical Parametric Amplifier (Light Conversion LTD) integrated to a Ti:sapphire femtosecond regenerative amplifier operating at 800 nm with 35 fs pulses and a repetition rate of 1 kHz. The white light probe pulse, on the other hand, was generated by a super continuum source2930. The pump and probe beams were overlapped spatially and temporally on the sample, and the transmitted probe light from the samples was collected and focused on the broad-band ultraviolet–visible-near-infrared detectors to record the time-resolved excitation-induced difference spectra.…”

Pure crystal orientation and anisotropic charge transport in large-area hybrid perovskite films

“…TA decays were measured with a femto-nanosecond pump-probe setup. The detailed experimental setup has been described elsewhere5455. To estimate the lifetime ( t ) at higher excitation intensities, the data were fitted with a bi-exponential decay function ( y = y 0 + A 1 e −( x − x 0)/ t 1 + A 2 e −( x − x 0)/ t 2 ), while at lower excitation intensities, the data were fitted with a single-exponential decay ( y = y 0 + A 1 e −( x − x 0)/ t 1 ).…”